CVE-2019-18934

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Last Modified: UTC

Moderate Moderate Impact What does this mean?
5.6 CVSS v3 Base Score

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.

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2019-18934

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2019-18934

Content from nlnetlabs.nl is not included.https://nlnetlabs.nl/downloads/unbound/CVE-2019-18934.txt

Content from www.nlnetlabs.nl is not included.https://www.nlnetlabs.nl/news/2019/Nov/19/unbound-1.9.5-released/

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Red Hat Enterprise Linux 6 unbound Not affected
Red Hat Enterprise Linux 7 unbound Will not fix
Red Hat Enterprise Linux 8 unbound Fixed RHSA-2020:1716
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

Common Vulnerability Scoring System (CVSS) Score Details

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 Authorities (CNA) source for its products and services (see Red Hat classifications ).

CVSS v3 Score Breakdown Red Hat NVD
CVSS v3 Base Score 5.6 7.3
Attack Vector Network Network
Attack Complexity High Low
Privileges Required None None
User Interaction None None
Scope Unchanged Unchanged
Confidentiality Impact Low Low
Integrity Impact Low Low
Availability Impact Low Low

CVSS v3 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.

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

 For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?
  • "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

What can I do if my product is listed as "Will not fix"?

 A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.

What can I do if my product is listed as "Fix deferred"?

 A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Apply a mitigation (if one exists).
  • Open a This content is not included.support case to request a prioritization of releasing a fix for this vulnerability.
  • Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

 A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

I have a Red Hat product but it is not in the above list, is it affected?

 The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

 In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our This content is not included.Red Hat Vulnerability Scanner Certification program.