CVE-2020-25686

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Last Modified: UTC

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

Description

A flaw was found in dnsmasq. When receiving a query, dnsmasq does not check for an existing pending request for the same name and forwards a new request. By default, a maximum of 150 pending queries can be sent to upstream servers, so there can be at most 150 queries for the same name. This flaw allows an off-path attacker on the network to substantially reduce the number of attempts that it would have to perform to forge a reply and have it accepted by dnsmasq. This issue is mentioned in the "Birthday Attacks" section of RFC5452. If chained with CVE-2020-25684, the attack complexity of a successful attack is reduced. The highest threat from this vulnerability is to data integrity.

Statement

Dnsmasq may be run by libvirt and/or NetworkManager. libvirt uses dnsmasq by default to provide DNS service to its guests. NetworkManager may be configured to use dnsmasq to provide DNS service to the system, if a line dns=dnsmasq is present in the [main] section of the configuration file /etc/NetworkManager/NetworkManager.conf.

In Red Hat OpenStack Platform (RHOSP) and Red Hat Virtualization (RHV), the dnsmasq package is provided by the underlying Red Hat Enterprise Linux (RHEL) product. RHOSP and RHV are therefore indirectly affected, so please ensure that the underlying RHEL dnsmasq package is updated.

Mitigation

The impact of this flaw can be reduced by disabling the dnsmasq cache by adding `--cache-size=0` when calling dnsmasq or by adding a line with `cache-size=0` to the dnsmasq configuration file (/etc/dnsmasq.conf by default).

When using Red Hat Enterprise Linux 8.3 with libvirt through a virt:rhel module, use `virsh net-edit <network-name>` and reference This content is not included.https://libvirt.org/formatnetwork.html#elementsNamespaces to add the suggested option `cache-size=0`.

There is no way to customize the dnsmasq configuration generated by libvirt, when using versions of Red Hat Enterprise Linux prior to version 8.3. If dnsmasq is being run through NetworkManager, create a new file in /etc/NetworkManager/dnsmasq.d/ and add `cache-size=0` to it.

In all cases, by disabling the cache, you may experience a performance loss in your environment due to all DNS queries being forwarded to the upstream servers. Please evaluate if the mitigation is appropriate for the system’s environment before applying.

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2020-25686

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2020-25686

Content from www.jsof-tech.com is not included.https://www.jsof-tech.com/disclosures/dnspooq/

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Red Hat Enterprise Linux 5 dnsmasq Out of support scope
Red Hat Enterprise Linux 6 dnsmasq Out of support scope
Red Hat Enterprise Linux 7 dnsmasq Fixed RHSA-2021:0153
Red Hat Enterprise Linux 7.2 Advanced Update Support dnsmasq Fixed RHSA-2021:0240
Red Hat Enterprise Linux 7.3 Advanced Update Support dnsmasq Fixed RHSA-2021:0245
Red Hat Enterprise Linux 7.4 Advanced Update Support dnsmasq Fixed RHSA-2021:0156
Red Hat Enterprise Linux 7.4 Telco Extended Update Support dnsmasq Fixed RHSA-2021:0156
Red Hat Enterprise Linux 7.4 Update Services for SAP Solutions dnsmasq Fixed RHSA-2021:0156
Red Hat Enterprise Linux 7.6 Extended Update Support dnsmasq Fixed RHSA-2021:0155
Red Hat Enterprise Linux 7.7 Extended Update Support dnsmasq Fixed RHSA-2021:0154
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 4 3.7
Attack Vector Network Network
Attack Complexity High High
Privileges Required None None
User Interaction None None
Scope Changed Unchanged
Confidentiality Impact None None
Integrity Impact Low Low
Availability Impact None None

CVSS v3 Vector

Red Hat CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N

NVD CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Acknowledgements

Red Hat would like to thank Moshe Kol (JSOF) and Shlomi Oberman (JSOF) for reporting this issue.

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.

My product is listed as "Out of Support Scope". What does this mean?

 When a product is listed as "Out of Support Scope", it means a vulnerability with the impact level assigned to this CVE is no longer covered by its current support lifecycle phase. The product has been identified to contain the impacted component, but analysis to determine whether it is affected or not by this vulnerability was not performed. The product should be assumed to be affected. Customers are advised to apply any mitigation options documented on this page, consider removing or disabling the impacted component, or upgrade to a supported version of the product that has an update available.