Security hardening

Red Hat Enterprise Linux 8

Securing Red Hat Enterprise Linux 8

Red Hat Customer Content Services

Abstract

This title assists users and administrators in learning the processes and practices of securing workstations and servers against local and remote intrusion, exploitation, and malicious activity. Focused on Red Hat Enterprise Linux but detailing concepts and techniques valid for all Linux systems, this guide details the planning and the tools involved in creating a secured computing environment for the data center, workplace, and home. With proper administrative knowledge, vigilance, and tools, systems running Linux can be both fully functional and secured from most common intrusion and exploit methods.

Making open source more inclusive

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Chapter 1. Overview of security hardening in RHEL

Due to the increased reliance on powerful, networked computers to help run businesses and keep track of our personal information, entire industries have been formed around the practice of network and computer security. Enterprises have solicited the knowledge and skills of security experts to properly audit systems and tailor solutions to fit the operating requirements of their organization. Because most organizations are increasingly dynamic in nature, their workers are accessing critical company IT resources locally and remotely, hence the need for secure computing environments has become more pronounced.

Unfortunately, many organizations, as well as individual users, regard security as more of an afterthought, a process that is overlooked in favor of increased power, productivity, convenience, ease of use, and budgetary concerns. Proper security implementation is often enacted postmortem — after an unauthorized intrusion has already occurred. Taking the correct measures prior to connecting a site to an untrusted network, such as the Internet, is an effective means of thwarting many attempts at intrusion.

1.1. What is computer security?

Computer security is a general term that covers a wide area of computing and information processing. Industries that depend on computer systems and networks to conduct daily business transactions and access critical information regard their data as an important part of their overall assets. Several terms and metrics have entered our daily business vocabulary, such as total cost of ownership (TCO), return on investment (ROI), and quality of service (QoS). Using these metrics, industries can calculate aspects such as data integrity and high-availability (HA) as part of their planning and process management costs. In some industries, such as electronic commerce, the availability and trustworthiness of data can mean the difference between success and failure.

1.2. Standardizing security

Enterprises in every industry rely on regulations and rules that are set by standards-making bodies such as the American Medical Association (AMA) or the Institute of Electrical and Electronics Engineers (IEEE). The same concepts hold true for information security. Many security consultants and vendors agree upon the standard security model known as CIA, or Confidentiality, Integrity, and Availability. This three-tiered model is a generally accepted component to assessing risks of sensitive information and establishing security policy. The following describes the CIA model in further detail:

Confidentiality — Sensitive information must be available only to a set of pre-defined individuals. Unauthorized transmission and usage of information should be restricted. For example, confidentiality of information ensures that a customer’s personal or financial information is not obtained by an unauthorized individual for malicious purposes such as identity theft or credit fraud.
Integrity — Information should not be altered in ways that render it incomplete or incorrect. Unauthorized users should be restricted from the ability to modify or destroy sensitive information.
Availability — Information should be accessible to authorized users any time that it is needed. Availability is a warranty that information can be obtained with an agreed-upon frequency and timeliness. This is often measured in terms of percentages and agreed to formally in Service Level Agreements (SLAs) used by network service providers and their enterprise clients.

1.3. Cryptographic software and certifications

Red Hat Enterprise Linux undergoes several security certifications, such as FIPS 140-2 or Common Criteria (CC), to ensure that industry best practices are followed.

The RHEL 8 core crypto components Knowledgebase article provides an overview of the Red Hat Enterprise Linux 8 core crypto components, documenting which are they, how are they selected, how are they integrated into the operating system, how do they support hardware security modules and smart cards, and how do crypto certifications apply to them.

1.4. Security controls

Computer security is often divided into three distinct main categories, commonly referred to as controls:

Physical
Technical
Administrative

These three broad categories define the main objectives of proper security implementation. Within these controls are sub-categories that further detail the controls and how to implement them.

1.4.1. Physical controls

Physical control is the implementation of security measures in a defined structure used to deter or prevent unauthorized access to sensitive material. Examples of physical controls are:

Closed-circuit surveillance cameras
Motion or thermal alarm systems
Security guards
Picture IDs
Locked and dead-bolted steel doors
Biometrics (includes fingerprint, voice, face, iris, handwriting, and other automated methods used to recognize individuals)

1.4.2. Technical controls

Technical controls use technology as a basis for controlling the access and usage of sensitive data throughout a physical structure and over a network. Technical controls are far-reaching in scope and encompass such technologies as:

Encryption
Smart cards
Network authentication
Access control lists (ACLs)
File integrity auditing software

1.4.3. Administrative controls

Administrative controls define the human factors of security. They involve all levels of personnel within an organization and determine which users have access to what resources and information by such means as:

Training and awareness
Disaster preparedness and recovery plans
Personnel recruitment and separation strategies
Personnel registration and accounting

1.5. Vulnerability assessment

Given time, resources, and motivation, an attacker can break into nearly any system. All of the security procedures and technologies currently available cannot guarantee that any systems are completely safe from intrusion. Routers help secure gateways to the Internet. Firewalls help secure the edge of the network. Virtual Private Networks safely pass data in an encrypted stream. Intrusion detection systems warn you of malicious activity. However, the success of each of these technologies is dependent upon a number of variables, including:

The expertise of the staff responsible for configuring, monitoring, and maintaining the technologies.
The ability to patch and update services and kernels quickly and efficiently.
The ability of those responsible to keep constant vigilance over the network.

Given the dynamic state of data systems and technologies, securing corporate resources can be quite complex. Due to this complexity, it is often difficult to find expert resources for all of your systems. While it is possible to have personnel knowledgeable in many areas of information security at a high level, it is difficult to retain staff who are experts in more than a few subject areas. This is mainly because each subject area of information security requires constant attention and focus. Information security does not stand still.

A vulnerability assessment is an internal audit of your network and system security; the results of which indicate the confidentiality, integrity, and availability of your network. Typically, vulnerability assessment starts with a reconnaissance phase, during which important data regarding the target systems and resources is gathered. This phase leads to the system readiness phase, whereby the target is essentially checked for all known vulnerabilities. The readiness phase culminates in the reporting phase, where the findings are classified into categories of high, medium, and low risk; and methods for improving the security (or mitigating the risk of vulnerability) of the target are discussed

If you were to perform a vulnerability assessment of your home, you would likely check each door to your home to see if they are closed and locked. You would also check every window, making sure that they closed completely and latch correctly. This same concept applies to systems, networks, and electronic data. Malicious users are the thieves and vandals of your data. Focus on their tools, mentality, and motivations, and you can then react swiftly to their actions.

1.5.1. Defining assessment and testing

Vulnerability assessments may be broken down into one of two types: outside looking in and inside looking around.

When performing an outside-looking-in vulnerability assessment, you are attempting to compromise your systems from the outside. Being external to your company provides you with the cracker’s point of view. You see what a cracker sees — publicly-routable IP addresses, systems on your DMZ, external interfaces of your firewall, and more. DMZ stands for "demilitarized zone", which corresponds to a computer or small subnetwork that sits between a trusted internal network, such as a corporate private LAN, and an untrusted external network, such as the public Internet. Typically, the DMZ contains devices accessible to Internet traffic, such as web (HTTP) servers, FTP servers, SMTP (e-mail) servers and DNS servers.

When you perform an inside-looking-around vulnerability assessment, you are at an advantage since you are internal and your status is elevated to trusted. This is the point of view you and your co-workers have once logged on to your systems. You see print servers, file servers, databases, and other resources.

There are striking distinctions between the two types of vulnerability assessments. Being internal to your company gives you more privileges than an outsider. In most organizations, security is configured to keep intruders out. Very little is done to secure the internals of the organization (such as departmental firewalls, user-level access controls, and authentication procedures for internal resources). Typically, there are many more resources when looking around inside as most systems are internal to a company. Once you are outside the company, your status is untrusted. The systems and resources available to you externally are usually very limited.

Consider the difference between vulnerability assessments and penetration tests. Think of a vulnerability assessment as the first step to a penetration test. The information gleaned from the assessment is used for testing. Whereas the assessment is undertaken to check for holes and potential vulnerabilities, the penetration testing actually attempts to exploit the findings.

Assessing network infrastructure is a dynamic process. Security, both information and physical, is dynamic. Performing an assessment shows an overview, which can turn up false positives and false negatives. A false positive is a result, where the tool finds vulnerabilities which in reality do not exist. A false negative is when it omits actual vulnerabilities.

Security administrators are only as good as the tools they use and the knowledge they retain. Take any of the assessment tools currently available, run them against your system, and it is almost a guarantee that there are some false positives. Whether by program fault or user error, the result is the same. The tool may find false positives, or, even worse, false negatives.

Now that the difference between a vulnerability assessment and a penetration test is defined, take the findings of the assessment and review them carefully before conducting a penetration test as part of your new best practices approach.

Warning

Do not attempt to exploit vulnerabilities on production systems. Doing so can have adverse effects on productivity and efficiency of your systems and network.

The following list examines some of the benefits of performing vulnerability assessments.

Creates proactive focus on information security.
Finds potential exploits before crackers find them.
Results in systems being kept up to date and patched.
Promotes growth and aids in developing staff expertise.
Abates financial loss and negative publicity.

1.5.2. Establishing a methodology for vulnerability assessment

To aid in the selection of tools for a vulnerability assessment, it is helpful to establish a vulnerability assessment methodology. Unfortunately, there is no predefined or industry approved methodology at this time; however, common sense and best practices can act as a sufficient guide.

What is the target? Are we looking at one server, or are we looking at our entire network and everything within the network? Are we external or internal to the company? The answers to these questions are important as they help determine not only which tools to select but also the manner in which they are used.

To learn more about establishing methodologies, see the following website:

https://www.owasp.org/ — The Open Web Application Security Project

1.5.3. Vulnerability assessment tools

An assessment can start by using some form of an information-gathering tool. When assessing the entire network, map the layout first to find the hosts that are running. Once located, examine each host individually. Focusing on these hosts requires another set of tools. Knowing which tools to use may be the most crucial step in finding vulnerabilities.

The following tools are just a small sampling of the available tools:

Nmap is a popular tool that can be used to find host systems and open ports on those systems. To install Nmap from the AppStream repository, enter the yum install nmap command as the root user. See the nmap(1) man page for more information.
The tools from the OpenSCAP suite, such as the oscap command-line utility and the scap-workbench graphical utility, provides a fully automated compliance audit. See Scanning the system for security compliance and vulnerabilities for more information.
Advanced Intrusion Detection Environment (AIDE) is a utility that creates a database of files on the system, and then uses that database to ensure file integrity and detect system intrusions. See Checking integrity with AIDE for more information.

1.6. Security threats

1.6.1. Threats to network security

Bad practices when configuring the following aspects of a network can increase the risk of an attack.

Insecure architectures

A misconfigured network is a primary entry point for unauthorized users. Leaving a trust-based, open local network vulnerable to the highly-insecure Internet is much like leaving a door ajar in a crime-ridden neighborhood — nothing may happen for an arbitrary amount of time, but someone exploits the opportunity eventually.

Broadcast networks

System administrators often fail to realize the importance of networking hardware in their security schemes. Simple hardware, such as hubs and routers, relies on the broadcast or non-switched principle; that is, whenever a node transmits data across the network to a recipient node, the hub or router sends a broadcast of the data packets until the recipient node receives and processes the data. This method is the most vulnerable to address resolution protocol (ARP) or media access control (MAC) address spoofing by both outside intruders and unauthorized users on local hosts.

Centralized servers

Another potential networking pitfall is the use of centralized computing. A common cost-cutting measure for many businesses is to consolidate all services to a single powerful machine. This can be convenient as it is easier to manage and costs considerably less than multiple-server configurations. However, a centralized server introduces a single point of failure on the network. If the central server is compromised, it may render the network completely useless or worse, prone to data manipulation or theft. In these situations, a central server becomes an open door that allows access to the entire network.

1.6.2. Threats to server security

Server security is as important as network security because servers often hold a great deal of an organization’s vital information. If a server is compromised, all of its contents may become available for the cracker to steal or manipulate at will. The following sections detail some of the main issues.

Unused services and open ports

A full installation of Red Hat Enterprise Linux 8 contains more than 1000 applications and library packages. However, most server administrators do not opt to install every single package in the distribution, preferring instead to install a base installation of packages, including several server applications.

A common occurrence among system administrators is to install the operating system without paying attention to what programs are actually being installed. This can be problematic because unneeded services may be installed, configured with the default settings, and possibly turned on. This can cause unwanted services, such as Telnet, DHCP, or DNS, to run on a server or workstation without the administrator realizing it, which in turn can cause unwanted traffic to the server or even a potential pathway into the system for crackers.

Unpatched services

Most server applications that are included in a default installation are solid, thoroughly tested pieces of software. Having been in use in production environments for many years, their code has been thoroughly refined and many of the bugs have been found and fixed.

However, there is no such thing as perfect software and there is always room for further refinement. Moreover, newer software is often not as rigorously tested as one might expect, because of its recent arrival to production environments or because it may not be as popular as other server software.

Developers and system administrators often find exploitable bugs in server applications and publish the information on bug tracking and security-related websites such as the Bugtraq mailing list (http://www.securityfocus.com) or the Computer Emergency Response Team (CERT) website (http://www.cert.org). Although these mechanisms are an effective way of alerting the community to security vulnerabilities, it is up to system administrators to patch their systems promptly. This is particularly true because crackers have access to these same vulnerability tracking services and will use the information to crack unpatched systems whenever they can. Good system administration requires vigilance, constant bug tracking, and proper system maintenance to ensure a more secure computing environment.

Inattentive administration

Administrators who fail to patch their systems are one of the greatest threats to server security. This applies as much to inexperienced administrators as it does to overconfident or amotivated administrators.

Some administrators fail to patch their servers and workstations, while others fail to watch log messages from the system kernel or network traffic. Another common error is when default passwords or keys to services are left unchanged. For example, some databases have default administration passwords because the database developers assume that the system administrator changes these passwords immediately after installation. If a database administrator fails to change this password, even an inexperienced cracker can use a widely-known default password to gain administrative privileges to the database. These are only a few examples of how inattentive administration can lead to compromised servers.

Inherently insecure services

Even the most vigilant organization can fall victim to vulnerabilities if the network services they choose are inherently insecure. For instance, there are many services developed under the assumption that they are used over trusted networks; however, this assumption fails as soon as the service becomes available over the Internet — which is itself inherently untrusted.

One category of insecure network services are those that require unencrypted user names and passwords for authentication. Telnet and FTP are two such services. If packet sniffing software is monitoring traffic between the remote user and such a service user names and passwords can be easily intercepted.

Inherently, such services can also more easily fall prey to what the security industry terms the man-in-the-middle attack. In this type of attack, a cracker redirects network traffic by tricking a cracked name server on the network to point to his machine instead of the intended server. Once someone opens a remote session to the server, the attacker’s machine acts as an invisible conduit, sitting quietly between the remote service and the unsuspecting user capturing information. In this way a cracker can gather administrative passwords and raw data without the server or the user realizing it.

Another category of insecure services include network file systems and information services such as NFS or NIS, which are developed explicitly for LAN usage but are, unfortunately, extended to include WANs (for remote users). NFS does not, by default, have any authentication or security mechanisms configured to prevent a cracker from mounting the NFS share and accessing anything contained therein. NIS, as well, has vital information that must be known by every computer on a network, including passwords and file permissions, within a plain text ASCII or DBM (ASCII-derived) database. A cracker who gains access to this database can then access every user account on a network, including the administrator’s account.

By default, Red Hat Enterprise Linux 8 is released with all such services turned off. However, since administrators often find themselves forced to use these services, careful configuration is critical.

1.6.3. Threats to workstation and home PC security

Workstations and home PCs may not be as prone to attack as networks or servers, but because they often contain sensitive data, such as credit card information, they are targeted by system crackers. Workstations can also be co-opted without the user’s knowledge and used by attackers as "bot" machines in coordinated attacks. For these reasons, knowing the vulnerabilities of a workstation can save users the headache of reinstalling the operating system, or worse, recovering from data theft.

Bad passwords

Bad passwords are one of the easiest ways for an attacker to gain access to a system.

Vulnerable client applications

Although an administrator may have a fully secure and patched server, that does not mean remote users are secure when accessing it. For instance, if the server offers Telnet or FTP services over a public network, an attacker can capture the plain text user names and passwords as they pass over the network, and then use the account information to access the remote user’s workstation.

Even when using secure protocols, such as SSH, a remote user may be vulnerable to certain attacks if they do not keep their client applications updated. For instance, SSH protocol version 1 clients are vulnerable to an X-forwarding attack from malicious SSH servers. Once connected to the server, the attacker can quietly capture any keystrokes and mouse clicks made by the client over the network. This problem was fixed in the SSH version 2 protocol, but it is up to the user to keep track of what applications have such vulnerabilities and update them as necessary.

1.7. Common exploits and attacks

Table 1.1, “Common exploits” details some of the most common exploits and entry points used by intruders to access organizational network resources. Key to these common exploits are the explanations of how they are performed and how administrators can properly safeguard their network against such attacks.

Table 1.1. Common exploits

Exploit	Description	Notes
Null or default passwords	Leaving administrative passwords blank or using a default password set by the product vendor. This is most common in hardware such as routers and firewalls, but some services that run on Linux can contain default administrator passwords as well (though Red Hat Enterprise Linux 8 does not ship with them).	Commonly associated with networking hardware such as routers, firewalls, VPNs, and network attached storage (NAS) appliances. Common in many legacy operating systems, especially those that bundle services (such as UNIX and Windows.) Administrators sometimes create privileged user accounts in a rush and leave the password null, creating a perfect entry point for malicious users who discover the account.
Default shared keys	Secure services sometimes package default security keys for development or evaluation testing purposes. If these keys are left unchanged and are placed in a production environment on the Internet, all users with the same default keys have access to that shared-key resource, and any sensitive information that it contains.	Most common in wireless access points and preconfigured secure server appliances.
IP spoofing	A remote machine acts as a node on your local network, finds vulnerabilities with your servers, and installs a backdoor program or Trojan horse to gain control over your network resources.	Spoofing is quite difficult as it involves the attacker predicting TCP/IP sequence numbers to coordinate a connection to target systems, but several tools are available to assist crackers in performing such a vulnerability. Depends on target system running services (such as `rsh`, `telnet`, FTP and others) that use source-based authentication techniques, which are not recommended when compared to PKI or other forms of encrypted authentication used in `ssh` or SSL/TLS.
Eavesdropping	Collecting data that passes between two active nodes on a network by eavesdropping on the connection between the two nodes.	This type of attack works mostly with plain text transmission protocols such as Telnet, FTP, and HTTP transfers. Remote attacker must have access to a compromised system on a LAN in order to perform such an attack; usually the cracker has used an active attack (such as IP spoofing or man-in-the-middle) to compromise a system on the LAN. Preventative measures include services with cryptographic key exchange, one-time passwords, or encrypted authentication to prevent password snooping; strong encryption during transmission is also advised.
Service vulnerabilities	An attacker finds a flaw or loophole in a service run over the Internet; through this vulnerability, the attacker compromises the entire system and any data that it may hold, and could possibly compromise other systems on the network.	HTTP-based services such as CGI are vulnerable to remote command execution and even interactive shell access. Even if the HTTP service runs as a non-privileged user such as "nobody", information such as configuration files and network maps can be read, or the attacker can start a denial of service attack which drains system resources or renders it unavailable to other users. Services sometimes can have vulnerabilities that go unnoticed during development and testing; these vulnerabilities (such as buffer overflows, where attackers crash a service using arbitrary values that fill the memory buffer of an application, giving the attacker an interactive command prompt from which they may execute arbitrary commands) can give complete administrative control to an attacker. Administrators should make sure that services do not run as the root user, and should stay vigilant of patches and errata updates for applications from vendors or security organizations such as CERT and CVE.
Application vulnerabilities	Attackers find faults in desktop and workstation applications (such as email clients) and execute arbitrary code, implant Trojan horses for future compromise, or crash systems. Further exploitation can occur if the compromised workstation has administrative privileges on the rest of the network.	Workstations and desktops are more prone to exploitation as workers do not have the expertise or experience to prevent or detect a compromise; it is imperative to inform individuals of the risks they are taking when they install unauthorized software or open unsolicited email attachments. Safeguards can be implemented such that email client software does not automatically open or execute attachments. Additionally, the automatic update of workstation software using Red Hat Network; or other system management services can alleviate the burdens of multi-seat security deployments.
Denial of Service (DoS) attacks	Attacker or group of attackers coordinate against an organization’s network or server resources by sending unauthorized packets to the target host (either server, router, or workstation). This forces the resource to become unavailable to legitimate users.	The most reported DoS case in the US occurred in 2000. Several highly-trafficked commercial and government sites were rendered unavailable by a coordinated ping flood attack using several compromised systems with high bandwidth connections acting as zombies, or redirected broadcast nodes. Source packets are usually forged (as well as rebroadcast), making investigation as to the true source of the attack difficult. Advances in ingress filtering (IETF rfc2267) using `iptables` and Network Intrusion Detection Systems such as `snort` assist administrators in tracking down and preventing distributed DoS attacks.

Chapter 2. Securing RHEL during installation

Security begins even before you start the installation of Red Hat Enterprise Linux. Configuring your system securely from the beginning makes it easier to implement additional security settings later.

2.1. BIOS and UEFI security

Password protection for the BIOS (or BIOS equivalent) and the boot loader can prevent unauthorized users who have physical access to systems from booting using removable media or obtaining root privileges through single user mode. The security measures you should take to protect against such attacks depends both on the sensitivity of the information on the workstation and the location of the machine.

For example, if a machine is used in a trade show and contains no sensitive information, then it may not be critical to prevent such attacks. However, if an employee’s laptop with private, unencrypted SSH keys for the corporate network is left unattended at that same trade show, it could lead to a major security breach with ramifications for the entire company.

If the workstation is located in a place where only authorized or trusted people have access, however, then securing the BIOS or the boot loader may not be necessary.

2.1.1. BIOS passwords

The two primary reasons for password protecting the BIOS of a computer are^[1]:

Preventing changes to BIOS settings — If an intruder has access to the BIOS, they can set it to boot from a CD-ROM or a flash drive. This makes it possible for them to enter rescue mode or single user mode, which in turn allows them to start arbitrary processes on the system or copy sensitive data.
Preventing system booting — Some BIOSes allow password protection of the boot process. When activated, an attacker is forced to enter a password before the BIOS launches the boot loader.

Because the methods for setting a BIOS password vary between computer manufacturers, consult the computer’s manual for specific instructions.

If you forget the BIOS password, it can either be reset with jumpers on the motherboard or by disconnecting the CMOS battery. For this reason, it is good practice to lock the computer case if possible. However, consult the manual for the computer or motherboard before attempting to disconnect the CMOS battery.

2.1.2. Non-BIOS-based systems security

Other systems and architectures use different programs to perform low-level tasks roughly equivalent to those of the BIOS on x86 systems. For example, the Unified Extensible Firmware Interface (UEFI) shell.

For instructions on password protecting BIOS-like programs, see the manufacturer’s instructions.

2.2. Disk partitioning

Red Hat recommends creating separate partitions for the /boot, /, /home, /tmp, and /var/tmp/ directories.

/boot: This partition is the first partition that is read by the system during boot up. The boot loader and kernel images that are used to boot your system into Red Hat Enterprise Linux 8 are stored in this partition. This partition should not be encrypted. If this partition is included in / and that partition is encrypted or otherwise becomes unavailable then your system is not able to boot.
/home: When user data (/home) is stored in / instead of in a separate partition, the partition can fill up causing the operating system to become unstable. Also, when upgrading your system to the next version of Red Hat Enterprise Linux 8 it is a lot easier when you can keep your data in the /home partition as it is not be overwritten during installation. If the root partition (/) becomes corrupt your data could be lost forever. By using a separate partition there is slightly more protection against data loss. You can also target this partition for frequent backups.
/tmp and /var/tmp/: Both the /tmp and /var/tmp/ directories are used to store data that does not need to be stored for a long period of time. However, if a lot of data floods one of these directories it can consume all of your storage space. If this happens and these directories are stored within / then your system could become unstable and crash. For this reason, moving these directories into their own partitions is a good idea.

Note

During the installation process, you have an option to encrypt partitions. You must supply a passphrase. This passphrase serves as a key to unlock the bulk encryption key, which is used to secure the partition’s data.

2.3. Restricting network connectivity during the installation process

When installing Red Hat Enterprise Linux 8, the installation medium represents a snapshot of the system at a particular time. Because of this, it may not be up-to-date with the latest security fixes and may be vulnerable to certain issues that were fixed only after the system provided by the installation medium was released.

When installing a potentially vulnerable operating system, always limit exposure only to the closest necessary network zone. The safest choice is the “no network” zone, which means to leave your machine disconnected during the installation process. In some cases, a LAN or intranet connection is sufficient while the Internet connection is the riskiest. To follow the best security practices, choose the closest zone with your repository while installing Red Hat Enterprise Linux 8 from a network.

2.4. Installing the minimum amount of packages required

It is best practice to install only the packages you will use because each piece of software on your computer could possibly contain a vulnerability. If you are installing from the DVD media, take the opportunity to select exactly what packages you want to install during the installation. If you find you need another package, you can always add it to the system later.

2.5. Post-installation procedures

The following steps are the security-related procedures that should be performed immediately after installation of Red Hat Enterprise Linux 8.

Update your system. Enter the following command as root:
```
# yum update
```
Even though the firewall service, firewalld, is automatically enabled with the installation of Red Hat Enterprise Linux, there are scenarios where it might be explicitly disabled, for example in the kickstart configuration. In such a case, it is recommended to consider re-enabling the firewall.
To start firewalld enter the following commands as root:
```
# systemctl start firewalld
# systemctl enable firewalld
```
To enhance security, disable services you do not need. For example, if there are no printers installed on your computer, disable the cups service using the following command:
```
# systemctl disable cups
```
To review active services, enter the following command:
```
$ systemctl list-units | grep service
```

^[1] Since system BIOSes differ between manufacturers, some may not support password protection of either type, while others may support one type but not the other.

Chapter 3. Installing a RHEL 8 system with FIPS mode enabled

To enable the cryptographic module self-checks mandated by the Federal Information Processing Standard (FIPS) Publication 140-2, you have to operate RHEL 8 in FIPS mode.

You can achieve this by:

Starting the installation in FIPS mode.
Switching the system into FIPS mode after the installation.

To avoid cryptographic key material regeneration and reevaluation of the compliance of the resulting system associated with converting already deployed systems, Red Hat recommends starting the installation in FIPS mode.

3.1. Federal Information Processing Standard (FIPS)

The Federal Information Processing Standard (FIPS) Publication 140-2 is a computer security standard developed by the U.S. Government and industry working group to validate the quality of cryptographic modules. See the official FIPS publications at NIST Computer Security Resource Center.

The FIPS 140-2 standard ensures that cryptographic tools implement their algorithms correctly. One of the mechanisms for that is runtime self-checks. See the full FIPS 140-2 standard at FIPS PUB 140-2 for further details and other specifications of the FIPS standard.

To learn about compliance requirements, see the Red Hat Government Standards page.

3.2. Installing the system with FIPS mode enabled

To enable the cryptographic module self-checks mandated by the Federal Information Processing Standard (FIPS) Publication 140-2, enable FIPS mode during the system installation.

Important

Red Hat recommends installing Red Hat Enterprise Linux 8 with FIPS mode enabled, as opposed to enabling FIPS mode later. Enabling FIPS mode during the installation ensures that the system generates all keys with FIPS-approved algorithms and continuous monitoring tests in place.

Procedure

Add the fips=1 option to the kernel command line during the system installation.
During the software selection stage, do not install any third-party software.

After the installation, the system starts in FIPS mode automatically.

Verification

After the system starts, check that FIPS mode is enabled:
```
$ fips-mode-setup --check
FIPS mode is enabled.
```

Additional resources

Editing boot options section in the Performing an advanced RHEL installation

3.3. Additional resources

Chapter 4. Using system-wide cryptographic policies

Crypto policies is a system component that configures the core cryptographic subsystems, covering the TLS, IPSec, SSH, DNSSec, and Kerberos protocols. It provides a small set of policies, which the administrator can select.

4.1. System-wide cryptographic policies

Once a system-wide policy is set up, applications in RHEL follow it and refuse to use algorithms and protocols that do not meet the policy, unless you explicitly request the application to do so. That is, the policy applies to the default behavior of applications when running with the system-provided configuration but you can override it if required so.

Red Hat Enterprise Linux 8 contains the following policy levels:

`DEFAULT`	The default system-wide cryptographic policy level offers secure settings for current threat models. It allows the TLS 1.2 and 1.3 protocols, as well as the IKEv2 and SSH2 protocols. The RSA keys and Diffie-Hellman parameters are accepted if they are at least 2048 bits long.
`LEGACY`	This policy ensures maximum compatibility with Red Hat Enterprise Linux 5 and earlier; it is less secure due to an increased attack surface. In addition to the `DEFAULT` level algorithms and protocols, it includes support for the TLS 1.0 and 1.1 protocols. The algorithms DSA, 3DES, and RC4 are allowed, while RSA keys and Diffie-Hellman parameters are accepted if they are at least 1023 bits long.
`FUTURE`	A conservative security level that is believed to withstand any near-term future attacks. This level does not allow the use of SHA-1 in signature algorithms. The RSA keys and Diffie-Hellman parameters are accepted if they are at least 3072 bits long.
`FIPS`	A policy level that conforms with the FIPS 140-2 requirements. This is used internally by the `fips-mode-setup` tool, which switches the RHEL system into FIPS mode.

Red Hat continuously adjusts all policy levels so that all libraries, except when using the LEGACY policy, provide secure defaults. Even though the LEGACY profile does not provide secure defaults, it does not include any algorithms that are easily exploitable. As such, the set of enabled algorithms or acceptable key sizes in any provided policy may change during the lifetime of the Red Hat Enterprise Linux 8.

Such changes reflect new security standards and new security research. If you must ensure interoperability with a specific system for the whole lifetime of Red Hat Enterprise Linux 8, you should opt-out from cryptographic-policies for components that interact with that system.

Important

Because a cryptographic key used by a certificate on the Customer Portal API does not meet the requirements by the FUTURE system-wide cryptographic policy, the redhat-support-tool utility does not work with this policy level at the moment.

To work around this problem, use the DEFAULT crypto policy while connecting to the Customer Portal API.

Note

The specific algorithms and ciphers described in the policy levels as allowed are available only if an application supports them.

Tool for managing crypto policies

To view or change the current system-wide cryptographic policy, use the update-crypto-policies tool, for example:

$ update-crypto-policies --show
DEFAULT
# update-crypto-policies --set FUTURE
Setting system policy to FUTURE

To ensure that the change of the cryptographic policy is applied, restart the system.

Strong crypto defaults by removing insecure cipher suites and protocols

The following list contains cipher suites and protocols removed from the core cryptographic libraries in Red Hat Enterprise Linux 8. They are not present in the sources, or their support is disabled during the build, so applications cannot use them.

DES (since RHEL 7)
All export grade cipher suites (since RHEL 7)
MD5 in signatures (since RHEL 7)
SSLv2 (since RHEL 7)
SSLv3 (since RHEL 8)
All ECC curves < 224 bits (since RHEL 6)
All binary field ECC curves (since RHEL 6)

Cipher suites and protocols disabled in all policy levels

The following cipher suites and protocols are disabled in all crypto policy levels. They can be enabled only by an explicit configuration of individual applications.

DH with parameters < 1024 bits
RSA with key size < 1024 bits
Camellia
ARIA
SEED
IDEA
Integrity-only cipher suites
TLS CBC mode cipher suites using SHA-384 HMAC
AES-CCM8
All ECC curves incompatible with TLS 1.3, including secp256k1
IKEv1 (since RHEL 8)

Cipher suites and protocols enabled in the crypto-policies levels

The following table shows the enabled cipher suites and protocols in all four crypto-policies levels.

	`LEGACY`	`DEFAULT`	`FIPS`	`FUTURE`
IKEv1	no	no	no	no
3DES	yes	no	no	no
RC4	yes	no	no	no
DH	min. 1024-bit	min. 2048-bit	min. 2048-bit	min. 3072-bit
RSA	min. 1024-bit	min. 2048-bit	min. 2048-bit	min. 3072-bit
DSA	yes	no	no	no
TLS v1.0	yes	no	no	no
TLS v1.1	yes	no	no	no
SHA-1 in digital signatures	yes	yes	no	no
CBC mode ciphers	yes	yes	yes	no^[a]
Symmetric ciphers with keys < 256 bits	yes	yes	yes	no
SHA-1 and SHA-224 signatures in certificates	yes	yes	yes	no
^[a] CBC ciphers are disabled for TLS. In a non-TLS scenario, `AES-128-CBC` is disabled but `AES-256-CBC` is enabled. To disable also `AES-256-CBC`, apply a custom subpolicy.

Additional resources

update-crypto-policies(8) man page

4.2. Switching the system-wide cryptographic policy to mode compatible with earlier releases

The default system-wide cryptographic policy in Red Hat Enterprise Linux 8 does not allow communication using older, insecure protocols. For environments that require to be compatible with Red Hat Enterprise Linux 5 and in some cases also with earlier releases, the less secure LEGACY policy level is available.

Warning

Switching to the LEGACY policy level results in a less secure system and applications.

Procedure

To switch the system-wide cryptographic policy to the LEGACY level, enter the following command as root:
```
# update-crypto-policies --set LEGACY
Setting system policy to LEGACY
```

Additional resources

For the list of available cryptographic policy levels, see the update-crypto-policies(8) man page.

4.3. Switching the system to FIPS mode

The system-wide cryptographic policies contain a policy level that enables cryptographic modules self-checks in accordance with the requirements by the Federal Information Processing Standard (FIPS) Publication 140-2. The fips-mode-setup tool that enables or disables FIPS mode internally uses the FIPS system-wide cryptographic policy level.

Important

Procedure

To switch the system to FIPS mode in RHEL 8:

# fips-mode-setup --enable
Setting system policy to FIPS
FIPS mode will be enabled.
Please reboot the system for the setting to take effect.

Restart your system to allow the kernel to switch to FIPS mode:
```
# reboot
```

Verification

After the restart, you can check the current state of FIPS mode:
```
# fips-mode-setup --check
FIPS mode is enabled.
```

Additional resources

fips-mode-setup(8) man page
List of RHEL 8 applications using cryptography that are not compliant with FIPS 140-2
Security Requirements for Cryptographic Modules on the National Institute of Standards and Technology (NIST) web site.

4.4. Enabling FIPS mode in a container

In RHEL 8.3 and later versions, you do not need to manually enable cryptographic modules self-checks in accordance with the requirements by Federal Information Processing Standard (FIPS) Publication 140-2. On systems with FIPS mode enabled, the podman utility automatically configures containers to FIPS mode.

Note

In RHEL 8, the fips-mode-setup command does not work correctly in containers, and it cannot be used to enable or check FIPS mode in this scenario.

4.4.1. Enabling FIPS mode in a container in RHEL 8.2

In RHEL 8.2 and later versions, you can manually switch a container to FIPS mode by using only a single command in the container. Note that the host system must be in FIPS mode, see Switching the system to FIPS mode.

# mount --bind /usr/share/crypto-policies/back-ends/FIPS /etc/crypto-policies/back-ends

4.4.2. Enabling FIPS mode in a container in RHEL 8.1 and earlier

In RHEL 8.1 and earlier versions, to enable cryptographic modules self-checks in accordance with the requirements by Federal Information Processing Standard (FIPS) Publication 140-2 in a container:

Prerequisites

The host system must be in FIPS mode, see Switching the system to FIPS mode.

Procedure

Mount the /etc/system-fips file on the container from the host.
Set the FIPS cryptographic policy level in the container:
```
$ update-crypto-policies --set FIPS
```

4.5. List of RHEL applications using cryptography that is not compliant with FIPS 140-2

Red Hat recommends to utilize libraries from the core crypto components set, as they are guaranteed to pass all relevant crypto certifications, such as FIPS 140-2, and also follow the RHEL system-wide crypto policies.

See the RHEL 8 core crypto components article for an overview of the RHEL 8 core crypto components, the information on how are they selected, how are they integrated into the operating system, how do they support hardware security modules and smart cards, and how do crypto certifications apply to them.

In addition to the following table, in some RHEL 8 Z-stream releases (for example, 8.1.1), the Firefox browser packages have been updated, and they contain a separate copy of the NSS cryptography library. This way, Red Hat wants to avoid the disruption of rebasing such a low-level component in a patch release. As a result, these Firefox packages do not use a FIPS 140-2-validated module.

Table 4.1. List of RHEL 8 applications using cryptography that is not compliant with FIPS 140-2

Application	Details
FreeRADIUS	The RADIUS protocol uses MD5
ghostscript	Custom cryptogtaphy implementation (MD5, RC4, SHA-2, AES) to encrypt and decrypt documents
Grafana	Cryptographic implementations from the Golang `x/crypto` module (Ed25519, CBC, OCFB, …)
ipxe	Crypto stack for TLS is compiled in, however, it is unused
libica	Software fallbacks for various algorithms such as RSA and ECDH through CPACF instructions
Ovmf (UEFI firmware), Edk2, shim	Full crypto stack (an embedded copy of the OpenSSL library)
perl-Digest-HMAC	HMAC, HMAC-SHA1, HMAC-MD5
perl-Digest-SHA	SHA-1, SHA-224, …
pidgin	DES, RC4
qatengine	Mixed hardware and software implementation of cryptographic primitives (RSA, EC, DH, AES, …)
samba^[a]	AES, DES, RC4
valgrind	AES, hashes^[b]
^[a] Starting with RHEL 8.3, samba uses FIPS-compliant cryptography. ^[b] Re-implements in software hardware-offload operations, such as AES-NI.

4.6. Excluding an application from following system-wide crypto policies

You can customize cryptographic settings used by your application preferably by configuring supported cipher suites and protocols directly in the application.

You can also remove a symlink related to your application from the /etc/crypto-policies/back-ends directory and replace it with your customized cryptographic settings. This configuration prevents the use of system-wide cryptographic policies for applications that use the excluded back end. Furthermore, this modification is not supported by Red Hat.

4.6.1. Examples of opting out of system-wide crypto policies

wget

To customize cryptographic settings used by the wget network downloader, use --secure-protocol and --ciphers options. For example:

$ wget --secure-protocol=TLSv1_1 --ciphers="SECURE128" https://example.com

See the HTTPS (SSL/TLS) Options section of the wget(1) man page for more information.

curl

To specify ciphers used by the curl tool, use the --ciphers option and provide a colon-separated list of ciphers as a value. For example:

$ curl https://example.com --ciphers '@SECLEVEL=0:DES-CBC3-SHA:RSA-DES-CBC3-SHA'

See the curl(1) man page for more information.

Firefox

Even though you cannot opt out of system-wide cryptographic policies in the Firefox web browser, you can further restrict supported ciphers and TLS versions in Firefox’s Configuration Editor. Type about:config in the address bar and change the value of the security.tls.version.min option as required. Setting security.tls.version.min to 1 allows TLS 1.0 as the minimum required, security.tls.version.min 2 enables TLS 1.1, and so on.

OpenSSH

To opt out of the system-wide crypto policies for your OpenSSH server, uncomment the line with the CRYPTO_POLICY= variable in the /etc/sysconfig/sshd file. After this change, values that you specify in the Ciphers, MACs, KexAlgoritms, and GSSAPIKexAlgorithms sections in the /etc/ssh/sshd_config file are not overridden. See the sshd_config(5) man page for more information.

To opt out of system-wide crypto policies for your OpenSSH client, perform one of the following tasks:

For a given user, override the global ssh_config with a user-specific configuration in the ~/.ssh/config file.
For the entire system, specify the crypto policy in a drop-in configuration file located in the /etc/ssh/ssh_config.d/ directory, with a two-digit number prefix smaller than 50, so that it lexicographically precedes the 50-redhat.conf file, and with a .conf suffix, for example, 49-crypto-policy-override.conf.

See the ssh_config(5) man page for more information.

Libreswan

See the Configuring IPsec connections that opt out of the system-wide crypto policies in the Securing networks document for detailed information.

Additional resources

update-crypto-policies(8) man page

4.7. Customizing system-wide cryptographic policies with policy modifiers

Use this procedure to adjust certain algorithms or protocols of any system-wide cryptographic policy level or a full custom policy.

Note

Customization of system-wide cryptographic policies is available from RHEL 8.2.

Procedure

Checkout to the /etc/crypto-policies/policies/modules/ directory:
```
# cd /etc/crypto-policies/policies/modules/
```
Create policy modules for your adjustments, for example:
```
# touch MYCRYPTO1.pmod
# touch NO-AES128.pmod
```
Important
Use upper-case letters in file names of policy modules.

Open the policy modules in a text editor of your choice and insert options that modify the system-wide cryptographic policy, for example:

# vi MYCRYPTO1.pmod

sha1_in_certs = 0
min_rsa_size = 3072

# vi NO-AES128.pmod

cipher = -AES-128-GCM -AES-128-CCM -AES-128-CTR -AES-128-CBC

Save the changes in the module files.
Apply your policy adjustments to the DEFAULT system-wide cryptographic policy level:
```
# update-crypto-policies --set DEFAULT:MYCRYPTO1:NO-AES128
```
To make your cryptographic settings effective for already running services and applications, restart the system:
```
# reboot
```

Additional resources

Custom Policies section in the update-crypto-policies(8) man page and the Crypto Policy Definition Format section in the crypto-policies(7) man page
How to customize crypto policies in RHEL 8.2 Red Hat blog article

4.8. Disabling SHA-1 by customizing a system-wide cryptographic policy

Because the SHA-1 hash function has an inherently weak design, and advancing cryptanalysis has made it vulnerable to attacks, RHEL 8 does not use SHA-1 by default. Nevertheless, some third party applications, for example public signatures, still use SHA-1. To disable the use of SHA-1 in signature algorithms on your system, you can use the NO-SHA1 policy module.

Important

The NO-SHA1 policy module disables the SHA-1 hash function only in signatures and not elsewhere. In particular, the NO-SHA1 module still allows the use of SHA-1 with hash-based message authentication codes (HMAC). This is because HMAC security properties do not rely on collision resistance of the corresponding hash function, and therefore the recent attacks on SHA-1 have a significantly lower impact on the use of SHA-1 for HMAC.

Note

The module for disabling SHA-1 is available from RHEL 8.3. Customization of system-wide cryptographic policies is available from RHEL 8.2.

Procedure

Apply your policy adjustments to the DEFAULT system-wide cryptographic policy level:
```
# update-crypto-policies --set DEFAULT:NO-SHA1
```
To make your cryptographic settings effective for already running services and applications, restart the system:
```
# reboot
```

Additional resources

Custom Policies section in the update-crypto-policies(8) man page.
The Crypto Policy Definition Format section in the crypto-policies(7) man page.
How to customize crypto policies in RHEL 8.2 Red Hat blog article.

4.9. Creating and setting a custom system-wide cryptographic policy

The following steps demonstrate customizing the system-wide cryptographic policies by a complete policy file.

Note

Customization of system-wide cryptographic policies is available from RHEL 8.2.

Procedure

Create a policy file for your customizations:

# cd /etc/crypto-policies/policies/
# touch MYPOLICY.pol

Alternatively, start by copying one of the four predefined policy levels:

# cp /usr/share/crypto-policies/policies/DEFAULT.pol /etc/crypto-policies/policies/MYPOLICY.pol

Edit the file with your custom cryptographic policy in a text editor of your choice to fit your requirements, for example:
```
# vi /etc/crypto-policies/policies/MYPOLICY.pol
```
Switch the system-wide cryptographic policy to your custom level:
```
# update-crypto-policies --set MYPOLICY
```
To make your cryptographic settings effective for already running services and applications, restart the system:
```
# reboot
```

Additional resources

Custom Policies section in the update-crypto-policies(8) man page and the Crypto Policy Definition Format section in the crypto-policies(7) man page
How to customize crypto policies in RHEL 8.2 Red Hat blog article

Chapter 5. Setting a custom cryptographic policy across systems

As an administrator, you can use the Crypto Policies System Role on RHEL to quickly and consistently configure custom cryptographic policies across many different systems using Red Hat Ansible Automation Platform.

5.1. Crypto Policies System Role variables and facts

In a Crypto Policies System Role playbook, you can define the parameters for the crypto policies configuration file according to your preferences and limitations.

If you do not configure any variables, the system role does not configure the system and only reports the facts.

Selected variables for the Crypto Policies System Role

crypto_policies_policy: Determines the cryptographic policy level the system role applies to the managed nodes. For details about the different crypto policy levels, see System-wide cryptographic policies .
crypto_policies_reload: If set to yes, the affected services, currently the ipsec, bind, and sshd services, reload after applying a crypto policy. Defaults to yes.
crypto_policies_reboot_ok: If set to yes, and a reboot is necessary after the system role changes the crypto policy, it sets crypto_policies_reboot_required to yes. Defaults to no.

Facts set by the Crypto Policies System Role

crypto_policies_active: Lists the currently selected policy.
crypto_policies_available_policies: Lists all available policy levels available on the system.
crypto_policies_available_modules: Lists all available subpolicy modules available on the system.

Additional resources

* Creating and setting a custom system-wide cryptographic policy.

5.2. Setting a custom cryptographic policy using the Crypto Policies System Role

You can use the Crypto Policies System Role to configure a large number of managed nodes consistently from a single control node.

Prerequisites

Access and permissions to one or more managed nodes, which are systems you want to configure with the Crypto Policies System Role.
Access and permissions to a control node, which is a system from which Red Hat Ansible Engine configures other systems.
On the control node:
- Red Hat Ansible Engine is installed
- The rhel-system-roles package is installed
- An inventory file which lists the managed nodes.

Procedure

Create a new playbook.yml file with the following content:
```
---
- hosts: all
  tasks:
  - name: Configure crypto policies
    include_role:
      name: linux-system-roles.crypto_policies
    vars:
      - crypto_policies_policy: FUTURE
      - crypto_policies_reboot_ok: true
```
You can replace the FUTURE value with your preferred crypto policy, for example: DEFAULT, LEGACY, and FIPS:OSPP.
The crypto_policies_reboot_ok: true variable causes the system to reboot after the system role changes the crypto policy.
For more details, see Crypto Policies System Role variables and facts .

Optional: Verify playbook syntax.

# ansible-playbook --syntax-check playbook.yml

Run the playbook on your inventory file:

# ansible-playbook -i inventory_file playbook.yml

Verification

On the control node, create another playbook named, for example, verify_playbook.yml:
```
- hosts: all
  tasks:
 - name: Verify active crypto policy
   include_role:
     name: linux-system-roles.crypto_policies

 - debug:
     var: crypto_policies_active
```
This playbook does not change any configurations on the system, only reports the active policy on the managed nodes.

Run the playbook on the same inventory file:

# ansible-playbook -i inventory_file verify_playbook.yml

TASK [debug] **************************
ok: [host] => {
    "crypto_policies_active": "FUTURE"
}

The "crypto_policies_active": variable shows the policy active on the managed node.

5.3. Additional resources

/usr/share/ansible/roles/rhel-system-roles.crypto_policies/README.md file.
ansible-playbook(1) man page.
Installing RHEL System Roles .
Applying a system role .

Chapter 6. Configuring applications to use cryptographic hardware through PKCS #11

Separating parts of your secret information on dedicated cryptographic devices, such as smart cards and cryptographic tokens for end-user authentication and hardware security modules (HSM) for server applications, provides an additional layer of security. In Red Hat Enterprise Linux 8, support for cryptographic hardware through the PKCS #11 API is consistent across different applications, and the isolation of secrets on cryptographic hardware is not a complicated task.

6.1. Cryptographic hardware support through PKCS #11

PKCS #11 (Public-Key Cryptography Standard) defines an application programming interface (API) to cryptographic devices that hold cryptographic information and perform cryptographic functions. These devices are called tokens, and they can be implemented in a hardware or software form.

A PKCS #11 token can store various object types including a certificate; a data object; and a public, private, or secret key. These objects are uniquely identifiable through the PKCS #11 URI scheme.

A PKCS #11 URI is a standard way to identify a specific object in a PKCS #11 module according to the object attributes. This enables you to configure all libraries and applications with the same configuration string in the form of a URI.

Red Hat Enterprise Linux 8 provides the OpenSC PKCS #11 driver for smart cards by default. However, hardware tokens and HSMs can have their own PKCS #11 modules that do not have their counterpart in Red Hat Enterprise Linux. You can register such PKCS #11 modules with the p11-kit tool, which acts as a wrapper over the registered smart card drivers in the system.

To make your own PKCS #11 module work on the system, add a new text file to the /etc/pkcs11/modules/ directory

You can add your own PKCS #11 module into the system by creating a new text file in the /etc/pkcs11/modules/ directory. For example, the OpenSC configuration file in p11-kit looks as follows:

$ cat /usr/share/p11-kit/modules/opensc.module
module: opensc-pkcs11.so

Additional resources

6.2. Using SSH keys stored on a smart card

Red Hat Enterprise Linux enables you to use RSA and ECDSA keys stored on a smart card on OpenSSH clients. Use this procedure to enable authentication using a smart card instead of using a password.

Prerequisites

On the client side, the opensc package is installed and the pcscd service is running.

Procedure

List all keys provided by the OpenSC PKCS #11 module including their PKCS #11 URIs and save the output to the keys.pub file:

$ ssh-keygen -D pkcs11: > keys.pub
$ ssh-keygen -D pkcs11:
ssh-rsa AAAAB3NzaC1yc2E...KKZMzcQZzx pkcs11:id=%02;object=SIGN%20pubkey;token=SSH%20key;manufacturer=piv_II?module-path=/usr/lib64/pkcs11/opensc-pkcs11.so
ecdsa-sha2-nistp256 AAA...J0hkYnnsM= pkcs11:id=%01;object=PIV%20AUTH%20pubkey;token=SSH%20key;manufacturer=piv_II?module-path=/usr/lib64/pkcs11/opensc-pkcs11.so

To enable authentication using a smart card on a remote server (example.com), transfer the public key to the remote server. Use the ssh-copy-id command with keys.pub created in the previous step:
```
$ ssh-copy-id -f -i keys.pub username@example.com
```
To connect to example.com using the ECDSA key from the output of the ssh-keygen -D command in step 1, you can use just a subset of the URI, which uniquely references your key, for example:
```
$ ssh -i "pkcs11:id=%01?module-path=/usr/lib64/pkcs11/opensc-pkcs11.so" example.com
Enter PIN for 'SSH key':
[example.com] $
```

You can use the same URI string in the ~/.ssh/config file to make the configuration permanent:

$ cat ~/.ssh/config
IdentityFile "pkcs11:id=%01?module-path=/usr/lib64/pkcs11/opensc-pkcs11.so"
$ ssh example.com
Enter PIN for 'SSH key':
[example.com] $

Because OpenSSH uses the p11-kit-proxy wrapper and the OpenSC PKCS #11 module is registered to PKCS#11 Kit, you can simplify the previous commands:

$ ssh -i "pkcs11:id=%01" example.com
Enter PIN for 'SSH key':
[example.com] $

If you skip the id= part of a PKCS #11 URI, OpenSSH loads all keys that are available in the proxy module. This can reduce the amount of typing required:

$ ssh -i pkcs11: example.com
Enter PIN for 'SSH key':
[example.com] $

Additional resources

Fedora 28: Better smart card support in OpenSSH.
p11-kit(8), opensc.conf(5), pcscd(8), ssh(1), and ssh-keygen(1) man pages.

6.3. Configuring applications to authenticate using certificates from smart cards

The wget network downloader enables you to specify PKCS #11 URIs instead of paths to locally stored private keys, and thus simplifies creating scripts for tasks that require safely stored private keys and certificates. For example:
```
$ wget --private-key 'pkcs11:token=softhsm;id=%01;type=private?pin-value=111111' --certificate 'pkcs11:token=softhsm;id=%01;type=cert' https://example.com/
```
See the wget(1) man page for more information.

Specifying PKCS #11 URI for use by the curl tool is analogous:

$ curl --key 'pkcs11:token=softhsm;id=%01;type=private?pin-value=111111' --cert 'pkcs11:token=softhsm;id=%01;type=cert' https://example.com/

See the curl(1) man page for more information.

The Firefox web browser automatically loads the p11-kit-proxy module. This means that every supported smart card in the system is automatically detected. For using TLS client authentication, no additional setup is required and keys from a smart card are automatically used when a server requests them.

Using PKCS #11 URIs in custom applications

If your application uses the GnuTLS or NSS library, support for PKCS #11 URIs is ensured by their built-in support for PKCS #11. Also, applications relying on the OpenSSL library can access cryptographic hardware modules thanks to the openssl-pkcs11 engine.

With applications that require working with private keys on smart cards and that do not use NSS, GnuTLS, and OpenSSL, use p11-kit to implement registering PKCS #11 modules.

Additional resources

p11-kit(8) man page.

6.4. Using HSMs protecting private keys in Apache

The Apache HTTP server can work with private keys stored on hardware security modules (HSMs), which helps to prevent the keys' disclosure and man-in-the-middle attacks. Note that this usually requires high-performance HSMs for busy servers.

For secure communication in the form of the HTTPS protocol, the Apache HTTP server (httpd) uses the OpenSSL library. OpenSSL does not support PKCS #11 natively. To utilize HSMs, you have to install the openssl-pkcs11 package, which provides access to PKCS #11 modules through the engine interface. You can use a PKCS #11 URI instead of a regular file name to specify a server key and a certificate in the /etc/httpd/conf.d/ssl.conf configuration file, for example:

SSLCertificateFile    "pkcs11:id=%01;token=softhsm;type=cert"
SSLCertificateKeyFile "pkcs11:id=%01;token=softhsm;type=private?pin-value=111111"

Install the httpd-manual package to obtain complete documentation for the Apache HTTP Server, including TLS configuration. The directives available in the /etc/httpd/conf.d/ssl.conf configuration file are described in detail in /usr/share/httpd/manual/mod/mod_ssl.html.

6.5. Using HSMs protecting private keys in Nginx

The Nginx HTTP server can work with private keys stored on hardware security modules (HSMs), which helps to prevent the keys' disclosure and man-in-the-middle attacks. Note that this usually requires high-performance HSMs for busy servers.

Because Nginx also uses the OpenSSL for cryptographic operations, support for PKCS #11 must go through the openssl-pkcs11 engine. Nginx currently supports only loading private keys from an HSM, and a certificate must be provided separately as a regular file. Modify the ssl_certificate and ssl_certificate_key options in the server section of the /etc/nginx/nginx.conf configuration file:

ssl_certificate     /path/to/cert.pem
ssl_certificate_key "engine:pkcs11:pkcs11:token=softhsm;id=%01;type=private?pin-value=111111";

Note that the engine:pkcs11: prefix is needed for the PKCS #11 URI in the Nginx configuration file. This is because the other pkcs11 prefix refers to the engine name.

Chapter 7. Using shared system certificates

The shared system certificates storage enables NSS, GnuTLS, OpenSSL, and Java to share a default source for retrieving system certificate anchors and block-list information. By default, the trust store contains the Mozilla CA list, including positive and negative trust. The system allows updating the core Mozilla CA list or choosing another certificate list.

7.1. The system-wide trust store

In Red Hat Enterprise Linux, the consolidated system-wide trust store is located in the /etc/pki/ca-trust/ and /usr/share/pki/ca-trust-source/ directories. The trust settings in /usr/share/pki/ca-trust-source/ are processed with lower priority than settings in /etc/pki/ca-trust/.

Certificate files are treated depending on the subdirectory they are installed to the following directories:

for trust anchors
- /usr/share/pki/ca-trust-source/anchors/ or
- /etc/pki/ca-trust/source/anchors/
for distrusted certificates
- /usr/share/pki/ca-trust-source/blacklist/ or
- /etc/pki/ca-trust/source/blacklist/
for certificates in the extended BEGIN TRUSTED file format
- /usr/share/pki/ca-trust-source/ or
- /etc/pki/ca-trust/source/

Note

In a hierarchical cryptographic system, a trust anchor is an authoritative entity which other parties consider being trustworthy. In the X.509 architecture, a root certificate is a trust anchor from which a chain of trust is derived. To enable chain validation, the trusting party must have access to the trust anchor first.

7.2. Adding new certificates

To acknowledge applications on your system with a new source of trust, add the corresponding certificate to the system-wide store, and use the update-ca-trust command.

Prerequisites

The ca-certificates package is present on the system.

Procedure

To add a certificate in the simple PEM or DER file formats to the list of CAs trusted on the system, copy the certificate file to the /usr/share/pki/ca-trust-source/anchors/ or /etc/pki/ca-trust/source/anchors/ directory, for example:
```
# cp ~/certificate-trust-examples/Cert-trust-test-ca.pem /usr/share/pki/ca-trust-source/anchors/
```
To update the system-wide trust store configuration, use the update-ca-trust command:
```
# update-ca-trust
```

Note

While the Firefox browser is able to use an added certificate without executing update-ca-trust, Red Hat recommends to use the update-ca-trust command after a CA change. Also note that browsers, such as Firefox, Epiphany, or Chromium, cache files, and you might have to clear browser’s cache or restart your browser to load the current system certificates configuration.

7.3. Managing trusted system certificates

The trust command provides a convenient way for managing certificates in the shared system-wide trust store.

To list, extract, add, remove, or change trust anchors, use the trust command. To see the built-in help for this command, enter it without any arguments or with the --help directive:

$ trust
usage: trust command <args>...

Common trust commands are:
  list             List trust or certificates
  extract          Extract certificates and trust
  extract-compat   Extract trust compatibility bundles
  anchor           Add, remove, change trust anchors
  dump             Dump trust objects in internal format

See 'trust <command> --help' for more information

To list all system trust anchors and certificates, use the trust list command:

$ trust list
pkcs11:id=%d2%87%b4%e3%df%37%27%93%55%f6%56%ea%81%e5%36%cc%8c%1e%3f%bd;type=cert
    type: certificate
    label: ACCVRAIZ1
    trust: anchor
    category: authority

pkcs11:id=%a6%b3%e1%2b%2b%49%b6%d7%73%a1%aa%94%f5%01%e7%73%65%4c%ac%50;type=cert
    type: certificate
    label: ACEDICOM Root
    trust: anchor
    category: authority
...

To store a trust anchor into the system-wide trust store, use the trust anchor sub-command and specify a path to a certificate. Replace path.to/certificate.crt by a path to your certificate and its file name:
```
# trust anchor path.to/certificate.crt
```

To remove a certificate, use either a path to a certificate or an ID of a certificate:

# trust anchor --remove path.to/certificate.crt
# trust anchor --remove "pkcs11:id=%AA%BB%CC%DD%EE;type=cert"

Additional resources

All sub-commands of the trust commands offer a detailed built-in help, for example:

$ trust list --help
usage: trust list --filter=<what>

  --filter=<what>     filter of what to export
                        ca-anchors        certificate anchors
...
  --purpose=<usage>   limit to certificates usable for the purpose
                        server-auth       for authenticating servers
...

7.4. Additional resources

update-ca-trust(8) and trust(1) man pages

Chapter 8. Scanning the system for configuration compliance and vulnerabilities

A compliance audit is a process of determining whether a given object follows all the rules specified in a compliance policy. The compliance policy is defined by security professionals who specify the required settings, often in the form of a checklist, that a computing environment should use.

Compliance policies can vary substantially across organizations and even across different systems within the same organization. Differences among these policies are based on the purpose of each system and its importance for the organization. Custom software settings and deployment characteristics also raise a need for custom policy checklists.

8.1. Configuration compliance tools in RHEL

Red Hat Enterprise Linux provides tools that enable you to perform a fully automated compliance audit. These tools are based on the Security Content Automation Protocol (SCAP) standard and are designed for automated tailoring of compliance policies.

SCAP Workbench - The scap-workbench graphical utility is designed to perform configuration and vulnerability scans on a single local or remote system. You can also use it to generate security reports based on these scans and evaluations.
OpenSCAP - The OpenSCAP library, with the accompanying oscap command-line utility, is designed to perform configuration and vulnerability scans on a local system, to validate configuration compliance content, and to generate reports and guides based on these scans and evaluations.
SCAP Security Guide (SSG) - The scap-security-guide package provides the latest collection of security policies for Linux systems. The guidance consists of a catalog of practical hardening advice, linked to government requirements where applicable. The project bridges the gap between generalized policy requirements and specific implementation guidelines.
Script Check Engine (SCE) - SCE is an extension to the SCAP protocol that enables administrators to write their security content using a scripting language, such as Bash, Python, and Ruby. The SCE extension is provided in the openscap-engine-sce package. The SCE itself is not part of the SCAP standard.

To perform automated compliance audits on multiple systems remotely, you can use the OpenSCAP solution for Red Hat Satellite.

Additional resources

oscap(8), scap-workbench(8), and scap-security-guide(8) man pages
Red Hat Security Demos: Creating Customized Security Policy Content to Automate Security Compliance
Red Hat Security Demos: Defend Yourself with RHEL Security Technologies
Security Compliance Management in the Administering Red Hat Satellite Guide.

8.2. Vulnerability scanning

8.2.1. Red Hat Security Advisories OVAL feed

Red Hat Enterprise Linux security auditing capabilities are based on the Security Content Automation Protocol (SCAP) standard. SCAP is a multi-purpose framework of specifications that supports automated configuration, vulnerability and patch checking, technical control compliance activities, and security measurement.

SCAP specifications create an ecosystem where the format of security content is well-known and standardized although the implementation of the scanner or policy editor is not mandated. This enables organizations to build their security policy (SCAP content) once, no matter how many security vendors they employ.

The Open Vulnerability Assessment Language (OVAL) is the essential and oldest component of SCAP. Unlike other tools and custom scripts, OVAL describes a required state of resources in a declarative manner. OVAL code is never executed directly but using an OVAL interpreter tool called scanner. The declarative nature of OVAL ensures that the state of the assessed system is not accidentally modified.

Like all other SCAP components, OVAL is based on XML. The SCAP standard defines several document formats. Each of them includes a different kind of information and serves a different purpose.

Red Hat Product Security helps customers evaluate and manage risk by tracking and investigating all security issues affecting Red Hat customers. It provides timely and concise patches and security advisories on the Red Hat Customer Portal. Red Hat creates and supports OVAL patch definitions, providing machine-readable versions of our security advisories.

Because of differences between platforms, versions, and other factors, Red Hat Product Security qualitative severity ratings of vulnerabilities do not directly align with the Common Vulnerability Scoring System (CVSS) baseline ratings provided by third parties. Therefore, we recommend that you use the RHSA OVAL definitions instead of those provided by third parties.

The RHSA OVAL definitions are available individually and as a complete package, and are updated within an hour of a new security advisory being made available on the Red Hat Customer Portal.

Each OVAL patch definition maps one-to-one to a Red Hat Security Advisory (RHSA). Because an RHSA can contain fixes for multiple vulnerabilities, each vulnerability is listed separately by its Common Vulnerabilities and Exposures (CVE) name and has a link to its entry in our public bug database.

The RHSA OVAL definitions are designed to check for vulnerable versions of RPM packages installed on a system. It is possible to extend these definitions to include further checks, for example, to find out if the packages are being used in a vulnerable configuration. These definitions are designed to cover software and updates shipped by Red Hat. Additional definitions are required to detect the patch status of third-party software.

Additional resources

8.2.2. Scanning the system for vulnerabilities

The oscap command-line utility enables you to scan local systems, validate configuration compliance content, and generate reports and guides based on these scans and evaluations. This utility serves as a front end to the OpenSCAP library and groups its functionalities to modules (sub-commands) based on the type of SCAP content it processes.

Prerequisites

The AppStream repository is enabled.

Procedure

Install the openscap-scanner and bzip2 packages:
```
# yum install openscap-scanner bzip2
```

Download the latest RHSA OVAL definitions for your system:

# wget -O - https://www.redhat.com/security/data/oval/v2/RHEL8/rhel-8.oval.xml.bz2 | bzip2 --decompress > rhel-8.oval.xml

Scan the system for vulnerabilities and save results to the vulnerability.html file:
```
# oscap oval eval --report vulnerability.html rhel-8.oval.xml
```

Verification

Check the results in a browser of your choice, for example:
```
$ firefox vulnerability.html &
```

Additional resources

oscap(8) man page
Red Hat OVAL definitions

8.2.3. Scanning remote systems for vulnerabilities

You can check also remote systems for vulnerabilities with the OpenSCAP scanner using the oscap-ssh tool over the SSH protocol.

Prerequisites

The AppStream repository is enabled.
The openscap-scanner package is installed on the remote systems.
The SSH server is running on the remote systems.

Procedure

Install the openscap-utils and bzip2 packages:
```
# yum install openscap-utils bzip2
```

Download the latest RHSA OVAL definitions for your system:

# wget -O - https://www.redhat.com/security/data/oval/v2/RHEL8/rhel-8.oval.xml.bz2 | bzip2 --decompress > rhel-8.oval.xml

Scan a remote system with the machine1 host name, SSH running on port 22, and the joesec user name for vulnerabilities and save results to the remote-vulnerability.html file:
```
# oscap-ssh joesec@machine1 22 oval eval --report remote-vulnerability.html rhel-8.oval.xml
```

Additional resources

oscap-ssh(8)
Red Hat OVAL definitions

8.3. Configuration compliance scanning

8.3.1. Configuration compliance in RHEL 8

You can use configuration compliance scanning to conform to a baseline defined by a specific organization. For example, if you work with the US government, you might have to comply with the Operating System Protection Profile (OSPP), and if you are a payment processor, you might have to be compliant with the Payment Card Industry Data Security Standard (PCI-DSS). You can also perform configuration compliance scanning to harden your system security.

Red Hat recommends you follow the Security Content Automation Protocol (SCAP) content provided in the SCAP Security Guide package because it is in line with Red Hat best practices for affected components.

The SCAP Security Guide package provides content which conforms to the SCAP 1.2 and SCAP 1.3 standards. The openscap scanner utility is compatible with both SCAP 1.2 and SCAP 1.3 content provided in the SCAP Security Guide package.

Important

Performing a configuration compliance scanning does not guarantee the system is compliant.

The SCAP Security Guide suite provides profiles for several platforms in a form of data stream documents. A data stream is a file that contains definitions, benchmarks, profiles, and individual rules. Each rule specifies the applicability and requirements for compliance. RHEL 8 provides several profiles for compliance with security policies. In addition to the industry standard, Red Hat data streams also contain information for remediation of failed rules.

Structure of compliance scanning resources

Data stream
   ├── xccdf
   |      ├── benchmark
   |            ├── profile
   |            |    ├──rule reference
   |            |    └──variable
   |            ├── rule
   |                 ├── human readable data
   |                 ├── oval reference
   ├── oval          ├── ocil reference
   ├── ocil          ├── cpe reference
   └── cpe           └── remediation

A profile is a set of rules based on a security policy, such as OSPP, PCI-DSS, and Health Insurance Portability and Accountability Act (HIPAA). This enables you to audit the system in an automated way for compliance with security standards.

You can modify (tailor) a profile to customize certain rules, for example, password length. For more information on profile tailoring, see Customizing a security profile with SCAP Workbench.

8.3.2. Possible results of an OpenSCAP scan

Depending on various properties of your system and the data stream and profile applied to an OpenSCAP scan, each rule may produce a specific result. This is a list of possible results with brief explanations of what they mean.

Table 8.1. Possible results of an OpenSCAP scan

Result	Explanation
Pass	The scan did not find any conflicts with this rule.
Fail	The scan found a conflict with this rule.
Not checked	OpenSCAP does not perform an automatic evaluation of this rule. Check whether your system conforms to this rule manually.
Not applicable	This rule does not apply to the current configuration.
Not selected	This rule is not part of the profile. OpenSCAP does not evaluate this rule and does not display these rules in the results.
Error	The scan encountered an error. For additional information, you can enter the `oscap` command with the `--verbose DEVEL` option. Consider opening a bug report.
Unknown	The scan encountered an unexpected situation. For additional information, you can enter the `oscap` command with the `--verbose DEVEL option. Consider opening a bug report.

8.3.3. Viewing profiles for configuration compliance

Before you decide to use profiles for scanning or remediation, you can list them and check their detailed descriptions using the oscap info sub-command.

Prerequisites

The openscap-scanner and scap-security-guide packages are installed.

Procedure

List all available files with security compliance profiles provided by the SCAP Security Guide project:

$ ls /usr/share/xml/scap/ssg/content/
ssg-firefox-cpe-dictionary.xml  ssg-rhel6-ocil.xml
ssg-firefox-cpe-oval.xml        ssg-rhel6-oval.xml
...
ssg-rhel6-ds-1.2.xml          ssg-rhel8-oval.xml
ssg-rhel8-ds.xml              ssg-rhel8-xccdf.xml
...

Display detailed information about a selected data stream using the oscap info sub-command. XML files containing data streams are indicated by the -ds string in their names. In the Profiles section, you can find a list of available profiles and their IDs:

$ oscap info /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
...
Profiles:
  Title: Health Insurance Portability and Accountability Act (HIPAA)
    Id: xccdf_org.ssgproject.content_profile_hipaa
  Title: PCI-DSS v3.2.1 Control Baseline for Red Hat Enterprise Linux 8
    Id: xccdf_org.ssgproject.content_profile_pci-dss
  Title: OSPP - Protection Profile for General Purpose Operating Systems
    Id: xccdf_org.ssgproject.content_profile_ospp
...

Select a profile from the data-stream file and display additional details about the selected profile. To do so, use oscap info with the --profile option followed by the last section of the ID displayed in the output of the previous command. For example, the ID of the HIPPA profile is: xccdf_org.ssgproject.content_profile_hipaa, and the value for the --profile option is hipaa:

$ oscap info --profile hipaa /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
...
Profile
	Title: Health Insurance Portability and Accountability Act (HIPAA)

	Description: The HIPAA Security Rule establishes U.S. national standards to protect individuals’ electronic personal health information that is created, received, used, or maintained by a covered entity.
...

Additional resources

scap-security-guide(8) man page

8.3.4. Assessing configuration compliance with a specific baseline

To determine whether your system conforms to a specific baseline, follow these steps.

Prerequisites

The openscap-scanner and scap-security-guide packages are installed
You know the ID of the profile within the baseline with which the system should comply. To find the ID, see Viewing Profiles for Configuration Compliance.

Procedure

Evaluate the compliance of the system with the selected profile and save the scan results in the report.html HTML file, for example:
```
$ sudo oscap xccdf eval --report report.html --profile hipaa /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
```
Optional: Scan a remote system with the machine1 host name, SSH running on port 22, and the joesec user name for compliance and save results to the remote-report.html file:
```
$ oscap-ssh joesec@machine1 22 xccdf eval --report remote_report.html --profile hipaa /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
```

Additional resources

scap-security-guide(8) man page
SCAP Security Guide documentation in the file:///usr/share/doc/scap-security-guide/ directory
Guide to the Secure Configuration of Red Hat Enterprise Linux 8 installed with the scap-security-guide-doc package

8.4. Remediating the system to align with a specific baseline

Use this procedure to remediate the RHEL 8 system to align with a specific baseline. This example uses the Health Insurance Portability and Accountability Act (HIPAA) profile.

Warning

If not used carefully, running the system evaluation with the Remediate option enabled might render the system non-functional. Red Hat does not provide any automated method to revert changes made by security-hardening remediations. Remediations are supported on RHEL systems in the default configuration. If your system has been altered after the installation, running remediation might not make it compliant with the required security profile.

Prerequisites

The scap-security-guide package is installed on your RHEL 8 system.

Procedure

Use the oscap command with the --remediate option:

$ sudo oscap xccdf eval --profile hipaa --remediate /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml

Restart your system.

Verification

Evaluate compliance of the system with the HIPAA profile, and save scan results in the hipaa_report.html file:

$ oscap xccdf eval --report hipaa_report.html --profile hipaa /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml

Additional resources

scap-security-guide(8) and oscap(8) man pages

8.5. Remediating the system to align with a specific baseline using the SSG Ansible playbook

Use this procedure to remediate your system with a specific baseline using the Ansible playbook file from the SCAP Security Guide project. This example uses the Health Insurance Portability and Accountability Act (HIPAA) profile.

Warning

Prerequisites

The scap-security-guide package is installed on your RHEL 8 system.
The ansible package is installed. See the Ansible Installation Guide for more information.

Procedure

Remediate your system to align with HIPAA using Ansible:

# ansible-playbook -i localhost, -c local /usr/share/scap-security-guide/ansible/rhel8-playbook-hipaa.yml

Restart the system.

Verification

Evaluate compliance of the system with the HIPAA profile, and save scan results in the hipaa_report.html file:

# oscap xccdf eval --profile hipaa --report hipaa_report.html /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml

Additional resources

scap-security-guide(8) and oscap(8) man pages
Ansible Documentation

8.6. Creating a remediation Ansible playbook to align the system with a specific baseline

You can create an Ansible playbook containing only the remediations that are required to align your system with a specific baseline. This example uses the Health Insurance Portability and Accountability Act (HIPAA) profile. With this procedure, you create a smaller playbook that does not cover already satisfied requirements. By following these steps, you do not modify your system in any way, you only prepare a file for later application.

Prerequisites

The scap-security-guide package is installed on your RHEL 8 system.

Procedure

Scan the system and save the results:

# oscap xccdf eval --profile hipaa --results hipaa-results.xml /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml

Generate an Ansible playbook based on the file generated in the previous step:

# oscap xccdf generate fix --fix-type ansible --output hipaa-remediations.yml hipaa-results.xml

The hipaa-remediations.yml file contains Ansible remediations for rules that failed during the scan performed in step 1. After reviewing this generated file, you can apply it with the ansible-playbook hipaa-remediations.yml command.

Verification

In a text editor of your choice, review that the hipaa-remediations.yml file contains rules that failed in the scan performed in step 1.

Additional resources

scap-security-guide(8) and oscap(8) man pages
Ansible Documentation

8.7. Creating a remediation Bash script for a later application

Use this procedure to create a Bash script containing remediations that align your system with a security profile such as HIPAA. Using the following steps, you do not do any modifications to your system, you only prepare a file for later application.

Prerequisites

The scap-security-guide package is installed on your RHEL 8 system.

Procedure

Use the oscap command to scan the system and to save the results to an XML file. In the following example, oscap evaluates the system against the hipaa profile:
```
# oscap xccdf eval --profile hipaa --results hipaa-results.xml /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
```

Generate a Bash script based on the results file generated in the previous step:

# oscap xccdf generate fix --profile hipaa --fix-type bash --output hipaa-remediations.sh hipaa-results.xml

The hipaa-remediations.sh file contains remediations for rules that failed during the scan performed in step 1. After reviewing this generated file, you can apply it with the ./hipaa-remediations.sh command when you are in the same directory as this file.

Verification

In a text editor of your choice, review that the hipaa-remediations.sh file contains rules that failed in the scan performed in step 1.

Additional resources

scap-security-guide(8), oscap(8), and bash(1) man pages

8.8. Scanning the system with a customized profile using SCAP Workbench

SCAP Workbench, which is contained in the scap-workbench package, is a graphical utility that enables users to perform configuration and vulnerability scans on a single local or a remote system, perform remediation of the system, and generate reports based on scan evaluations. Note that SCAP Workbench has limited functionality compared with the oscap command-line utility. SCAP Workbench processes security content in the form of data-stream files.

8.8.1. Using SCAP Workbench to scan and remediate the system

To evaluate your system against the selected security policy, use the following procedure.

Prerequisites

The scap-workbench package is installed on your system.

Procedure

To run SCAP Workbench from the GNOME Classic desktop environment, press the Super key to enter the Activities Overview, type scap-workbench, and then press Enter. Alternatively, use:
```
$ scap-workbench &
```
Select a security policy using either of the following options:
- Load Content button on the starting window
- Open content from SCAP Security Guide
- Open Other Content in the File menu, and search the respective XCCDF, SCAP RPM, or data stream file.
You can allow automatic correction of the system configuration by selecting the Remediate check box. With this option enabled, SCAP Workbench attempts to change the system configuration in accordance with the security rules applied by the policy. This process should fix the related checks that fail during the system scan.
Warning
If not used carefully, running the system evaluation with the Remediate option enabled might render the system non-functional. Red Hat does not provide any automated method to revert changes made by security-hardening remediations. Remediations are supported on RHEL systems in the default configuration. If your system has been altered after the installation, running remediation might not make it compliant with the required security profile.
Scan your system with the selected profile by clicking the Scan button.
To store the scan results in form of an XCCDF, ARF, or HTML file, click the Save Results combo box. Choose the HTML Report option to generate the scan report in human-readable format. The XCCDF and ARF (data stream) formats are suitable for further automatic processing. You can repeatedly choose all three options.
To export results-based remediations to a file, use the Generate remediation role pop-up menu.

8.8.2. Customizing a security profile with SCAP Workbench

You can customize a security profile by changing parameters in certain rules (for example, minimum password length), removing rules that you cover in a different way, and selecting additional rules, to implement internal policies. You cannot define new rules by customizing a profile.

The following procedure demonstrates the use of SCAP Workbench for customizing (tailoring) a profile. You can also save the tailored profile for use with the oscap command-line utility.

Prerequisites

The scap-workbench package is installed on your system.

Procedure

Run SCAP Workbench, and select the profile to customize by using either Open content from SCAP Security Guide or Open Other Content in the File menu.
To adjust the selected security profile according to your needs, click the Customize button.
This opens the new Customization window that enables you to modify the currently selected profile without changing the original data stream file. Choose a new profile ID.
Find a rule to modify using either the tree structure with rules organized into logical groups or the Search field.
Include or exclude rules using check boxes in the tree structure, or modify values in rules where applicable.
Confirm the changes by clicking the OK button.
To store your changes permanently, use one of the following options:
- Save a customization file separately by using Save Customization Only in the File menu.
- Save all security content at once by Save All in the File menu.
  If you select the Into a directory option, SCAP Workbench saves both the data stream file and the customization file to the specified location. You can use this as a backup solution.
  By selecting the As RPM option, you can instruct SCAP Workbench to create an RPM package containing the data stream file and the customization file. This is useful for distributing the security content to systems that cannot be scanned remotely, and for delivering the content for further processing.

Note

Because SCAP Workbench does not support results-based remediations for tailored profiles, use the exported remediations with the oscap command-line utility.

8.9. Deploying systems that are compliant with a security profile immediately after an installation

You can use the OpenSCAP suite to deploy RHEL systems that are compliant with a security profile, such as OSPP, PCI-DSS, and HIPAA profile, immediately after the installation process. Using this deployment method, you can apply specific rules that cannot be applied later using remediation scripts, for example, a rule for password strength and partitioning.

8.9.1. Deploying baseline-compliant RHEL systems using the graphical installation

Use this procedure to deploy a RHEL system that is aligned with a specific baseline. This example uses Protection Profile for General Purpose Operating System (OSPP).

Prerequisites

You have booted into the graphical installation program. Note that the OSCAP Anaconda Add-on does not support text-only installation.
You have accessed the Installation Summary window.

Procedure

From the Installation Summary window, click Software Selection. The Software Selection window opens.
From the Base Environment pane, select the Server environment. You can select only one base environment.
Warning
Do not use the Server with GUI base environment if you want to deploy a compliant system. Security profiles provided as part of the SCAP Security Guide may not be compatible with the extended package set of Server with GUI. For more information, see, for example, BZ#1648162, BZ#1787156, or BZ#1816199.
Click Done to apply the setting and return to the Installation Summary window.
Click Security Policy. The Security Policy window opens.
To enable security policies on the system, toggle the Apply security policy switch to ON.
Select Protection Profile for General Purpose Operating Systems from the profile pane.
Click Select Profile to confirm the selection.
Confirm the changes in the Changes that were done or need to be done pane that is displayed at the bottom of the window. Complete any remaining manual changes.
Because OSPP has strict partitioning requirements that must be met, create separate partitions for /boot, /home, /var, /var/log, /var/tmp, and /var/log/audit.
Complete the graphical installation process.
Note
The graphical installation program automatically creates a corresponding Kickstart file after a successful installation. You can use the /root/anaconda-ks.cfg file to automatically install OSPP-compliant systems.

Verification

To check the current status of the system after installation is complete, reboot the system and start a new scan:

# oscap xccdf eval --profile ospp --report eval_postinstall_report.html /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml

Additional resources

For more details on partitioning, see Configuring manual partitioning.

8.9.2. Deploying baseline-compliant RHEL systems using Kickstart

Use this procedure to deploy RHEL systems that are aligned with a specific baseline. This example uses Protection Profile for General Purpose Operating System (OSPP).

Prerequisites

The scap-security-guide package is installed on your RHEL 8 system.

Procedure

Open the /usr/share/scap-security-guide/kickstarts/ssg-rhel8-ospp-ks.cfg Kickstart file in an editor of your choice.
Update the partitioning scheme to fit your configuration requirements. For OSPP compliance, the separate partitions for /boot, /home, /var, /var/log, /var/tmp, and /var/log/audit must be preserved, and you can only change the size of the partitions.
Warning
Because the OSCAP Anaconda Addon plugin does not support text-only installation, do not use the text option in your Kickstart file. For more information, see RHBZ#1674001.
Start a Kickstart installation as described in Performing an automated installation using Kickstart.

Important

Passwords in the hash form cannot be checked for OSPP requirements.

Verification

To check the current status of the system after installation is complete, reboot the system and start a new scan:

# oscap xccdf eval --profile ospp --report eval_postinstall_report.html /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml

Additional resources

For more details, see the OSCAP Anaconda Addon project page.

8.10. Scanning container and container images for vulnerabilities

Use this procedure to find security vulnerabilities in a container or a container image.

Note

The oscap-podman command is available from RHEL 8.2. For RHEL 8.1 and 8.0, use the workaround described in the Using OpenSCAP for scanning containers in RHEL 8 Knowledgebase article.

Prerequisites

The openscap-utils package is installed.

Procedure

Download the latest RHSA OVAL definitions for your system:

# wget -O - https://www.redhat.com/security/data/oval/v2/RHEL8/rhel-8.oval.xml.bz2 | bzip2 --decompress > rhel-8.oval.xml

Get the ID of a container or a container image, for example:

# podman images
REPOSITORY                            TAG      IMAGE ID       CREATED       SIZE
registry.access.redhat.com/ubi8/ubi   latest   096cae65a207   7 weeks ago   239 MB

Scan the container or the container image for vulnerabilities and save results to the vulnerability.html file:
```
# oscap-podman 096cae65a207 oval eval --report vulnerability.html rhel-8.oval.xml
```
Note that the oscap-podman command requires root privileges, and the ID of a container is the first argument.

Verification

Check the results in a browser of your choice, for example:
```
$ firefox vulnerability.html &
```

Additional resources

For more information, see the oscap-podman(8) and oscap(8) man pages.

8.11. Assessing security compliance of a container or a container image with a specific baseline

Follow these steps to assess compliance of your container or a container image with a specific security baseline, such as Operating System Protection Profile (OSPP), Payment Card Industry Data Security Standard (PCI-DSS), and Health Insurance Portability and Accountability Act (HIPAA).

Note

The oscap-podman command is available from RHEL 8.2. For RHEL 8.1 and 8.0, use the workaround described in the Using OpenSCAP for scanning containers in RHEL 8 Knowledgebase article.

Prerequisites

The openscap-utils and scap-security-guide packages are installed.

Procedure

Get the ID of a container or a container image, for example:

# podman images
REPOSITORY                            TAG      IMAGE ID       CREATED       SIZE
registry.access.redhat.com/ubi8/ubi   latest   096cae65a207   7 weeks ago   239 MB

Evaluate the compliance of the container image with the HIPAA profile and save scan results into the report.html HTML file
```
# oscap-podman 096cae65a207 xccdf eval --report report.html --profile hipaa /usr/share/xml/scap/ssg/content/ssg-rhel8-ds.xml
```
Replace 096cae65a207 with the ID of your container image and the hipaa value with ospp or pci-dss if you assess security compliance with the OSPP or PCI-DSS baseline. Note that the oscap-podman command requires root privileges.

Verification

Check the results in a browser of your choice, for example:
```
$ firefox report.html &
```

Note

The rules marked as notapplicable are rules that do not apply to containerized systems. These rules apply only to bare-metal and virtualized systems.

Additional resources

oscap-podman(8) and scap-security-guide(8) man pages.
file:///usr/share/doc/scap-security-guide/ directory.

8.12. Supported versions of the SCAP Security Guide in RHEL

Officially supported versions of the SCAP Security Guide are versions provided in the related minor release of RHEL or in the related batch update of RHEL.

Table 8.2. Supported versions of the SCAP Security Guide in RHEL

Red Hat Enterprise Linux version	SCAP Security Guide version
RHEL 6.6	scap-security-guide-0.1.18-3.el6
RHEL 6.9	scap-security-guide-0.1.28-3.el6
RHEL 6.10	scap-security-guide-0.1.28-4.el6
RHEL 7.2 AUS	scap-security-guide-0.1.25-3.el7
RHEL 7.3 AUS	scap-security-guide-0.1.30-5.el7_3
RHEL 7.4 AUS, E4S	scap-security-guide-0.1.33-6.el7_4
RHEL 7.5 (batch update)	scap-security-guide-0.1.36-10.el7_5
RHEL 7.6 EUS	scap-security-guide-0.1.40-13.el7_6
RHEL 7.7 EUS	scap-security-guide-0.1.43-13.el7
RHEL 7.8 (batch update)	scap-security-guide-0.1.46-11.el7
RHEL 7.9 (batch update)	scap-security-guide-0.1.54-7.el7_9
RHEL 8.0 SAP	scap-security-guide-0.1.42-11.el8
RHEL 8.1 EUS	scap-security-guide-0.1.47-8.el8_1
RHEL 8.2 (batch update)	scap-security-guide-0.1.48-10.el8_2
RHEL 8.3	scap-security-guide-0.1.50-16.el8_3
RHEL 8.4	scap-security-guide-0.1.54-5.el8

8.13. SCAP Security Guide profiles supported in RHEL 8

Use only the SCAP content provided in the particular minor release of RHEL. This is because components that participate in hardening are sometimes updated with new capabilities. SCAP content changes to reflect these updates, but it is not always backward compatible.

In the following tables, you can find the profiles provided in each minor version of RHEL, together with the version of the policy with which the profile aligns.

Table 8.3. SCAP Security Guide profiles supported in RHEL 8.4

Profile name	Profile ID	Policy version
French National Agency for the Security of Information Systems (ANSSI) BP-028 Enhanced Level	`xccdf_org.ssgproject.content_profile_anssi_bp28_enhanced`	1.2
French National Agency for the Security of Information Systems (ANSSI) BP-028 Intermediary Level	`xccdf_org.ssgproject.content_profile_anssi_bp28_intermediary`	1.2
French National Agency for the Security of Information Systems (ANSSI) BP-028 Minimal Level	`xccdf_org.ssgproject.content_profile_anssi_bp28_minimal`	1.2
CIS Red Hat Enterprise Linux 8 Benchmark	`xccdf_org.ssgproject.content_profile_cis`	1.0.0
Unclassified Information in Non-federal Information Systems and Organizations (NIST 800-171)	`xccdf_org.ssgproject.content_profile_cui`	r1
Australian Cyber Security Centre (ACSC) Essential Eight	`xccdf_org.ssgproject.content_profile_e8`	not versioned
Health Insurance Portability and Accountability Act (HIPAA)	`xccdf_org.ssgproject.content_profile_hipaa`	not versioned
Protection Profile for General Purpose Operating Systems	`xccdf_org.ssgproject.content_profile_ospp`	4.2.1
PCI-DSS v3.2.1 Control Baseline for Red Hat Enterprise Linux 8	`xccdf_org.ssgproject.content_profile_pci-dss`	3.2.1
The Defense Information Systems Agency Security Technical Implementation Guide (DISA STIG) for Red Hat Enterprise Linux 8	`xccdf_org.ssgproject.content_profile_stig`	V1R1

Table 8.4. SCAP Security Guide profiles supported in RHEL 8.3

Profile name	Profile ID	Policy version
CIS Red Hat Enterprise Linux 8 Benchmark	`xccdf_org.ssgproject.content_profile_cis`	1.0.0
Unclassified Information in Non-federal Information Systems and Organizations (NIST 800-171)	`xccdf_org.ssgproject.content_profile_cui`	r1
Australian Cyber Security Centre (ACSC) Essential Eight	`xccdf_org.ssgproject.content_profile_e8`	not versioned
Health Insurance Portability and Accountability Act (HIPAA)	`xccdf_org.ssgproject.content_profile_hipaa`	not versioned
Protection Profile for General Purpose Operating Systems	`xccdf_org.ssgproject.content_profile_ospp`	4.2.1
PCI-DSS v3.2.1 Control Baseline for Red Hat Enterprise Linux 8	`xccdf_org.ssgproject.content_profile_pci-dss`	3.2.1
[DRAFT] The Defense Information Systems Agency Security Technical Implementation Guide (DISA STIG) for Red Hat Enterprise Linux 8	`xccdf_org.ssgproject.content_profile_stig`	draft

Table 8.5. SCAP Security Guide profiles supported in RHEL 8.2

Profile name	Profile ID	Policy version
Australian Cyber Security Centre (ACSC) Essential Eight	`xccdf_org.ssgproject.content_profile_e8`	not versioned
Protection Profile for General Purpose Operating Systems	`xccdf_org.ssgproject.content_profile_ospp`	4.2.1
PCI-DSS v3.2.1 Control Baseline for Red Hat Enterprise Linux 8	`xccdf_org.ssgproject.content_profile_pci-dss`	3.2.1
[DRAFT] DISA STIG for Red Hat Enterprise Linux 8	`xccdf_org.ssgproject.content_profile_stig`	draft

Table 8.6. SCAP Security Guide profiles supported in RHEL 8.1

Profile name	Profile ID	Policy version
Protection Profile for General Purpose Operating Systems	`xccdf_org.ssgproject.content_profile_ospp`	4.2.1
PCI-DSS v3.2.1 Control Baseline for Red Hat Enterprise Linux 8	`xccdf_org.ssgproject.content_profile_pci-dss`	3.2.1

Table 8.7. SCAP Security Guide profiles supported in RHEL 8.0

Profile name	Profile ID	Policy version
OSPP - Protection Profile for General Purpose Operating Systems	`xccdf_org.ssgproject.content_profile_ospp`	draft
PCI-DSS v3.2.1 Control Baseline for Red Hat Enterprise Linux 8	`xccdf_org.ssgproject.content_profile_pci-dss`	3.2.1

Additional Resources

For information about profiles in RHEL 7, see SCAP Security Guide profiles supported in RHEL 7

Chapter 9. Checking integrity with AIDE

Advanced Intrusion Detection Environment (AIDE) is a utility that creates a database of files on the system, and then uses that database to ensure file integrity and detect system intrusions.

9.1. Installing AIDE

The following steps are necessary to install AIDE and to initiate its database.

Prerequisites

The AppStream repository is enabled.

Procedure

To install the aide package:
```
# yum install aide
```
To generate an initial database:
```
# aide --init
```
Note
In the default configuration, the aide --init command checks just a set of directories and files defined in the /etc/aide.conf file. To include additional directories or files in the AIDE database, and to change their watched parameters, edit /etc/aide.conf accordingly.
To start using the database, remove the .new substring from the initial database file name:
```
# mv /var/lib/aide/aide.db.new.gz /var/lib/aide/aide.db.gz
```
To change the location of the AIDE database, edit the /etc/aide.conf file and modify the DBDIR value. For additional security, store the database, configuration, and the /usr/sbin/aide binary file in a secure location such as a read-only media.

9.2. Performing integrity checks with `AIDE`

Prerequisites

AIDE is properly installed and its database is initialized. See Installing AIDE

Procedure

To initiate a manual check:

# aide --check
Start timestamp: 2018-07-11 12:41:20 +0200 (AIDE 0.16)
AIDE found differences between database and filesystem!!
...
[trimmed for clarity]

At a minimum, configure the system to run AIDE weekly. Optimally, run AIDE daily. For example, to schedule a daily execution of AIDE at 04:05 a.m. using the cron command, add the following line to the /etc/crontab file:
```
 05 4 * * * root /usr/sbin/aide --check
```

9.3. Updating an AIDE database

After verifying the changes of your system such as, package updates or configuration files adjustments, Red Hat recommends updating your baseline AIDE database.

Prerequisites

AIDE is properly installed and its database is initialized. See Installing AIDE

Procedure

Update your baseline AIDE database:
```
# aide --update
```
The aide --update command creates the /var/lib/aide/aide.db.new.gz database file.
To start using the updated database for integrity checks, remove the .new substring from the file name.

Chapter 10. Encrypting block devices using LUKS

Disk encryption protects the data on a block device by encrypting it. To access the device’s decrypted contents, a user must provide a passphrase or key as authentication. This is particularly important when it comes to mobile computers and removable media: it helps to protect the device’s contents even if it has been physically removed from the system. The LUKS format is a default implementation of block device encryption in RHEL.

10.1. LUKS disk encryption

The Linux Unified Key Setup-on-disk-format (LUKS) enables you to encrypt block devices and it provides a set of tools that simplifies managing the encrypted devices. LUKS allows multiple user keys to decrypt a master key, which is used for the bulk encryption of the partition.

RHEL utilizes LUKS to perform block device encryption. By default, the option to encrypt the block device is unchecked during the installation. If you select the option to encrypt your disk, the system prompts you for a passphrase every time you boot the computer. This passphrase “unlocks” the bulk encryption key that decrypts your partition. If you choose to modify the default partition table, you can choose which partitions you want to encrypt. This is set in the partition table settings.

What LUKS does

LUKS encrypts entire block devices and is therefore well-suited for protecting contents of mobile devices such as removable storage media or laptop disk drives.
The underlying contents of the encrypted block device are arbitrary, which makes it useful for encrypting swap devices. This can also be useful with certain databases that use specially formatted block devices for data storage.
LUKS uses the existing device mapper kernel subsystem.
LUKS provides passphrase strengthening, which protects against dictionary attacks.
LUKS devices contain multiple key slots, allowing users to add backup keys or passphrases.

What LUKS does not do

Disk-encryption solutions like LUKS protect the data only when your system is off. Once the system is on and LUKS has decrypted the disk, the files on that disk are available to anyone who would normally have access to them.
LUKS is not well-suited for scenarios that require many users to have distinct access keys to the same device. The LUKS1 format provides eight key slots, LUKS2 up to 32 key slots.
LUKS is not well-suited for applications requiring file-level encryption.

Ciphers

The default cipher used for LUKS is aes-xts-plain64. The default key size for LUKS is 512 bits. The default key size for LUKS with Anaconda (XTS mode) is 512 bits. Ciphers that are available are:

AES - Advanced Encryption Standard
Twofish (a 128-bit block cipher)
Serpent

Additional resources

10.2. LUKS versions in RHEL 8

In RHEL 8, the default format for LUKS encryption is LUKS2. The legacy LUKS1 format remains fully supported and it is provided as a format compatible with earlier RHEL releases.

The LUKS2 format is designed to enable future updates of various parts without a need to modify binary structures. LUKS2 internally uses JSON text format for metadata, provides redundancy of metadata, detects metadata corruption and allows automatic repairs from a metadata copy.

Important

Do not use LUKS2 in systems that must be compatible with legacy systems that support only LUKS1. Note that RHEL 7 supports the LUKS2 format since version 7.6.

Warning

LUKS2 and LUKS1 use different commands to encrypt the disk. Using the wrong command for a LUKS version might cause data loss.

LUKS version	Encryption command
LUKS2	`cryptsetup reencrypt`
LUKS1	`cryptsetup-reencrypt`

Online re-encryption

The LUKS2 format supports re-encrypting encrypted devices while the devices are in use. For example, you do not have to unmount the file system on the device to perform the following tasks:

Change the volume key
Change the encryption algorithm

When encrypting a non-encrypted device, you must still unmount the file system. You can remount the file system after a short initialization of the encryption.

The LUKS1 format does not support online re-encryption.

Conversion

The LUKS2 format is inspired by LUKS1. In certain situations, you can convert LUKS1 to LUKS2. The conversion is not possible specifically in the following scenarios:

A LUKS1 device is marked as being used by a Policy-Based Decryption (PBD - Clevis) solution. The cryptsetup tool refuses to convert the device when some luksmeta metadata are detected.
A device is active. The device must be in the inactive state before any conversion is possible.

10.3. Options for data protection during LUKS2 re-encryption

LUKS2 provides several options that prioritize performance or data protection during the re-encryption process:

checksum

This is the default mode. It balances data protection and performance.

This mode stores individual checksums of the sectors in the re-encryption area, so the recovery process can detect which sectors LUKS2 already re-encrypted. The mode requires that the block device sector write is atomic.

journal

That is the safest mode but also the slowest. This mode journals the re-encryption area in the binary area, so LUKS2 writes the data twice.

none

This mode prioritizes performance and provides no data protection. It protects the data only against safe process termination, such as the SIGTERM signal or the user pressing Ctrl+C. Any unexpected system crash or application crash might result in data corruption.

You can select the mode using the --resilience option of cryptsetup.

If a LUKS2 re-encryption process terminates unexpectedly by force, LUKS2 can perform the recovery in one of the following ways:

Automatically, during the next LUKS2 device open action. This action is triggered either by the cryptsetup open command or by attaching the device with systemd-cryptsetup.
Manually, by using the cryptsetup repair command on the LUKS2 device.

10.4. Encrypting existing data on a block device using LUKS2

This procedure encrypts existing data on a not yet encrypted device using the LUKS2 format. A new LUKS header is stored in the head of the device.

Prerequisites

The block device contains a file system.
You have backed up your data.
Warning
You might lose your data during the encryption process: due to a hardware, kernel, or human failure. Ensure that you have a reliable backup before you start encrypting the data.

Procedure

Unmount all file systems on the device that you plan to encrypt. For example:
```
# umount /dev/sdb1
```
Make free space for storing a LUKS header. Choose one of the following options that suits your scenario:
- In the case of encrypting a logical volume, you can extend the logical volume without resizing the file system. For example:
```
# lvextend -L+32M vg00/lv00
```
- Extend the partition using partition management tools, such as parted.
- Shrink the file system on the device. You can use the resize2fs utility for the ext2, ext3, or ext4 file systems. Note that you cannot shrink the XFS file system.
Initialize the encryption. For example:
```
# cryptsetup reencrypt \ --encrypt \ --init-only \ --reduce-device-size 32M \ /dev/sdb1 sdb1_encrypted
```
The command asks you for a passphrase and starts the encryption process.

Mount the device:

# mount /dev/mapper/sdb1_encrypted /mnt/sdb1_encrypted

Start the online encryption:

# cryptsetup reencrypt --resume-only /dev/sdb1

Additional resources

cryptsetup(8), lvextend(8), resize2fs(8), and parted(8) man pages

10.5. Encrypting existing data on a block device using LUKS2 with a detached header

This procedure encrypts existing data on a block device without creating free space for storing a LUKS header. The header is stored in a detached location, which also serves as an additional layer of security. The procedure uses the LUKS2 encryption format.

Prerequisites

The block device contains a file system.
You have backed up your data.
Warning
You might lose your data during the encryption process: due to a hardware, kernel, or human failure. Ensure that you have a reliable backup before you start encrypting the data.

Procedure

Unmount all file systems on the device. For example:
```
# umount /dev/sdb1
```
Initialize the encryption:
```
# cryptsetup reencrypt \ --encrypt \ --init-only \ --header /path/to/header \ /dev/sdb1 sdb1_encrypted
```
Replace /path/to/header with a path to the file with a detached LUKS header. The detached LUKS header has to be accessible so that the encrypted device can be unlocked later.
The command asks you for a passphrase and starts the encryption process.

Mount the device:

# mount /dev/mapper/sdb1_encrypted /mnt/sdb1_encrypted

Start the online encryption:

# cryptsetup reencrypt --resume-only --header /path/to/header /dev/sdb1

Additional resources

cryptsetup(8) man page

10.6. Encrypting a blank block device using LUKS2

This procedure provides information about encrypting a blank block device using the LUKS2 format.

Prerequisites

A blank block device.

Procedure

Setup a partition as an encrypted LUKS partition:
```
# cryptsetup luksFormat /dev/sdb1
```
Open an encrypted LUKS partition:
```
# cryptsetup open /dev/sdb1 sdb1_encrypted
```
This unlocks the partition and maps it to a new device using the device mapper. This alerts kernel that device is an encrypted device and should be addressed through LUKS using the /dev/mapper/device_mapped_name so as not to overwrite the encrypted data.
To write encrypted data to the partition, it must be accessed through the device mapped name. To do this, you must create a file system. For example:
```
# mkfs -t ext4 /dev/mapper/sdb1_encrypted
```

Mount the device:

# mount /dev/mapper/sdb1_encrypted mount-point

Additional resources

cryptsetup(8) man page

10.7. Creating a LUKS encrypted volume using the storage role

You can use the storage role to create and configure a volume encrypted with LUKS by running an Ansible playbook.

Prerequisites

You have Red Hat Ansible Engine installed on the system from which you want to run the playbook.
Note
You do not have to have Red Hat Ansible Automation Platform installed on the systems on which you want to create the volume.
You have the rhel-system-roles package installed on the Ansible controller.
You have an inventory file detailing the systems on which you want to deploy a LUKS encrypted volume using the storage System Role.

Procedure

Create a new playbook.yml file with the following content:

- hosts: all
  vars:
    storage_volumes:
      - name: barefs
        type: disk
        disks:
         - sdb
        fs_type: xfs
        fs_label: label-name
        mount_point: /mnt/data
        encryption: true
        encryption_password: your-password
  roles:
   - rhel-system-roles.storage

Optional: Verify playbook syntax:

# ansible-playbook --syntax-check playbook.yml

Run the playbook on your inventory file:

# ansible-playbook -i inventory.file /path/to/file/playbook.yml

Additional resources

Encrypting block devices using LUKS
/usr/share/ansible/roles/rhel-system-roles.storage/README.md file

Chapter 11. Configuring automated unlocking of encrypted volumes using policy-based decryption

The Policy-Based Decryption (PBD) is a collection of technologies that enable unlocking encrypted root and secondary volumes of hard drives on physical and virtual machines. PBD uses a variety of unlocking methods, such as user passwords, a Trusted Platform Module (TPM) device, a PKCS #11 device connected to a system, for example, a smart card, or a special network server.

PBD allows combining different unlocking methods into a policy, which makes it possible to unlock the same volume in different ways. The current implementation of the PBD in Red Hat Enterprise Linux consists of the Clevis framework and plug-ins called pins. Each pin provides a separate unlocking capability. Currently, the following pins are available:

tang - allows volumes to be unlocked using a network server
tpm2 - allows volumes to be unlocked using a TPM2 policy

The Network Bound Disc Encryption (NBDE) is a subcategory of PBD that allows binding encrypted volumes to a special network server. The current implementation of the NBDE includes a Clevis pin for the Tang server and the Tang server itself.

11.1. Network-bound disk encryption

In Red Hat Enterprise Linux, NBDE is implemented through the following components and technologies:

Figure 11.1. NBDE scheme when using a LUKS1-encrypted volume. The luksmeta package is not used for LUKS2 volumes.

RHEL Security Guide 453350 0717 ECE NBDE

Tang is a server for binding data to network presence. It makes a system containing your data available when the system is bound to a certain secure network. Tang is stateless and does not require TLS or authentication. Unlike escrow-based solutions, where the server stores all encryption keys and has knowledge of every key ever used, Tang never interacts with any client keys, so it never gains any identifying information from the client.

Clevis is a pluggable framework for automated decryption. In NBDE, Clevis provides automated unlocking of LUKS volumes. The clevis package provides the client side of the feature.

A Clevis pin is a plug-in into the Clevis framework. One of such pins is a plug-in that implements interactions with the NBDE server — Tang.

Clevis and Tang are generic client and server components that provide network-bound encryption. In Red Hat Enterprise Linux, they are used in conjunction with LUKS to encrypt and decrypt root and non-root storage volumes to accomplish Network-Bound Disk Encryption.

Both client- and server-side components use the José library to perform encryption and decryption operations.

When you begin provisioning NBDE, the Clevis pin for Tang server gets a list of the Tang server’s advertised asymmetric keys. Alternatively, since the keys are asymmetric, a list of Tang’s public keys can be distributed out of band so that clients can operate without access to the Tang server. This mode is called offline provisioning.

The Clevis pin for Tang uses one of the public keys to generate a unique, cryptographically-strong encryption key. Once the data is encrypted using this key, the key is discarded. The Clevis client should store the state produced by this provisioning operation in a convenient location. This process of encrypting data is the provisioning step.

The LUKS version 2 (LUKS2) is the default format in Red Hat Enterprise Linux 8, hence, the provisioning state for NBDE is stored as a token in a LUKS2 header. The leveraging of provisioning state for NBDE by the luksmeta package is used only for volumes encrypted with LUKS1. The Clevis pin for Tang supports both LUKS1 and LUKS2 without specification need.

When the client is ready to access its data, it loads the metadata produced in the provisioning step and it responds to recover the encryption key. This process is the recovery step.

In NBDE, Clevis binds a LUKS volume using a pin so that it can be automatically unlocked. After successful completion of the binding process, the disk can be unlocked using the provided Dracut unlocker.

Note

If the kdump kernel crash dumping mechanism is set to save the content of the system memory to a LUKS-encrypted device, you are prompted for entering a password during the second kernel boot.

11.2. Installing an encryption client - Clevis

Use this procedure to deploy and start using the Clevis pluggable framework on your system.

Procedure

To install Clevis and its pins on a system with an encrypted volume:
```
# yum install clevis
```
To decrypt data, use a clevis decrypt command and provide a cipher text in the JSON Web Encryption (JWE) format, for example:
```
$ clevis decrypt < secret.jwe
```

Additional resources

clevis(1) man page

Built-in CLI help after entering the clevis command without any argument:

$ clevis
Usage: clevis COMMAND [OPTIONS]

clevis decrypt             Decrypts using the policy defined at encryption time
clevis encrypt sss         Encrypts using a Shamir's Secret Sharing policy
clevis encrypt tang        Encrypts using a Tang binding server policy
clevis encrypt tpm2        Encrypts using a TPM2.0 chip binding policy
clevis luks bind           Binds a LUKS device using the specified policy
clevis luks list           Lists pins bound to a LUKSv1 or LUKSv2 device
clevis luks pass           Returns the LUKS passphrase used for binding a particular slot.
clevis luks regen          Regenerate LUKS metadata
clevis luks report         Report any key rotation on the server side
clevis luks unbind         Unbinds a pin bound to a LUKS volume
clevis luks unlock         Unlocks a LUKS volume

11.3. Deploying a Tang server with SELinux in enforcing mode

Use this procedure to deploy a Tang server running on a custom port as a confined service in SELinux enforcing mode.

Prerequisites

The policycoreutils-python-utils package and its dependencies are installed.

Procedure

To install the tang package and its dependencies, enter the following command as root:
```
# yum install tang
```
Pick an unoccupied port, for example, 7500/tcp, and allow the tangd service to bind to that port:
```
# semanage port -a -t tangd_port_t -p tcp 7500
```
Note that a port can be used only by one service at a time, and thus an attempt to use an already occupied port implies the ValueError: Port already defined error message.

Open the port in the firewall:

# firewall-cmd --add-port=7500/tcp
# firewall-cmd --runtime-to-permanent

Enable the tangd service:
```
# systemctl enable tangd.socket
```
Create an override file:
```
# systemctl edit tangd.socket
```
In the following editor screen, which opens an empty override.conf file located in the /etc/systemd/system/tangd.socket.d/ directory, change the default port for the Tang server from 80 to the previously picked number by adding the following lines:
```
[Socket]
ListenStream=
ListenStream=7500
```
Save the file and exit the editor.
Reload the changed configuration:
```
# systemctl daemon-reload
```

Check that your configuration is working:

# systemctl show tangd.socket -p Listen
Listen=[::]:7500 (Stream)

Start the tangd service:
```
# systemctl start tangd.socket
```
Because tangd uses the systemd socket activation mechanism, the server starts as soon as the first connection comes in. A new set of cryptographic keys is automatically generated at the first start. To perform cryptographic operations such as manual key generation, use the jose utility.

Additional resources

tang(8), semanage(8), firewall-cmd(1), jose(1), systemd.unit(5), and systemd.socket(5) man pages

11.4. Rotating Tang server keys and updating bindings on clients

Use the following steps to rotate your Tang server keys and update existing bindings on clients. The precise interval at which you should rotate them depends on your application, key sizes, and institutional policy.

Alternatively, you can rotate Tang keys by using the nbde_server RHEL system role. See Using the nbde_server system role for setting up multiple Tang servers for more information.

Prerequisites

A Tang server is running.
The clevis and clevis-luks packages are installed on your clients.
Note that clevis luks list, clevis luks report, and clevis luks regen have been introduced in RHEL 8.2.

Procedure

Rename all keys in the /var/db/tang key database directory to have a leading . to hide them from advertisement. Note that the file names in the following example differs from unique file names in the key database directory of your Tang server:

# cd /var/db/tang
# ls -l
-rw-r--r--. 1 root root 349 Feb  7 14:55 UV6dqXSwe1bRKG3KbJmdiR020hY.jwk
-rw-r--r--. 1 root root 354 Feb  7 14:55 y9hxLTQSiSB5jSEGWnjhY8fDTJU.jwk
# mv UV6dqXSwe1bRKG3KbJmdiR020hY.jwk .UV6dqXSwe1bRKG3KbJmdiR020hY.jwk
# mv y9hxLTQSiSB5jSEGWnjhY8fDTJU.jwk .y9hxLTQSiSB5jSEGWnjhY8fDTJU.jwk

Check that you renamed and therefore hid all keys from the Tang server advertisement:
```
# ls -l
total 0
```

Generate new keys using the /usr/libexec/tangd-keygen command in /var/db/tang on the Tang server:

# /usr/libexec/tangd-keygen /var/db/tang
# ls /var/db/tang
3ZWS6-cDrCG61UPJS2BMmPU4I54.jwk zyLuX6hijUy_PSeUEFDi7hi38.jwk

Check that your Tang server advertises the signing key from the new key pair, for example:
```
# tang-show-keys 7500
3ZWS6-cDrCG61UPJS2BMmPU4I54
```

On your NBDE clients, use the clevis luks report command to check if the keys advertised by the Tang server remains the same. You can identify slots with the relevant binding using the clevis luks list command, for example:

# clevis luks list -d /dev/sda2
1: tang '{"url":"http://tang.srv"}'
# clevis luks report -d /dev/sda2 -s 1
...
Report detected that some keys were rotated.
Do you want to regenerate luks metadata with "clevis luks regen -d /dev/sda2 -s 1"? [ynYN]

To regenerate LUKS metadata for the new keys either press y to the prompt of the previous command, or use the clevis luks regen command:
```
# clevis luks regen -d /dev/sda2 -s 1
```
When you are sure that all old clients use the new keys, you can remove the old keys from the Tang server, for example:
```
# cd /var/db/tang
# rm .*.jwk
```

Warning

Removing the old keys while clients are still using them can result in data loss. If you accidentally remove such keys, use the clevis luks regen command on the clients, and provide your LUKS password manually.

Additional resources

tang-show-keys(1), clevis-luks-list(1), clevis-luks-report(1), and clevis-luks-regen(1) man pages

11.5. Configuring automated unlocking using a Tang key in the web console

Configure automated unlocking of a LUKS-encrypted storage device using a key provided by a Tang server.

Prerequisites

The RHEL 8 web console has been installed.
For details, see Installing the web console.
The cockpit-storaged package is installed on your system.
The cockpit.socket service is running at port 9090.
The clevis, tang, and clevis-dracut packages are installed.
A Tang server is running.

Procedure

Open the RHEL web console by entering the following address in a web browser:
```
https://localhost:9090
```
Replace the localhost part by the remote server’s host name or IP address when you connect to a remote system.
Provide your credentials and click Storage. Select an encrypted device and click Encryption in the Content part:
Click + in the Keys section to add a Tang key:
Provide the address of your Tang server and a password that unlocks the LUKS-encrypted device. Click Add to confirm:
The following dialog window provides a command to verify that the key hash matches. RHEL 8.2 introduced the tang-show-keys script, and you can obtain the key hash using the following command on the Tang server running on the port 7500:
```
# tang-show-keys 7500
3ZWS6-cDrCG61UPJS2BMmPU4I54
```
On RHEL 8.1 and earlier, obtain the key hash using the following command:
```
# curl -s localhost:7500/adv | jose fmt -j- -g payload -y -o- | jose jwk use -i- -r -u verify -o- | jose jwk thp -i-
3ZWS6-cDrCG61UPJS2BMmPU4I54
```
Click Trust key when the key hashes in the web console and in the output of previously listed commands are the same:
To enable the early boot system to process the disk binding, click Terminal at the bottom of the left navigation bar and enter the following commands:
```
# yum install clevis-dracut
# dracut -fv --regenerate-all
```

Verification

Check that the newly added Tang key is now listed in the Keys section with the Keyserver type:

Verify that the bindings are available for the early boot, for example:

# lsinitrd | grep clevis
clevis
clevis-pin-sss
clevis-pin-tang
clevis-pin-tpm2
-rwxr-xr-x   1 root     root         1600 Feb 11 16:30 usr/bin/clevis
-rwxr-xr-x   1 root     root         1654 Feb 11 16:30 usr/bin/clevis-decrypt
...
-rwxr-xr-x   2 root     root           45 Feb 11 16:30 usr/lib/dracut/hooks/initqueue/settled/60-clevis-hook.sh
-rwxr-xr-x   1 root     root         2257 Feb 11 16:30 usr/libexec/clevis-luks-askpass

Additional resources

Getting started using the RHEL web console

11.6. Deploying an encryption client for an NBDE system with Tang

The following procedure contains steps to configure automated unlocking of an encrypted volume with a Tang network server.

Prerequisites

The Clevis framework is installed.
A Tang server is available.

Procedure

To bind a Clevis encryption client to a Tang server, use the clevis encrypt tang sub-command:
```
$ clevis encrypt tang '{"url":"http://tang.srv:port"}' < input-plain.txt > secret.jwe
The advertisement contains the following signing keys:

_OsIk0T-E2l6qjfdDiwVmidoZjA

Do you wish to trust these keys? [ynYN] y
```
Change the http://tang.srv:port URL in the previous example to match the URL of the server where tang is installed. The secret.jwe output file contains your encrypted cipher text in the JSON Web Encryption format. This cipher text is read from the input-plain.txt input file.
Alternatively, if your configuration requires a non-interactive communication with a Tang server without SSH access, you can download an advertisement and save it to a file:
```
$ curl -sfg http://tang.srv:port/adv -o adv.jws
```
Use the advertisement in the adv.jws file for any following tasks, such as encryption of files or messages:
```
$ echo 'hello' | clevis encrypt tang '{"url":"http://tang.srv:port","adv":"adv.jws"}'
```
To decrypt data, use the clevis decrypt command and provide the cipher text (JWE):
```
$ clevis decrypt < secret.jwe > output-plain.txt
```

Additional resources

clevis-encrypt-tang(1), clevis-luks-unlockers(7), and clevis(1) man pages
clevis, clevis decrypt, and clevis encrypt tang commands without any arguments show the built-in CLI help, for example:
```
$ clevis encrypt tang
Usage: clevis encrypt tang CONFIG < PLAINTEXT > JWE
...
```

11.7. Removing a Clevis pin from a LUKS-encrypted volume manually

Use the following procedure for manual removing the metadata created by the clevis luks bind command and also for wiping a key slot that contains passphrase added by Clevis.

Important

The recommended way to remove a Clevis pin from a LUKS-encrypted volume is through the clevis luks unbind command. The removal procedure using clevis luks unbind consists of only one step and works for both LUKS1 and LUKS2 volumes. The following example command removes the metadata created by the binding step and wipe the key slot 1 on the /dev/sda2 device:

# clevis luks unbind -d /dev/sda2 -s 1

Prerequisites

A LUKS-encrypted volume with a Clevis binding.

Procedure

Check which LUKS version the volume, for example /dev/sda2, is encrypted by and identify a slot and a token that is bound to Clevis:

# cryptsetup luksDump /dev/sda2
LUKS header information
Version:        2
...
Keyslots:
  0: luks2
...
1: luks2
      Key:        512 bits
      Priority:   normal
      Cipher:     aes-xts-plain64
...
      Tokens:
        0: clevis
              Keyslot:  1
...

In the previous example, the Clevis token is identified by 0 and the associated key slot is 1.

In case of LUKS2 encryption, remove the token:

# cryptsetup token remove --token-id 0 /dev/sda2

If your device is encrypted by LUKS1, which is indicated by the Version: 1 string in the output of the cryptsetup luksDump command, perform this additional step with the luksmeta wipe command:
```
# luksmeta wipe -d /dev/sda2 -s 1
```
Wipe the key slot containing the Clevis passphrase:
```
# cryptsetup luksKillSlot /dev/sda2 1
```

Additional resources

clevis-luks-unbind(1), cryptsetup(8), and luksmeta(8) man pages

11.8. Deploying an encryption client with a TPM 2.0 policy

The following procedure contains steps to configure automated unlocking of an encrypted volume with a Trusted Platform Module 2.0 (TPM 2.0) policy.

Prerequisites

The Clevis framework is installed. See Installing an encryption client - Clevis
A system with the 64-bit Intel or 64-bit AMD architecture

Procedure

To deploy a client that encrypts using a TPM 2.0 chip, use the clevis encrypt tpm2 sub-command with the only argument in form of the JSON configuration object:
```
$ clevis encrypt tpm2 '{}' < input-plain.txt > secret.jwe
```
To choose a different hierarchy, hash, and key algorithms, specify configuration properties, for example:
```
$ clevis encrypt tpm2 '{"hash":"sha1","key":"rsa"}' < input-plain.txt > secret.jwe
```
To decrypt the data, provide the ciphertext in the JSON Web Encryption (JWE) format:
```
$ clevis decrypt < secret.jwe > output-plain.txt
```

The pin also supports sealing data to a Platform Configuration Registers (PCR) state. That way, the data can only be unsealed if the PCRs hashes values match the policy used when sealing.

For example, to seal the data to the PCR with index 0 and 1 for the SHA-1 bank:

$ clevis encrypt tpm2 '{"pcr_bank":"sha1","pcr_ids":"0,1"}' < input-plain.txt > secret.jwe

Additional resources

clevis-encrypt-tpm2(1) man page

11.9. Configuring manual enrollment of LUKS-encrypted volumes

Use the following steps to configure unlocking of LUKS-encrypted volumes with NBDE.

Prerequisites

A Tang server is running and available.

Procedure

To automatically unlock an existing LUKS-encrypted volume, install the clevis-luks subpackage:
```
# yum install clevis-luks
```

Identify the LUKS-encrypted volume for PBD. In the following example, the block device is referred as /dev/sda2:

# lsblk
NAME                                          MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda                                             8:0    0    12G  0 disk
├─sda1                                          8:1    0     1G  0 part  /boot
└─sda2                                          8:2    0    11G  0 part
  └─luks-40e20552-2ade-4954-9d56-565aa7994fb6 253:0    0    11G  0 crypt
    ├─rhel-root                               253:0    0   9.8G  0 lvm   /
    └─rhel-swap                               253:1    0   1.2G  0 lvm   [SWAP]

Bind the volume to a Tang server using the clevis luks bind command:

# clevis luks bind -d /dev/sda2 tang '{"url":"http://tang.srv"}'
The advertisement contains the following signing keys:

_OsIk0T-E2l6qjfdDiwVmidoZjA

Do you wish to trust these keys? [ynYN] y
You are about to initialize a LUKS device for metadata storage.
Attempting to initialize it may result in data loss if data was
already written into the LUKS header gap in a different format.
A backup is advised before initialization is performed.

Do you wish to initialize /dev/sda2? [yn] y
Enter existing LUKS password:

This command performs four steps:

Creates a new key with the same entropy as the LUKS master key.
Encrypts the new key with Clevis.
Stores the Clevis JWE object in the LUKS2 header token or uses LUKSMeta if the non-default LUKS1 header is used.
Enables the new key for use with LUKS.
Note
The binding procedure assumes that there is at least one free LUKS password slot. The clevis luks bind command takes one of the slots.

The volume can now be unlocked with your existing password as well as with the Clevis policy.
To enable the early boot system to process the disk binding, use the dracut tool on an already installed system:
```
# yum install clevis-dracut
```
In Red Hat Enterprise Linux 8, Clevis produces a generic initrd (initial ramdisk) without host-specific configuration options and does not automatically add parameters such as rd.neednet=1 to the kernel command line. If your configuration relies on a Tang pin that requires network during early boot, use the --hostonly-cmdline argument and dracut adds rd.neednet=1 when it detects a Tang binding:
```
# dracut -fv --regenerate-all --hostonly-cmdline
```
Alternatively, create a .conf file in the /etc/dracut.conf.d/, and add the hostonly_cmdline=yes option to the file, for example:
```
# echo "hostonly_cmdline=yes" > /etc/dracut.conf.d/clevis.conf
```
Then you can use dracut without --hostonly-cmdline:
```
# dracut -fv --regenerate-all
```

Verification

To verify that the Clevis JWE object is successfully placed in a LUKS header, use the clevis luks list command:
```
# clevis luks list -d /dev/sda2
1: tang '{"url":"http://tang.srv:port"}'
```

Important

To use NBDE for clients with static IP configuration (without DHCP), pass your network configuration to the dracut tool manually, for example:

# dracut -fv --regenerate-all --kernel-cmdline "ip=192.0.2.10::192.0.2.1:255.255.255.0::ens3:none:192.0.2.45"

Alternatively, create a .conf file in the /etc/dracut.conf.d/ directory with the static network information. For example:

# cat /etc/dracut.conf.d/static_ip.conf
kernel_cmdline="ip=192.0.2.10::192.0.2.1:255.255.255.0::ens3:none:192.0.2.45"

Regenerate the initial RAM disk image:

# dracut -fv --regenerate-all

Additional resources

clevis-luks-bind(1) and dracut.cmdline(7) man pages

11.10. Configuring automated enrollment of LUKS-encrypted volumes using Kickstart

Follow the steps in this procedure to configure an automated installation process that uses Clevis for enrollment of LUKS-encrypted volumes.

Procedure

Instruct Kickstart to partition the disk such that LUKS encryption has enabled for all mount points, other than /boot, with a temporary password. The password is temporary for this step of the enrollment process.

part /boot --fstype="xfs" --ondisk=vda --size=256
part / --fstype="xfs" --ondisk=vda --grow --encrypted --passphrase=temppass

Note that OSPP-complaint systems require a more complex configuration, for example:

part /boot --fstype="xfs" --ondisk=vda --size=256
part / --fstype="xfs" --ondisk=vda --size=2048 --encrypted --passphrase=temppass
part /var --fstype="xfs" --ondisk=vda --size=1024 --encrypted --passphrase=temppass
part /tmp --fstype="xfs" --ondisk=vda --size=1024 --encrypted --passphrase=temppass
part /home --fstype="xfs" --ondisk=vda --size=2048 --grow --encrypted --passphrase=temppass
part /var/log --fstype="xfs" --ondisk=vda --size=1024 --encrypted --passphrase=temppass
part /var/log/audit --fstype="xfs" --ondisk=vda --size=1024 --encrypted --passphrase=temppass

Install the related Clevis packages by listing them in the %packages section:
```
%packages
clevis-dracut
%end
```
Call clevis luks bind to perform binding in the %post section. Afterward, remove the temporary password:
```
%post
curl -sfg http://tang.srv/adv -o adv.jws
clevis luks bind -f -k- -d /dev/vda2 \
tang '{"url":"http://tang.srv","adv":"adv.jws"}' \ <<< "temppass"
cryptsetup luksRemoveKey /dev/vda2 <<< "temppass"
%end
```
In the previous example, note that we download the advertisement from the Tang server as part of our binding configuration, enabling binding to be completely non-interactive.
Warning
The cryptsetup luksRemoveKey command prevents any further administration of a LUKS2 device on which you apply it. You can recover a removed master key using the dmsetup command only for LUKS1 devices.

You can use an analogous procedure when using a TPM 2.0 policy instead of a Tang server.

Additional resources

clevis(1), clevis-luks-bind(1), cryptsetup(8), and dmsetup(8) man pages
Installing Red Hat Enterprise Linux 8 using Kickstart

11.11. Configuring automated unlocking of a LUKS-encrypted removable storage device

Use this procedure to set up an automated unlocking process of a LUKS-encrypted USB storage device.

Procedure

To automatically unlock a LUKS-encrypted removable storage device, such as a USB drive, install the clevis-udisks2 package:
```
# yum install clevis-udisks2
```
Reboot the system, and then perform the binding step using the clevis luks bind command as described in Configuring manual enrollment of LUKS-encrypted volumes, for example:
```
# clevis luks bind -d /dev/sdb1 tang '{"url":"http://tang.srv"}'
```
The LUKS-encrypted removable device can be now unlocked automatically in your GNOME desktop session. The device bound to a Clevis policy can be also unlocked by the clevis luks unlock command:
```
# clevis luks unlock -d /dev/sdb1
```

You can use an analogous procedure when using a TPM 2.0 policy instead of a Tang server.

Additional resources

clevis-luks-unlockers(7) man page

11.12. Deploying high-availability NBDE systems

Tang provides two methods for building a high-availability deployment:

Client redundancy (recommended): Clients should be configured with the ability to bind to multiple Tang servers. In this setup, each Tang server has its own keys and clients can decrypt by contacting a subset of these servers. Clevis already supports this workflow through its sss plug-in. Red Hat recommends this method for a high-availability deployment.
Key sharing: For redundancy purposes, more than one instance of Tang can be deployed. To set up a second or any subsequent instance, install the tang packages and copy the key directory to the new host using rsync over SSH. Note that Red Hat does not recommend this method because sharing keys increases the risk of key compromise and requires additional automation infrastructure.

11.12.1. High-available NBDE using Shamir’s Secret Sharing

Shamir’s Secret Sharing (SSS) is a cryptographic scheme that divides a secret into several unique parts. To reconstruct the secret, a number of parts is required. The number is called threshold and SSS is also referred to as a thresholding scheme.

Clevis provides an implementation of SSS. It creates a key and divides it into a number of pieces. Each piece is encrypted using another pin including even SSS recursively. Additionally, you define the threshold t. If an NBDE deployment decrypts at least t pieces, then it recovers the encryption key and the decryption process succeeds. When Clevis detects a smaller number of parts than specified in the threshold, it prints an error message.

11.12.1.1. Example 1: Redundancy with two Tang servers

The following command decrypts a LUKS-encrypted device when at least one of two Tang servers is available:

# clevis luks bind -d /dev/sda1 sss '{"t":1,"pins":{"tang":[{"url":"http://tang1.srv"},{"url":"http://tang2.srv"}]}}'

The previous command used the following configuration scheme:

{
    "t":1,
    "pins":{
        "tang":[
            {
                "url":"http://tang1.srv"
            },
            {
                "url":"http://tang2.srv"
            }
        ]
    }
}

In this configuration, the SSS threshold t is set to 1 and the clevis luks bind command successfully reconstructs the secret if at least one from two listed tang servers is available.

11.12.1.2. Example 2: Shared secret on a Tang server and a TPM device

The following command successfully decrypts a LUKS-encrypted device when both the tang server and the tpm2 device are available:

# clevis luks bind -d /dev/sda1 sss '{"t":2,"pins":{"tang":[{"url":"http://tang1.srv"}], "tpm2": {"pcr_ids":"0,1"}}}'

The configuration scheme with the SSS threshold 't' set to '2' is now:

{
    "t":2,
    "pins":{
        "tang":[
            {
                "url":"http://tang1.srv"
            }
        ],
        "tpm2":{
            "pcr_ids":"0,1"
        }
    }
}

Additional resources

tang(8) (section High Availability), clevis(1) (section Shamir’s Secret Sharing), and clevis-encrypt-sss(1) man pages

11.13. Deployment of virtual machines in a NBDE network

The clevis luks bind command does not change the LUKS master key. This implies that if you create a LUKS-encrypted image for use in a virtual machine or cloud environment, all the instances that run this image will share a master key. This is extremely insecure and should be avoided at all times.

This is not a limitation of Clevis but a design principle of LUKS. If you wish to have encrypted root volumes in a cloud, you need to make sure that you perform the installation process (usually using Kickstart) for each instance of Red Hat Enterprise Linux in a cloud as well. The images cannot be shared without also sharing a LUKS master key.

If you intend to deploy automated unlocking in a virtualized environment, Red Hat strongly recommends that you use systems such as lorax or virt-install together with a Kickstart file (see Configuring automated enrollment of LUKS-encrypted volumes using Kickstart) or another automated provisioning tool to ensure that each encrypted VM has a unique master key.

Note

Automated unlocking with a TPM 2.0 policy is not supported in a virtual machine.

Additional resources

clevis-luks-bind(1) man page

11.14. Building automatically-enrollable VM images for cloud environments using NBDE

Deploying automatically-enrollable encrypted images in a cloud environment can provide a unique set of challenges. Like other virtualization environments, it is recommended to reduce the number of instances started from a single image to avoid sharing the LUKS master key.

Therefore, the best practice is to create customized images that are not shared in any public repository and that provide a base for the deployment of a limited amount of instances. The exact number of instances to create should be defined by deployment’s security policies and based on the risk tolerance associated with the LUKS master key attack vector.

To build LUKS-enabled automated deployments, systems such as Lorax or virt-install together with a Kickstart file should be used to ensure master key uniqueness during the image building process.

Cloud environments enable two Tang server deployment options which we consider here. First, the Tang server can be deployed within the cloud environment itself. Second, the Tang server can be deployed outside of the cloud on independent infrastructure with a VPN link between the two infrastructures.

Deploying Tang natively in the cloud does allow for easy deployment. However, given that it shares infrastructure with the data persistence layer of ciphertext of other systems, it may be possible for both the Tang server’s private key and the Clevis metadata to be stored on the same physical disk. Access to this physical disk permits a full compromise of the ciphertext data.

Important

For this reason, Red Hat strongly recommends maintaining a physical separation between the location where the data is stored and the system where Tang is running. This separation between the cloud and the Tang server ensures that the Tang server’s private key cannot be accidentally combined with the Clevis metadata. It also provides local control of the Tang server if the cloud infrastructure is at risk.

11.15. Deploying Tang as a container

The rhel8-tang container image provides Tang-server decryption capabilities for Clevis clients that run either in OpenShift Container Platform (OCP) clusters or in separate virtual machines.

Prerequisites

The podman package and its dependencies are installed on the system.
You have logged in on the registry.redhat.io container catalog using the podman login registry.redhat.io command. See Red Hat Container Registry Authentication for more information.
The Clevis client is installed on systems containing LUKS-encrypted volumes that you want to automatically unlock by using a Tang server.

Procedure

Pull the rhel8-tang container image from the registry.redhat.io registry:
```
# podman pull registry.redhat.io/rhel8/rhel8-tang
```
Run the container, specify its port, and specify the path to the Tang keys. The previous example runs the rhel8-tang container, specifies the port 7500, and indicates a path to the Tang keys of the /var/db/tang directory:
```
# podman run -d -p 7500:_7500_ -v tang-keys:/var/db/tang --name tang registry.redhat.io/rhel8/rhel8-tang
```
Note that Tang uses port 80 by default but this may collide with other services such as the Apache HTTP server.

[Optional] For increased security, rotate the Tang keys periodically. You can use the tangd-rotate-keys script, for example:

# podman run --rm -v tang-keys:/var/db/tang registry.redhat.io/rhel8/rhel8-tang tangd-rotate-keys -v -d /var/db/tang
Rotated key 'rZAMKAseaXBe0rcKXL1hCCIq-DY.jwk' -> .'rZAMKAseaXBe0rcKXL1hCCIq-DY.jwk'
Rotated key 'x1AIpc6WmnCU-CabD8_4q18vDuw.jwk' -> .'x1AIpc6WmnCU-CabD8_4q18vDuw.jwk'
Created new key GrMMX_WfdqomIU_4RyjpcdlXb0E.jwk
Created new key _dTTfn17sZZqVAp80u3ygFDHtjk.jwk
Keys rotated successfully.

Verification

On a system that contains LUKS-encrypted volumes for automated unlocking by the presence of the Tang server, check that the Clevis client can encrypt and decrypt a plain-text message using Tang:
```
# echo test | clevis encrypt tang '{"url":"http://localhost:_7500_"}' | clevis decrypt
The advertisement contains the following signing keys:

x1AIpc6WmnCU-CabD8_4q18vDuw

Do you wish to trust these keys? [ynYN] y
test
```
The previous example command shows the test string at the end of its output when a Tang server is available on the localhost URL and communicates through port 7500.

Additional resources

podman(1), clevis(1), and tang(8) man pages

11.16. Introduction to the Clevis and Tang system roles

RHEL System Roles is a collection of Ansible roles and modules that provide a consistent configuration interface to remotely manage multiple RHEL systems.

RHEL 8.3 introduced Ansible roles for automated deployments of Policy-Based Decryption (PBD) solutions using Clevis and Tang. The rhel-system-roles package contains these system roles, the related examples, and also the reference documentation.

The nbde_client system role enables you to deploy multiple Clevis clients in an automated way. Note that the nbde_client role supports only Tang bindings, and you cannot use it for TPM2 bindings at the moment.

The nbde_client role requires volumes that are already encrypted using LUKS. This role supports to bind a LUKS-encrypted volume to one or more Network-Bound (NBDE) servers - Tang servers. You can either preserve the existing volume encryption with a passphrase or remove it. After removing the passphrase, you can unlock the volume only using NBDE. This is useful when a volume is initially encrypted using a temporary key or password that you should remove after the system you provision the system.

If you provide both a passphrase and a key file, the role uses what you have provided first. If it does not find any of these valid, it attempts to retrieve a passphrase from an existing binding.

PBD defines a binding as a mapping of a device to a slot. This means that you can have multiple bindings for the same device. The default slot is slot 1.

The nbde_client role provides also the state variable. Use the present value for either creating a new binding or updating an existing one. Contrary to a clevis luks bind command, you can use state: present also for overwriting an existing binding in its device slot. The absent value removes a specified binding.

Using the nbde_server role, you can deploy and manage a Tang server as part of an automated disk encryption solution. This role supports the following features:

Rotating Tang keys
Deploying and backing up Tang keys

Additional resources

For a detailed reference on Network-Bound Disk Encryption (NBDE) role variables, install the rhel-system-roles package, and see the README.md and README.html files in the /usr/share/doc/rhel-system-roles/nbde_client/ and /usr/share/doc/rhel-system-roles/nbde_server/ directories.
For example system-roles playbooks, install the rhel-system-roles package, and see the /usr/share/ansible/roles/rhel-system-roles.nbde_server/examples/ directories.
For more information on RHEL System Roles, see Introduction to RHEL System Roles

11.17. Using the nbde_server system role for setting up multiple Tang servers

Follow the steps to prepare and apply an Ansible playbook containing your Tang-server settings.

Prerequisites

Your Red Hat Ansible Engine subscription is attached to the system. See the How do I download and install Red Hat Ansible Engine article for more information.

Procedure

Enable the RHEL Ansible repository, for example:

# subscription-manager repos --enable ansible-2-for-rhel-8-x86_64-rpms

Install Ansible Engine:
```
# yum install ansible
```
Install RHEL system roles:
```
# yum install rhel-system-roles
```
Prepare your playbook containing settings for Tang servers. You can either start from the scratch, or use one of the example playbooks from the /usr/share/ansible/roles/rhel-system-roles.nbde_server/examples/ directory.
```
# cp /usr/share/ansible/roles/rhel-system-roles.nbde_server/examples/simple_deploy.yml ./my-tang-playbook.yml
```
Edit the playbook in a text editor of your choice, for example:
```
# vi my-tang-playbook.yml
```
Add the required parameters. The following example playbook ensures deploying of your Tang server and a key rotation:
```
---
- hosts: all

  vars:
    nbde_server_rotate_keys: yes

  roles:
    - linux-system-roles.nbde_server
```

Apply the finished playbook:

# ansible-playbook -i host1,host2,host3 my-tang-playbook.yml

Additional resources

For more information, install the rhel-system-roles package, and see the /usr/share/doc/rhel-system-roles/nbde_server/ and usr/share/ansible/roles/rhel-system-roles.nbde_server/ directories.

11.18. Using the nbde_client system role for setting up multiple Clevis clients

Follow the steps to prepare and apply an Ansible playbook containing your Clevis-client settings.

Note

The nbde_client system role supports only Tang bindings. This means that you cannot use it for TPM2 bindings at the moment.

Prerequisites

Your Red Hat Ansible Engine subscription is attached to the system. See the How do I download and install Red Hat Ansible Engine article for more information.
Your volumes are already encrypted by LUKS.

Procedure

Enable the RHEL Ansible repository, for example:

# subscription-manager repos --enable ansible-2-for-rhel-8-x86_64-rpms

Install Ansible Engine:
```
# yum install ansible
```
Install RHEL system roles:
```
# yum install rhel-system-roles
```
Prepare your playbook containing settings for Clevis clients. You can either start from the scratch, or use one of the example playbooks from the /usr/share/ansible/roles/rhel-system-roles.nbde_client/examples/ directory.
```
# cp /usr/share/ansible/roles/rhel-system-roles.nbde_client/examples/high_availability.yml ./my-clevis-playbook.yml
```
Edit the playbook in a text editor of your choice, for example:
```
# vi my-clevis-playbook.yml
```

Add the required parameters. The following example playbook configures Clevis clients for automated unlocking of two LUKS-encrypted volumes by when at least one of two Tang servers is available:

---
- hosts: all

  vars:
    nbde_client_bindings:
      - device: /dev/rhel/root
        encryption_key_src: /etc/luks/keyfile
        servers:
          - http://server1.example.com
          - http://server2.example.com
      - device: /dev/rhel/swap
        encryption_key_src: /etc/luks/keyfile
        servers:
          - http://server1.example.com
          - http://server2.example.com

  roles:
    - linux-system-roles.nbde_client

Apply the finished playbook:

# ansible-playbook -i host1,host2,host3 my-clevis-playbook.yml

Additional resources

For details about the parameters and additional information about the nbde_client role, install the rhel-system-roles package, and see the /usr/share/doc/rhel-system-roles/nbde_client/ and /usr/share/ansible/roles/rhel-system-roles.nbde_client/ directories.

11.19. Additional resources

tang(8), clevis(1), jose(1), and clevis-luks-unlockers(7) man pages
How to set up Network-Bound Disk Encryption with multiple LUKS devices (Clevis + Tang unlocking) Knowledgebase article

Chapter 12. Auditing the system

Audit does not provide additional security to your system; rather, it can be used to discover violations of security policies used on your system. These violations can further be prevented by additional security measures such as SELinux.

12.1. Linux Audit

The Linux Audit system provides a way to track security-relevant information on your system. Based on pre-configured rules, Audit generates log entries to record as much information about the events that are happening on your system as possible. This information is crucial for mission-critical environments to determine the violator of the security policy and the actions they performed.

The following list summarizes some of the information that Audit is capable of recording in its log files:

Date and time, type, and outcome of an event.
Sensitivity labels of subjects and objects.
Association of an event with the identity of the user who triggered the event.
All modifications to Audit configuration and attempts to access Audit log files.
All uses of authentication mechanisms, such as SSH, Kerberos, and others.
Changes to any trusted database, such as /etc/passwd.
Attempts to import or export information into or from the system.
Include or exclude events based on user identity, subject and object labels, and other attributes.

The use of the Audit system is also a requirement for a number of security-related certifications. Audit is designed to meet or exceed the requirements of the following certifications or compliance guides:

Controlled Access Protection Profile (CAPP)
Labeled Security Protection Profile (LSPP)
Rule Set Base Access Control (RSBAC)
National Industrial Security Program Operating Manual (NISPOM)
Federal Information Security Management Act (FISMA)
Payment Card Industry — Data Security Standard (PCI-DSS)
Security Technical Implementation Guides (STIG)

Audit has also been:

Evaluated by National Information Assurance Partnership (NIAP) and Best Security Industries (BSI).
Certified to LSPP/CAPP/RSBAC/EAL4+ on Red Hat Enterprise Linux 5.
Certified to Operating System Protection Profile / Evaluation Assurance Level 4+ (OSPP/EAL4+) on Red Hat Enterprise Linux 6.

Use Cases

Watching file access: Audit can track whether a file or a directory has been accessed, modified, executed, or the file’s attributes have been changed. This is useful, for example, to detect access to important files and have an Audit trail available in case one of these files is corrupted.
Monitoring system calls: Audit can be configured to generate a log entry every time a particular system call is used. This can be used, for example, to track changes to the system time by monitoring the settimeofday, clock_adjtime, and other time-related system calls.
Recording commands run by a user: Audit can track whether a file has been executed, so rules can be defined to record every execution of a particular command. For example, a rule can be defined for every executable in the /bin directory. The resulting log entries can then be searched by user ID to generate an audit trail of executed commands per user.
Recording execution of system pathnames: Aside from watching file access which translates a path to an inode at rule invocation, Audit can now watch the execution of a path even if it does not exist at rule invocation, or if the file is replaced after rule invocation. This allows rules to continue to work after upgrading a program executable or before it is even installed.
Recording security events: The pam_faillock authentication module is capable of recording failed login attempts. Audit can be set up to record failed login attempts as well and provides additional information about the user who attempted to log in.
Searching for events: Audit provides the ausearch utility, which can be used to filter the log entries and provide a complete audit trail based on several conditions.
Running summary reports: The aureport utility can be used to generate, among other things, daily reports of recorded events. A system administrator can then analyze these reports and investigate suspicious activity further.
Monitoring network access: The iptables and ebtables utilities can be configured to trigger Audit events, allowing system administrators to monitor network access.

Note

System performance may be affected depending on the amount of information that is collected by Audit.

12.2. Audit system architecture

The Audit system consists of two main parts: the user-space applications and utilities, and the kernel-side system call processing. The kernel component receives system calls from user-space applications and filters them through one of the following filters: user, task, fstype, or exit.

Once a system call passes the exclude filter, it is sent through one of the aforementioned filters, which, based on the Audit rule configuration, sends it to the Audit daemon for further processing.

The user-space Audit daemon collects the information from the kernel and creates entries in a log file. Other Audit user-space utilities interact with the Audit daemon, the kernel Audit component, or the Audit log files:

auditctl — the Audit control utility interacts with the kernel Audit component to manage rules and to control many settings and parameters of the event generation process.
The remaining Audit utilities take the contents of the Audit log files as input and generate output based on user’s requirements. For example, the aureport utility generates a report of all recorded events.

In RHEL 8, the Audit dispatcher daemon (audisp) functionality is integrated in the Audit daemon (auditd). Configuration files of plugins for the interaction of real-time analytical programs with Audit events are located in the /etc/audit/plugins.d/ directory by default.

12.3. Configuring auditd for a secure environment

The default auditd configuration should be suitable for most environments. However, if your environment has to meet strict security policies, the following settings are suggested for the Audit daemon configuration in the /etc/audit/auditd.conf file:

log_file: The directory that holds the Audit log files (usually /var/log/audit/) should reside on a separate mount point. This prevents other processes from consuming space in this directory and provides accurate detection of the remaining space for the Audit daemon.
max_log_file: Specifies the maximum size of a single Audit log file, must be set to make full use of the available space on the partition that holds the Audit log files.
max_log_file_action: Decides what action is taken once the limit set in max_log_file is reached, should be set to keep_logs to prevent Audit log files from being overwritten.
space_left: Specifies the amount of free space left on the disk for which an action that is set in the space_left_action parameter is triggered. Must be set to a number that gives the administrator enough time to respond and free up disk space. The space_left value depends on the rate at which the Audit log files are generated.
space_left_action: It is recommended to set the space_left_action parameter to email or exec with an appropriate notification method.
admin_space_left: Specifies the absolute minimum amount of free space for which an action that is set in the admin_space_left_action parameter is triggered, must be set to a value that leaves enough space to log actions performed by the administrator.
admin_space_left_action: Should be set to single to put the system into single-user mode and allow the administrator to free up some disk space.
disk_full_action: Specifies an action that is triggered when no free space is available on the partition that holds the Audit log files, must be set to halt or single. This ensures that the system is either shut down or operating in single-user mode when Audit can no longer log events.
disk_error_action: Specifies an action that is triggered in case an error is detected on the partition that holds the Audit log files, must be set to syslog, single, or halt, depending on your local security policies regarding the handling of hardware malfunctions.
flush: Should be set to incremental_async. It works in combination with the freq parameter, which determines how many records can be sent to the disk before forcing a hard synchronization with the hard drive. The freq parameter should be set to 100. These parameters assure that Audit event data is synchronized with the log files on the disk while keeping good performance for bursts of activity.

The remaining configuration options should be set according to your local security policy.

12.4. Starting and controlling auditd

Once auditd is configured, start the service to collect Audit information and store it in the log files. Use the following command as the root user to start auditd:

# service auditd start

To configure auditd to start at boot time:

# systemctl enable auditd

A number of other actions can be performed on auditd using the service auditd action command, where action can be one of the following:

stop: Stops auditd.
restart: Restarts auditd.
reload or force-reload: Reloads the configuration of auditd from the /etc/audit/auditd.conf file.
rotate: Rotates the log files in the /var/log/audit/ directory.
resume: Resumes logging of Audit events after it has been previously suspended, for example, when there is not enough free space on the disk partition that holds the Audit log files.
condrestart or try-restart: Restarts auditd only if it is already running.
status: Displays the running status of auditd.

Note

The service command is the only way to correctly interact with the auditd daemon. You need to use the service command so that the auid value is properly recorded. You can use the systemctl command only for two actions: enable and status.

12.5. Understanding Audit log files

By default, the Audit system stores log entries in the /var/log/audit/audit.log file; if log rotation is enabled, rotated audit.log files are stored in the same directory.

Add the following Audit rule to log every attempt to read or modify the /etc/ssh/sshd_config file:

# auditctl -w /etc/ssh/sshd_config -p warx -k sshd_config

If the auditd daemon is running, for example, using the following command creates a new event in the Audit log file:

$ cat /etc/ssh/sshd_config

This event in the audit.log file looks as follows:

type=SYSCALL msg=audit(1364481363.243:24287): arch=c000003e syscall=2 success=no exit=-13 a0=7fffd19c5592 a1=0 a2=7fffd19c4b50 a3=a items=1 ppid=2686 pid=3538 auid=1000 uid=1000 gid=1000 euid=1000 suid=1000 fsuid=1000 egid=1000 sgid=1000 fsgid=1000 tty=pts0 ses=1 comm="cat" exe="/bin/cat" subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 key="sshd_config"
type=CWD msg=audit(1364481363.243:24287):  cwd="/home/shadowman"
type=PATH msg=audit(1364481363.243:24287): item=0 name="/etc/ssh/sshd_config" inode=409248 dev=fd:00 mode=0100600 ouid=0 ogid=0 rdev=00:00 obj=system_u:object_r:etc_t:s0  nametype=NORMAL cap_fp=none cap_fi=none cap_fe=0 cap_fver=0
type=PROCTITLE msg=audit(1364481363.243:24287) : proctitle=636174002F6574632F7373682F737368645F636F6E666967

The above event consists of four records, which share the same time stamp and serial number. Records always start with the type= keyword. Each record consists of several name=value pairs separated by a white space or a comma. A detailed analysis of the above event follows:

First Record

type=SYSCALL: The type field contains the type of the record. In this example, the SYSCALL value specifies that this record was triggered by a system call to the kernel.

msg=audit(1364481363.243:24287):

The msg field records:

a time stamp and a unique ID of the record in the form audit(time_stamp:ID). Multiple records can share the same time stamp and ID if they were generated as part of the same Audit event. The time stamp is using the Unix time format - seconds since 00:00:00 UTC on 1 January 1970.
various event-specific name=value pairs provided by the kernel or user-space applications.

arch=c000003e

The arch field contains information about the CPU architecture of the system. The value, c000003e, is encoded in hexadecimal notation. When searching Audit records with the ausearch command, use the -i or --interpret option to automatically convert hexadecimal values into their human-readable equivalents. The c000003e value is interpreted as x86_64.

syscall=2

The syscall field records the type of the system call that was sent to the kernel. The value, 2, can be matched with its human-readable equivalent in the /usr/include/asm/unistd_64.h file. In this case, 2 is the open system call. Note that the ausyscall utility allows you to convert system call numbers to their human-readable equivalents. Use the ausyscall --dump command to display a listing of all system calls along with their numbers. For more information, see the ausyscall(8) man page.

success=no

The success field records whether the system call recorded in that particular event succeeded or failed. In this case, the call did not succeed.

exit=-13

The exit field contains a value that specifies the exit code returned by the system call. This value varies for a different system call. You can interpret the value to its human-readable equivalent with the following command:

# ausearch --interpret --exit -13

Note that the previous example assumes that your Audit log contains an event that failed with exit code -13.

a0=7fffd19c5592, a1=0, a2=7fffd19c5592, a3=a

The a0 to a3 fields record the first four arguments, encoded in hexadecimal notation, of the system call in this event. These arguments depend on the system call that is used; they can be interpreted by the ausearch utility.

items=1

The items field contains the number of PATH auxiliary records that follow the syscall record.

ppid=2686

The ppid field records the Parent Process ID (PPID). In this case, 2686 was the PPID of the parent process such as bash.

pid=3538

The pid field records the Process ID (PID). In this case, 3538 was the PID of the cat process.

auid=1000

The auid field records the Audit user ID, that is the loginuid. This ID is assigned to a user upon login and is inherited by every process even when the user’s identity changes, for example, by switching user accounts with the su - john command.

uid=1000

The uid field records the user ID of the user who started the analyzed process. The user ID can be interpreted into user names with the following command: ausearch -i --uid UID.

gid=1000

The gid field records the group ID of the user who started the analyzed process.

euid=1000

The euid field records the effective user ID of the user who started the analyzed process.

suid=1000

The suid field records the set user ID of the user who started the analyzed process.

fsuid=1000

The fsuid field records the file system user ID of the user who started the analyzed process.

egid=1000

The egid field records the effective group ID of the user who started the analyzed process.

sgid=1000

The sgid field records the set group ID of the user who started the analyzed process.

fsgid=1000

The fsgid field records the file system group ID of the user who started the analyzed process.

tty=pts0

The tty field records the terminal from which the analyzed process was invoked.

ses=1

The ses field records the session ID of the session from which the analyzed process was invoked.

comm="cat"

The comm field records the command-line name of the command that was used to invoke the analyzed process. In this case, the cat command was used to trigger this Audit event.

exe="/bin/cat"

The exe field records the path to the executable that was used to invoke the analyzed process.

subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

The subj field records the SELinux context with which the analyzed process was labeled at the time of execution.

key="sshd_config"

The key field records the administrator-defined string associated with the rule that generated this event in the Audit log.

Second Record

type=CWD

In the second record, the type field value is CWD — current working directory. This type is used to record the working directory from which the process that invoked the system call specified in the first record was executed.

The purpose of this record is to record the current process’s location in case a relative path winds up being captured in the associated PATH record. This way the absolute path can be reconstructed.

msg=audit(1364481363.243:24287)

The msg field holds the same time stamp and ID value as the value in the first record. The time stamp is using the Unix time format - seconds since 00:00:00 UTC on 1 January 1970.

cwd="/home/user_name"

The cwd field contains the path to the directory in which the system call was invoked.

Third Record

type=PATH

In the third record, the type field value is PATH. An Audit event contains a PATH-type record for every path that is passed to the system call as an argument. In this Audit event, only one path (/etc/ssh/sshd_config) was used as an argument.

msg=audit(1364481363.243:24287):

The msg field holds the same time stamp and ID value as the value in the first and second record.

item=0

The item field indicates which item, of the total number of items referenced in the SYSCALL type record, the current record is. This number is zero-based; a value of 0 means it is the first item.

name="/etc/ssh/sshd_config"

The name field records the path of the file or directory that was passed to the system call as an argument. In this case, it was the /etc/ssh/sshd_config file.

inode=409248

The inode field contains the inode number associated with the file or directory recorded in this event. The following command displays the file or directory that is associated with the 409248 inode number:

# find / -inum 409248 -print
/etc/ssh/sshd_config

dev=fd:00

The dev field specifies the minor and major ID of the device that contains the file or directory recorded in this event. In this case, the value represents the /dev/fd/0 device.

mode=0100600

The mode field records the file or directory permissions, encoded in numerical notation as returned by the stat command in the st_mode field. See the stat(2) man page for more information. In this case, 0100600 can be interpreted as -rw-------, meaning that only the root user has read and write permissions to the /etc/ssh/sshd_config file.

ouid=0

The ouid field records the object owner’s user ID.

ogid=0

The ogid field records the object owner’s group ID.

rdev=00:00

The rdev field contains a recorded device identifier for special files only. In this case, it is not used as the recorded file is a regular file.

obj=system_u:object_r:etc_t:s0

The obj field records the SELinux context with which the recorded file or directory was labeled at the time of execution.

nametype=NORMAL

The nametype field records the intent of each path record’s operation in the context of a given syscall.

cap_fp=none

The cap_fp field records data related to the setting of a permitted file system-based capability of the file or directory object.

cap_fi=none

The cap_fi field records data related to the setting of an inherited file system-based capability of the file or directory object.

cap_fe=0

The cap_fe field records the setting of the effective bit of the file system-based capability of the file or directory object.

cap_fver=0

The cap_fver field records the version of the file system-based capability of the file or directory object.

Fourth Record

type=PROCTITLE: The type field contains the type of the record. In this example, the PROCTITLE value specifies that this record gives the full command-line that triggered this Audit event, triggered by a system call to the kernel.
proctitle=636174002F6574632F7373682F737368645F636F6E666967: The proctitle field records the full command-line of the command that was used to invoke the analyzed process. The field is encoded in hexadecimal notation to not allow the user to influence the Audit log parser. The text decodes to the command that triggered this Audit event. When searching Audit records with the ausearch command, use the -i or --interpret option to automatically convert hexadecimal values into their human-readable equivalents. The 636174002F6574632F7373682F737368645F636F6E666967 value is interpreted as cat /etc/ssh/sshd_config.

12.6. Using auditctl for defining and executing Audit rules

The Audit system operates on a set of rules that define what is captured in the log files. Audit rules can be set either on the command line using the auditctl utility or in the /etc/audit/rules.d/ directory.

The auditctl command enables you to control the basic functionality of the Audit system and to define rules that decide which Audit events are logged.

File-system rules examples

To define a rule that logs all write access to, and every attribute change of, the /etc/passwd file:
```
# auditctl -w /etc/passwd -p wa -k passwd_changes
```
To define a rule that logs all write access to, and every attribute change of, all the files in the /etc/selinux/ directory:
```
# auditctl -w /etc/selinux/ -p wa -k selinux_changes
```

System-call rules examples

To define a rule that creates a log entry every time the adjtimex or settimeofday system calls are used by a program, and the system uses the 64-bit architecture:
```
# auditctl -a always,exit -F arch=b64 -S adjtimex -S settimeofday -k time_change
```
To define a rule that creates a log entry every time a file is deleted or renamed by a system user whose ID is 1000 or larger:
```
# auditctl -a always,exit -S unlink -S unlinkat -S rename -S renameat -F auid>=1000 -F auid!=4294967295 -k delete
```
Note that the -F auid!=4294967295 option is used to exclude users whose login UID is not set.

Executable-file rules

To define a rule that logs all execution of the /bin/id program, execute the following command:

# auditctl -a always,exit -F exe=/bin/id -F arch=b64 -S execve -k execution_bin_id

Additional resources

audictl(8) man page.

12.7. Defining persistent Audit rules

To define Audit rules that are persistent across reboots, you must either directly include them in the /etc/audit/rules.d/audit.rules file or use the augenrules program that reads rules located in the /etc/audit/rules.d/ directory.

Note that the /etc/audit/audit.rules file is generated whenever the auditd service starts. Files in /etc/audit/rules.d/ use the same auditctl command-line syntax to specify the rules. Empty lines and text following a hash sign (#) are ignored.

Furthermore, you can use the auditctl command to read rules from a specified file using the -R option, for example:

# auditctl -R /usr/share/audit/sample-rules/30-stig.rules

12.8. Using pre-configured rules files

In the /usr/share/audit/sample-rules directory, the audit package provides a set of pre-configured rules files according to various certification standards:

30-nispom.rules: Audit rule configuration that meets the requirements specified in the Information System Security chapter of the National Industrial Security Program Operating Manual.
30-ospp-v42*.rules: Audit rule configuration that meets the requirements defined in the OSPP (Protection Profile for General Purpose Operating Systems) profile version 4.2.
30-pci-dss-v31.rules: Audit rule configuration that meets the requirements set by Payment Card Industry Data Security Standard (PCI DSS) v3.1.
30-stig.rules: Audit rule configuration that meets the requirements set by Security Technical Implementation Guides (STIG).

To use these configuration files, copy them to the /etc/audit/rules.d/ directory and use the augenrules --load command, for example:

# cd /usr/share/audit/sample-rules/
# cp 10-base-config.rules 30-stig.rules 31-privileged.rules 99-finalize.rules /etc/audit/rules.d/
# augenrules --load

You can order Audit rules using a numbering scheme. See the /usr/share/audit/sample-rules/README-rules file for more information.

Additional resources

audit.rules(7) man page.

12.9. Using augenrules to define persistent rules

The augenrules script reads rules located in the /etc/audit/rules.d/ directory and compiles them into an audit.rules file. This script processes all files that end with .rules in a specific order based on their natural sort order. The files in this directory are organized into groups with the following meanings:

10 - Kernel and auditctl configuration
20 - Rules that could match general rules but you want a different match
30 - Main rules
40 - Optional rules
50 - Server-specific rules
70 - System local rules
90 - Finalize (immutable)

The rules are not meant to be used all at once. They are pieces of a policy that should be thought out and individual files copied to /etc/audit/rules.d/. For example, to set a system up in the STIG configuration, copy rules 10-base-config, 30-stig, 31-privileged, and 99-finalize.

Once you have the rules in the /etc/audit/rules.d/ directory, load them by running the augenrules script with the --load directive:

# augenrules --load
/sbin/augenrules: No change
No rules
enabled 1
failure 1
pid 742
rate_limit 0
...

Additional resources

audit.rules(8) and augenrules(8) man pages.

12.10. Disabling augenrules

Use the following steps to disable the augenrules utility. This switches Audit to use rules defined in the /etc/audit/audit.rules file.

Procedure

Copy the /usr/lib/systemd/system/auditd.service file to the /etc/systemd/system/ directory:
```
# cp -f /usr/lib/systemd/system/auditd.service /etc/systemd/system/
```
Edit the /etc/systemd/system/auditd.service file in a text editor of your choice, for example:
```
# vi /etc/systemd/system/auditd.service
```
Comment out the line containing augenrules, and uncomment the line containing the auditctl -R command:
```
#ExecStartPost=-/sbin/augenrules --load
ExecStartPost=-/sbin/auditctl -R /etc/audit/audit.rules
```
Reload the systemd daemon to fetch changes in the auditd.service file:
```
# systemctl daemon-reload
```
Restart the auditd service:
```
# service auditd restart
```

Additional resources

augenrules(8) and audit.rules(8) man pages.
Auditd service restart overrides changes made to /etc/audit/audit.rules.

Chapter 13. Blocking and allowing applications using fapolicyd

Setting and enforcing a policy that either allows or denies application execution based on a rule set efficiently prevents the execution of unknown and potentially malicious software.

13.1. Introduction to fapolicyd

The fapolicyd software framework controls the execution of applications based on a user-defined policy. This is one of the most efficient ways to prevent running untrusted and possibly malicious applications on the system.

The fapolicyd framework provides the following components:

fapolicyd service
fapolicyd command-line utilities
fapolicyd RPM plugin
fapolicyd rule language

The administrator can define the allow and deny execution rules for any application with the possibility of auditing based on a path, hash, MIME type, or trust.

The fapolicyd framework introduces the concept of trust. An application is trusted when it is properly installed by the system package manager, and therefore it is registered in the system RPM database. The fapolicyd daemon uses the RPM database as a list of trusted binaries and scripts. The fapolicyd RPM plugin registers any system update that is handled by either the YUM package manager or the RPM Package Manager. The plugin notifies the fapolicyd daemon about changes in this database. Other ways of adding applications require the creation of custom rules and restarting the fapolicyd service.

The fapolicyd service configuration is located in the /etc/fapolicyd/ directory with the following structure:

The fapolicyd.rules file contains allow and deny execution rules.
The fapolicyd.conf file contains daemon’s configuration options. This file is useful primarily for performance-tuning purposes.

You can use one of the ways for fapolicyd integrity checking:

file-size checking
comparing SHA-256 hashes
Integrity Measurement Architecture (IMA) subsystem

By default, fapolicyd does no integrity checking. Integrity checking based on the file size is fast, but an attacker can replace the content of the file and preserve its byte size. Computing and checking SHA-256 checksums is more secure, but it affects the performance of the system. The integrity = ima option in fapolicyd.conf requires support for files extended attributes (also known as xattr) on all file systems containing executable files.

Additional resources

fapolicyd(8), fapolicyd.rules(5), and fapolicyd.conf(5) man pages.
The Enhancing security with the kernel integrity subsystem chapter in the RHEL 8 Managing, monitoring, and updating the kernel document.

13.2. Deploying fapolicyd

To deploy the fapolicyd framework in RHEL:

Procedure

Install the fapolicyd package:
```
# yum install fapolicyd
```
Enable and start the fapolicyd service:
```
# systemctl enable --now fapolicyd
```

Verification

Verify that the fapolicyd service is running correctly:

# systemctl status fapolicyd
● fapolicyd.service - File Access Policy Daemon
   Loaded: loaded (/usr/lib/systemd/system/fapolicyd.service; enabled; vendor p>
   Active: active (running) since Tue 2019-10-15 18:02:35 CEST; 55s ago
  Process: 8818 ExecStart=/usr/sbin/fapolicyd (code=exited, status=0/SUCCESS)
 Main PID: 8819 (fapolicyd)
    Tasks: 4 (limit: 11500)
   Memory: 78.2M
   CGroup: /system.slice/fapolicyd.service
           └─8819 /usr/sbin/fapolicyd

Oct 15 18:02:35 localhost.localdomain systemd[1]: Starting File Access Policy D>
Oct 15 18:02:35 localhost.localdomain fapolicyd[8819]: Initialization of the da>
Oct 15 18:02:35 localhost.localdomain fapolicyd[8819]: Reading RPMDB into memory
Oct 15 18:02:35 localhost.localdomain systemd[1]: Started File Access Policy Da>
Oct 15 18:02:36 localhost.localdomain fapolicyd[8819]: Creating database

Log in as a user without root privileges, and check that fapolicyd is working, for example:
```
$ cp /bin/ls /tmp
$ /tmp/ls
bash: /tmp/ls: Operation not permitted
```

13.3. Marking files as trusted using an additional source of trust

You can use this procedure for using an additional source of trust for fapolicyd. Before RHEL 8.3, fapolicyd trusted only files contained in the RPM database. The fapolicyd framework now supports also use of the /etc/fapolicyd/fapolicyd.trust plain-text file as a source of trust. You can either modify fapolicyd.trust directly with a text editor or through fapolicyd CLI commands.

Note

Prefer marking files as trusted using fapolicyd.trust instead of writing custom fapolicyd rules.

Prerequisites

The fapolicyd framework is deployed on your system.

Procedure

Copy your custom binary to the required directory, for example:

$ cp /bin/ls /tmp
$ /tmp/ls
bash: /tmp/ls: Operation not permitted

Mark your custom binary as trusted:
```
# fapolicyd-cli --file add /tmp/ls
```
Note that previous command add the corresponding line to /etc/fapolicyd/fapolicyd.trust.
Update the fapolicyd database:
```
# fapolicyd-cli --update
```
Restart fapolicyd:
```
# systemctl restart fapolicyd
```

Verification

Check that your custom binary can be now executed, for example:
```
$ /tmp/ls
ls
```

Additional resources

fapolicyd.trust(5) man page.

13.4. Adding custom allow and deny rules for fapolicyd

The default set of rules in the fapolicyd package does not affect system functions. For custom scenarios, such as storing binaries and scripts in a non-standard directory or adding applications without the yum or rpm installers, you must modify existing or add new rules. The following steps demonstrate adding a new rule to allow a custom binary.

Prerequisites

The fapolicyd framework is deployed on your system.

Procedure

Copy your custom binary to the required directory, for example:

$ cp /bin/ls /tmp
$ /tmp/ls
bash: /tmp/ls: Operation not permitted

Stop the fapolicyd service:
```
# systemctl stop fapolicyd
```
Use debug mode to identify a corresponding rule. Because the output of the fapolicyd --debug command is verbose and you can stop it only by pressing Ctrl+C or killing the corresponding process, redirect the error output to a file:
```
# fapolicyd --debug 2> fapolicy.output &
[1] 51341
```
Alternatively, you can run fapolicyd debug mode in another terminal.

Repeat the command that was not permitted:

$ /tmp/ls
bash: /tmp/ls: Operation not permitted

Stop debug mode by resuming it in the foreground and pressing Ctrl+C:

# fg
fapolicyd --debug
^Cshutting down...
Inter-thread max queue depth 1
Allowed accesses: 2
Denied accesses: 1
[...]

Alternatively, kill the process of fapolicyd debug mode:

# kill 51341

Find a rule that denies the execution of your application:

# cat fapolicy.output
[...]
rule:9 dec=deny_audit perm=execute auid=1000 pid=51362 exe=/usr/bin/bash : file=/tmp/ls ftype=application/x-executable
[...]

Add a new allow rule before the rule that denied the execution of your custom binary in the /etc/fapolicyd/fapolicyd.rules file. The output of the previous command indicated that the rule is the rule number 9 in this example:
```
allow perm=execute exe=/usr/bin/bash trust=1 : path=/tmp/ls ftype=application/x-executable trust=0
```
Alternatively, you can allow executions of all binaries in the /tmp directory by adding the following rule in the /etc/fapolicyd/fapolicyd.rules file:
```
allow perm=execute exe=/usr/bin/bash trust=1 : dir=/tmp/ all trust=0
```

To prevent changes in the content of your custom binary, define the required rule using an SHA-256 checksum:

$ sha256sum /tmp/ls
780b75c90b2d41ea41679fcb358c892b1251b68d1927c80fbc0d9d148b25e836  ls

Change the rule to the following definition:

allow perm=execute exe=/usr/bin/bash trust=1 : sha256hash=780b75c90b2d41ea41679fcb358c892b1251b68d1927c80fbc0d9d148b25e836

Start the fapolicyd service:
```
# systemctl start fapolicyd
```

Verification

Check that your custom binary can be now executed, for example:
```
$ /tmp/ls
ls
```

Additional resources

fapolicyd.trust(5) man page.

13.5. Enabling fapolicyd integrity checks

By default, fapolicyd does not perform integrity checking. You can configure fapolicyd to perform integrity checks by comparing either file sizes or SHA-256 hashes. You can also set integrity checks by using the Integrity Measurement Architecture (IMA) subsystem.

Prerequisites

The fapolicyd framework is deployed on your system.

Procedure

Open the /etc/fapolicyd/fapolicyd.conf file in a text editor of your choice, for example:
```
# vi /etc/fapolicyd/fapolicyd.conf
```
Change the value of the integrity option from none to sha256, save the file, and exit the editor:
```
integrity = sha256
```
Restart the fapolicyd service:
```
# systemctl restart fapolicyd
```

Verification

Back up the file used for the verification:
```
# cp /bin/more /bin/more.bak
```
Change the content of the /bin/more binary:
```
# cat /bin/less > /bin/more
```

Use the changed binary as a regular user:

# su example.user
$ /bin/more /etc/redhat-release
bash: /bin/more: Operation not permitted

Revert the changes:
```
# mv -f /bin/more.bak /bin/more
```

13.7. Additional resources

fapolicyd-related man pages listed by using the man -k fapolicyd command.
The FOSDEM 2020 fapolicyd presentation.

Chapter 14. Protecting systems against intrusive USB devices

USB devices can be loaded with spyware, malware, or Trojans, which can steal your data or damage your system. As a Red Hat Enterprise Linux administrator, you can prevent such USB attacks with USBGuard.

14.1. USBGuard

With the USBGuard software framework, you can protect your systems against intrusive USB devices by using basic lists of permitted and forbidden devices based on the USB device authorization feature in the kernel.

The USBGuard framework provides the following components:

The system service component with an inter-process communication (IPC) interface for dynamic interaction and policy enforcement
The command-line interface to interact with a running usbguard system service
The rule language for writing USB device authorization policies
The C++ API for interacting with the system service component implemented in a shared library

The usbguard system service configuration file (/etc/usbguard/usbguard-daemon.conf) includes the options to authorize the users and groups to use the IPC interface.

Important

The system service provides the USBGuard public IPC interface. In Red Hat Enterprise Linux, the access to this interface is limited to the root user only by default.

Consider setting either the IPCAccessControlFiles option (recommended) or the IPCAllowedUsers and IPCAllowedGroups options to limit access to the IPC interface.

Ensure that you do not leave the Access Control List (ACL) unconfigured as this exposes the IPC interface to all local users and allows them to manipulate the authorization state of USB devices and modify the USBGuard policy.

14.2. Installing USBGuard

Use this procedure to install and initiate the USBGuard framework.

Procedure

Install the usbguard package:
```
# yum install usbguard
```

Create an initial rule set:

# usbguard generate-policy > /etc/usbguard/rules.conf

Start the usbguard daemon and ensure that it starts automatically on boot:
```
# systemctl enable --now usbguard
```

Verification

Verify that the usbguard service is running:

# systemctl status usbguard
● usbguard.service - USBGuard daemon
   Loaded: loaded (/usr/lib/systemd/system/usbguard.service; enabled; vendor preset: disabled)
   Active: active (running) since Thu 2019-11-07 09:44:07 CET; 3min 16s ago
     Docs: man:usbguard-daemon(8)
 Main PID: 6122 (usbguard-daemon)
    Tasks: 3 (limit: 11493)
   Memory: 1.2M
   CGroup: /system.slice/usbguard.service
           └─6122 /usr/sbin/usbguard-daemon -f -s -c /etc/usbguard/usbguard-daemon.conf

Nov 07 09:44:06 localhost.localdomain systemd[1]: Starting USBGuard daemon...
Nov 07 09:44:07 localhost.localdomain systemd[1]: Started USBGuard daemon.

List USB devices recognized by USBGuard:

# usbguard list-devices
4: allow id 1d6b:0002 serial "0000:02:00.0" name "xHCI Host Controller" hash...

Additional resources

usbguard(1) and usbguard-daemon.conf(5) man pages.

14.3. Blocking and authorizing a USB device using CLI

This procedure outlines how to authorize and block a USB device using the usbguard command.

Prerequisites

The usbguard service is installed and running.

Procedure

List USB devices recognized by USBGuard:

# usbguard list-devices
1: allow id 1d6b:0002 serial "0000:00:06.7" name "EHCI Host Controller" hash "JDOb0BiktYs2ct3mSQKopnOOV2h9MGYADwhT+oUtF2s=" parent-hash "4PHGcaDKWtPjKDwYpIRG722cB9SlGz9l9Iea93+Gt9c=" via-port "usb1" with-interface 09:00:00
...
6: block id 1b1c:1ab1 serial "000024937962" name "Voyager" hash "CrXgiaWIf2bZAU+5WkzOE7y0rdSO82XMzubn7HDb95Q=" parent-hash "JDOb0BiktYs2ct3mSQKopnOOV2h9MGYADwhT+oUtF2s=" via-port "1-3" with-interface 08:06:50

Authorize the device 6 to interact with the system:
```
# usbguard allow-device 6
```
Deauthorize and remove the device 6:
```
# usbguard reject-device 6
```
Deauthorize and retain the device 6:
```
# usbguard block-device 6
```

Note

USBGuard uses the block and reject terms with the following meanings:

block: do not interact with this device for now.
reject: ignore this device as if it does not exist.

Additional resources

usbguard(1) man page.
Built-in help listed by using the usbguard --help command.

14.4. Permanently blocking and authorizing a USB device

You can permanently block and authorize a USB device using the -p option. This adds a device-specific rule to the current policy.

Prerequisites

The usbguard service is installed and running.

Procedure

Configure SELinux to allow the usbguard daemon to write rules.

Display the semanage Booleans relevant to usbguard.

# semanage boolean -l | grep usbguard
usbguard_daemon_write_conf     (off  ,  off)  Allow usbguard to daemon write conf
usbguard_daemon_write_rules    (on   ,   on)  Allow usbguard to daemon write rules

Optional: If the usbguard_daemon_write_rules Boolean is turned off, turn it on.
```
# semanage boolean -m --on usbguard_daemon_write_rules
```

List USB devices recognized by USBGuard:

# usbguard list-devices
1: allow id 1d6b:0002 serial "0000:00:06.7" name "EHCI Host Controller" hash "JDOb0BiktYs2ct3mSQKopnOOV2h9MGYADwhT+oUtF2s=" parent-hash "4PHGcaDKWtPjKDwYpIRG722cB9SlGz9l9Iea93+Gt9c=" via-port "usb1" with-interface 09:00:00
...
6: block id 1b1c:1ab1 serial "000024937962" name "Voyager" hash "CrXgiaWIf2bZAU+5WkzOE7y0rdSO82XMzubn7HDb95Q=" parent-hash "JDOb0BiktYs2ct3mSQKopnOOV2h9MGYADwhT+oUtF2s=" via-port "1-3" with-interface 08:06:50

Permanently authorize the device 6 to interact with the system:
```
# usbguard allow-device 6 -p
```
Permanently deauthorize and remove the device 6:
```
# usbguard reject-device 6 -p
```
Permanently deauthorize and retain the device 6:
```
# usbguard block-device 6 -p
```

Note

USBGuard uses the terms block and reject with the following meanings:

block: do not interact with this device for now.
reject: ignore this device as if it does not exist.

Verification

Check that USBGuard rules include the changes you made.
```
# usbguard list-rules
```

Additional resources

usbguard(1) man page.
Built-in help listed by using the usbguard --help command.

14.5. Creating a custom policy for USB devices

The following procedure contains steps for creating a rule set for USB devices that reflects the requirements of your scenario.

Prerequisites

The usbguard service is installed and running.
The /etc/usbguard/rules.conf file contains an initial rule set generated by the usbguard generate-policy command.

Procedure

Create a policy which authorizes the currently connected USB devices, and store the generated rules to the rules.conf file:
```
# usbguard generate-policy --no-hashes > ./rules.conf
```
The --no-hashes option does not generate hash attributes for devices. Avoid hash attributes in your configuration settings because they might not be persistent.
Edit the rules.conf file with a text editor of your choice, for example:
```
# vi ./rules.conf
```
Add, remove, or edit the rules as required. For example, the following rule allows only devices with a single mass storage interface to interact with the system:
```
allow with-interface equals { 08:*:* }
```
See the usbguard-rules.conf(5) man page for a detailed rule-language description and more examples.

Install the updated policy:

# install -m 0600 -o root -g root rules.conf /etc/usbguard/rules.conf

Restart the usbguard daemon to apply your changes:
```
# systemctl restart usbguard
```

Verification

Check that your custom rules are in the active policy, for example:
```
# usbguard list-rules
...
4: allow with-interface 08:*:*
...
```

Additional resources

usbguard-rules.conf(5) man page.

14.6. Creating a structured custom policy for USB devices

You can organize your custom USBGuard policy in several .conf files within the /etc/usbguard/rules.d/ directory. The usbguard-daemon then combines the main rules.conf file with the .conf files within the directory in alphabetical order.

Prerequisites

The usbguard service is installed and running.

Procedure

Create a policy which authorizes the currently connected USB devices, and store the generated rules to a new .conf file, for example, policy.conf.
```
# usbguard generate-policy --no-hashes > ./policy.conf
```
The --no-hashes option does not generate hash attributes for devices. Avoid hash attributes in your configuration settings because they might not be persistent.

Display the policy.conf file with a text editor of your choice, for example:

# vi ./policy.conf
...
allow id 04f2:0833 serial "" name "USB Keyboard" via-port "7-2" with-interface { 03:01:01 03:00:00 } with-connect-type "unknown"
...

Move selected lines into a separate .conf file.
Note
The two digits at the beginning of the file name specify the order in which the daemon reads the configuration files.
For example, copy the rules for your keyboards into a new .conf file.
```
# grep "USB Keyboard" ./policy.conf > ./10keyboards.conf
```

Install the new policy to the /etc/usbguard/rules.d/ directory.

# install -m 0600 -o root -g root 10keyboards.conf /etc/usbguard/rules.d/10keyboards.conf

Move the rest of the lines to a main rules.conf file.

# grep -v "USB Keyboard" ./policy.conf > ./rules.conf

Install the remaining rules.

# install -m 0600 -o root -g root rules.conf /etc/usbguard/rules.conf

Restart the usbguard daemon to apply your changes.
```
# systemctl restart usbguard
```

Verification

Display all active USBGuard rules.

# usbguard list-rules
...
15: allow id 04f2:0833 serial "" name "USB Keyboard" hash "kxM/iddRe/WSCocgiuQlVs6Dn0VEza7KiHoDeTz0fyg=" parent-hash "2i6ZBJfTl5BakXF7Gba84/Cp1gslnNc1DM6vWQpie3s=" via-port "7-2" with-interface { 03:01:01 03:00:00 } with-connect-type "unknown"
...

Display the contents of the rules.conf file and all the .conf files in the /etc/usbguard/rules.d/ directory.
```
# cat /etc/usbguard/rules.conf /etc/usbguard/rules.d/*.conf
```
Verify that the active rules contain all the rules from the files and are in the correct order.

Additional resources

usbguard-rules.conf(5) man page.

14.7. Authorizing users and groups to use the USBGuard IPC interface

Use this procedure to authorize a specific user or a group to use the USBGuard public IPC interface. By default, only the root user can use this interface.

Prerequisites

The usbguard service is installed and running.
The /etc/usbguard/rules.conf file contains an initial rule set generated by the usbguard generate-policy command.

Procedure

Edit the /etc/usbguard/usbguard-daemon.conf file with a text editor of your choice:
```
# vi /etc/usbguard/usbguard-daemon.conf
```
For example, add a line with a rule that allows all users in the wheel group to use the IPC interface, and save the file:
```
IPCAllowGroups=wheel
```
You can add users or groups also with the usbguard command. For example, the following command enables the joesec user to have full access to the Devices and Exceptions sections. Furthermore, joesec can list the current policy and listen to policy signals.
```
# usbguard add-user joesec --devices ALL --policy list,listen --exceptions ALL
```
To remove the granted permissions for the joesec user, use the usbguard remove-user joesec command.
Restart the usbguard daemon to apply your changes:
```
# systemctl restart usbguard
```

Additional resources

usbguard(1) and usbguard-rules.conf(5) man pages.

14.8. Logging USBguard authorization events to the Linux Audit log

Use the following steps to integrate logging of USBguard authorization events to the standard Linux Audit log. By default, the usbguard daemon logs events to the /var/log/usbguard/usbguard-audit.log file.

Prerequisites

The usbguard service is installed and running.
The auditd service is running.

Procedure

Edit the usbguard-daemon.conf file with a text editor of your choice:
```
# vi /etc/usbguard/usbguard-daemon.conf
```
Change the AuditBackend option from FileAudit to LinuxAudit:
```
AuditBackend=LinuxAudit
```
Restart the usbguard daemon to apply the configuration change:
```
# systemctl restart usbguard
```

Verification

Query the audit daemon log for a USB authorization event, for example:
```
# ausearch -ts recent -m USER_DEVICE
```

Additional resources

usbguard-daemon.conf(5) man page.

14.9. Additional resources

usbguard(1), usbguard-rules.conf(5), usbguard-daemon(8), and usbguard-daemon.conf(5) man pages.
USBGuard Homepage.

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Red Hat Training

Security hardening

Securing Red Hat Enterprise Linux 8

Making open source more inclusive

Providing feedback on Red Hat documentation

Chapter 1. Overview of security hardening in RHEL

1.1. What is computer security?

1.2. Standardizing security

1.3. Cryptographic software and certifications

1.4. Security controls

1.4.1. Physical controls

1.4.2. Technical controls

1.4.3. Administrative controls

1.5. Vulnerability assessment

1.5.1. Defining assessment and testing

1.5.2. Establishing a methodology for vulnerability assessment

1.5.3. Vulnerability assessment tools

1.6. Security threats

1.6.1. Threats to network security

1.6.2. Threats to server security

1.6.3. Threats to workstation and home PC security

1.7. Common exploits and attacks

Chapter 2. Securing RHEL during installation

2.1. BIOS and UEFI security

2.1.1. BIOS passwords

2.1.2. Non-BIOS-based systems security

2.2. Disk partitioning

2.3. Restricting network connectivity during the installation process

2.4. Installing the minimum amount of packages required

2.5. Post-installation procedures

Chapter 3. Installing a RHEL 8 system with FIPS mode enabled

3.1. Federal Information Processing Standard (FIPS)

3.2. Installing the system with FIPS mode enabled

3.3. Additional resources

Chapter 4. Using system-wide cryptographic policies

4.1. System-wide cryptographic policies

Tool for managing crypto policies

Strong crypto defaults by removing insecure cipher suites and protocols

Cipher suites and protocols disabled in all policy levels

Cipher suites and protocols enabled in the crypto-policies levels

4.2. Switching the system-wide cryptographic policy to mode compatible with earlier releases

4.3. Switching the system to FIPS mode

4.4. Enabling FIPS mode in a container

4.4.1. Enabling FIPS mode in a container in RHEL 8.2

4.4.2. Enabling FIPS mode in a container in RHEL 8.1 and earlier

4.5. List of RHEL applications using cryptography that is not compliant with FIPS 140-2

4.6. Excluding an application from following system-wide crypto policies

4.6.1. Examples of opting out of system-wide crypto policies

4.7. Customizing system-wide cryptographic policies with policy modifiers

4.8. Disabling SHA-1 by customizing a system-wide cryptographic policy

4.9. Creating and setting a custom system-wide cryptographic policy

4.10. Related information

Chapter 5. Setting a custom cryptographic policy across systems

5.1. Crypto Policies System Role variables and facts

5.2. Setting a custom cryptographic policy using the Crypto Policies System Role

5.3. Additional resources

Chapter 6. Configuring applications to use cryptographic hardware through PKCS #11

6.1. Cryptographic hardware support through PKCS #11

6.2. Using SSH keys stored on a smart card

6.3. Configuring applications to authenticate using certificates from smart cards

6.4. Using HSMs protecting private keys in Apache

6.5. Using HSMs protecting private keys in Nginx

6.6. Related information

Chapter 7. Using shared system certificates

7.1. The system-wide trust store

7.2. Adding new certificates

7.3. Managing trusted system certificates

7.4. Additional resources

Chapter 8. Scanning the system for configuration compliance and vulnerabilities

8.1. Configuration compliance tools in RHEL

8.2. Vulnerability scanning

8.2.1. Red Hat Security Advisories OVAL feed

8.2.2. Scanning the system for vulnerabilities

8.2.3. Scanning remote systems for vulnerabilities

8.3. Configuration compliance scanning

8.3.1. Configuration compliance in RHEL 8

8.3.2. Possible results of an OpenSCAP scan

8.3.3. Viewing profiles for configuration compliance

8.3.4. Assessing configuration compliance with a specific baseline

8.4. Remediating the system to align with a specific baseline

9.2. Performing integrity checks with `AIDE`