CVE-2019-18934
Description
A shell command injection vulnerability was discovered in the way unbound handles DNS queries for systems with a public key used for IPsec. When ipsecmod is enabled, a malicious DNS server could send a DNS reply which would be used during a following DNS query to execute shell commands with the privileges of the unbound process. The same attack could be performed by an attacker who can modify data transmitted over the network, before it reaches the unbound server, if DNSSEC is not used.
Statement
The versions of unbound as shipped in Red Hat Enterprise Linux 7 and 8 have ipsecmod disabled by default, even though it could be activated through the unbound-control command, it would only be executable by high-privilege users. Moreover, the username option is enabled, reducing the impact of a successful attack, and DNSSEC is used by default, preventing an attacker from modifying DNS packets on the wire. Finally, the default SELinux policies prevent unbound from running any shell command.
Mitigation
* Do not enable ipsecmod in the unbound.conf configuration file nor via unbound-control, if DNSSEC based Opportunistic IPsec is not used.
* Use the `username` option in unbound.conf to make unbound drop privileges and reduce the impact of a successful attack.
* Enable SELinux to prevent unbound from executing shell commands, apart from the expected one specified in the `ipsecmod-hook` option.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.6 | 7.3 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | Low | Low | N/A |
| Integrity Impact | Low | Low | N/A |
| Availability Impact | Low | Low | N/A |
Vector
Red Hat: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
Red Hat CVSS v3 Score Explanation
Setting Attack Complexity to High (AC:H) as the attacker would need to setup a malicious DNS server that should be trusted by the vulnerable unbound service.
Understanding the Weakness (CWE)
Confidentiality,Integrity,Availability,Non-Repudiation
Technical Impact: Execute Unauthorized Code or Commands; DoS: Crash, Exit, or Restart; Read Files or Directories; Modify Files or Directories; Read Application Data; Modify Application Data; Hide Activities
Attackers could execute unauthorized operating system commands, which could then be used to disable the product, or read and modify data for which the attacker does not have permissions to access directly. Since the targeted application is directly executing the commands instead of the attacker, any malicious activities may appear to come from the application or the application's owner.
Frequently Asked Questions
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