Managing and monitoring security updates

Red Hat Enterprise Linux 9

Update RHEL 9 system security to prevent attackers from exploiting known flaws

Red Hat Customer Content Services

Abstract

Learn how to install security updates and display additional details about the updates to keep your Red Hat Enterprise Linux systems secured against newly discovered threats and vulnerabilities.

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Chapter 1. Identifying security updates

Keeping enterprise systems secure from current and future threats requires regular security updates. Red Hat Product Security provides the guidance you need to confidently deploy and maintain enterprise solutions.

1.1. What are security advisories?

Red Hat Security Advisories (RHSA) document the information about security flaws being fixed in Red Hat products and services.

Each RHSA includes the following information:

  • Severity
  • Type and status
  • Affected products
  • Summary of fixed issues
  • Links to the tickets about the problem. Note that not all tickets are public.
  • Common Vulnerabilities and Exposures (CVE) numbers and links with additional details, such as attack complexity.

Red Hat Customer Portal provides a list of Red Hat Security Advisories published by Red Hat. You can display details of a specific advisory by navigating to the advisory’s ID from the list of Red Hat Security Advisories.

Figure 1.1. List of security advisories

customer portal list security advisories rhel9

Optionally, you can also filter the results by specific product, variant, version, and architecture. For example, to display only advisories for Red Hat Enterprise Linux 9, you can set the following filters:

  • Product: Red Hat Enterprise Linux
  • Variant: All Variants
  • Version: 9
  • Optionally, select a minor version.

Additional resources

1.2. Displaying security updates that are not installed on a host

You can list all available security updates for your system by using the dnf utility.

Prerequisite

  • A Red Hat subscription attached to the host.

Procedure

  • List all available security updates which have not been installed on the host: 

    # dnf updateinfo list updates security
...
RHSA-2019:0997 Important/Sec. platform-python-3.6.8-2.el8_0.x86_64
RHSA-2019:0997 Important/Sec. python3-libs-3.6.8-2.el8_0.x86_64
RHSA-2019:0990 Moderate/Sec.  systemd-239-13.el8_0.3.x86_64
...

1.3. Displaying security updates that are installed on a host

You can list installed security updates for your system by using the dnf utility.

Procedure

  • List all security updates which are installed on the host: 

    # dnf updateinfo list security --installed
...
RHSA-2019:1234 Important/Sec. libssh2-1.8.0-7.module+el8+2833+c7d6d092
RHSA-2019:4567 Important/Sec. python3-libs-3.6.7.1.el8.x86_64
RHSA-2019:8901 Important/Sec. python3-libs-3.6.8-1.el8.x86_64
...

    If multiple updates of a single package are installed, dnf lists all advisories for the package. In the previous example, two security updates for the python3-libs package have been installed since the system installation.

1.4. Displaying a specific advisory using dnf

You can use the dnf utility to display a specific advisory information that is available for an update.

Prerequisites

Procedure

  • Display a specific advisory: 

    # dnf updateinfo info <Update ID>
====================================================================
  Important: python3 security update
====================================================================
  Update ID: RHSA-2019:0997
       Type: security
    Updated: 2019-05-07 05:41:52
       Bugs: 1688543 - CVE-2019-9636 python: Information Disclosure due to urlsplit improper NFKC normalization
       CVEs: CVE-2019-9636
Description: ...

    Replace the Update ID with the required advisory. For example, # dnf updateinfo info <RHSA-2019:0997>.

Chapter 2. Installing security updates

2.1. Installing all available security updates

To keep the security of your system up to date, you can install all currently available security updates using the dnf utility.

Prerequisite

  • A Red Hat subscription attached to the host.

Procedure

  1. Install security updates using dnf utility: 

    # dnf update --security
    Note

    The --security parameter is important. Without it, dnf update installs all updates, including bug fixes and enhancements.

  2. Confirm and start the installation by pressing y: 

    ...
Transaction Summary
===========================================
Upgrade  ... Packages

Total download size: ... M
Is this ok [y/d/N]: y

  3. Optional: list processes that require a manual restart of the system after installing the updated packages: 

    # dnf needs-restarting
1107 : /usr/sbin/rsyslogd -n
1199 : -bash
    Note

    This command lists only processes that require a restart, and not services. That is, you cannot restart processes listed using the systemctl utility. For example, the bash process in the output is terminated when the user that owns this process logs out.

2.2. Installing a security update provided by a specific advisory

In certain situations, you might want to install only specific updates. For example, if a specific service can be updated without scheduling a downtime, you can install security updates for only this service, and install the remaining security updates later.

Prerequisites

Procedure

  1. Install a specific advisory: 

    # dnf update --advisory=<Update_ID>

    Replace <Update_ID> with the ID of the security advisory that you want to update. For example: 

    # dnf update --advisory=RHSA-2019:0997
    Important

    You can update to apply a specific advisory with a minimal version change by using the dnf upgrade-minimal <Update_ID> command.

  2. Confirm and start the installation by pressing y: 

    ...
Transaction Summary
===========================================
Upgrade  ... Packages

Total download size: ... M
Is this ok [y/d/N]: y

  3. Optional: List the processes that require a manual restart of the system after installing the updated packages: 

    # dnf needs-restarting
1107 : /usr/sbin/rsyslogd -n
1199 : -bash
    Note

    This command lists only processes that require a restart, and not services. This means that you cannot restart all processes listed by using the systemctl utility. For example, the bash process in the output is terminated when the user that owns this process logs out.

2.3. Installing security updates automatically

Use to following procedure to update your system automatically with security updates.

Prerequisites

  • A Red Hat subscription attached to the host.

Procedure

  1. Install dnf-automatic using dnf 

    # dnf install dnf-automatic

  2. Confirm and start the installation by pressing y: 

    ...
Transaction Summary
===========================================
Upgrade  ... Packages
Total download size: ... M
Is this ok [y/d/N]: y

  3. Open the /etc/dnf/automatic.conf file in a text editor of your choice, for example: 

    # vi /etc/dnf/automatic.conf

  4. Configure the upgrade_type = security option in the [commands] section: 

    [commands]
#  What kind of upgrade to perform:
# default                            = all available upgrades
# security                           = only the security upgrades
upgrade_type = security
  5. Enable the systemd timer unit 
# systemctl enable --now dnf-automatic-install.timer

Additional resources

  • dnf-automatic(8) man page

2.4. Additional resources

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