RHSA-2021:0245MediumCVSS 4.0

Red Hat Security Advisory: dnsmasq security update

Published
January 25, 2021
Last Modified
November 5, 2026

🔗 CVE IDs covered (3)

CVE-2020-25684 →CVE-2020-25685 →CVE-2020-25686 →

📋 Description

CVE-2020-25684 — dnsmasq: loose address/port check in reply_query() makes forging replies easier for an off-path attacker CVE-2020-25685 — dnsmasq: loose query name check in reply_query() makes forging replies easier for an off-path attacker CVE-2020-25686 — dnsmasq: multiple queries forwarded for the same name makes forging replies easier for an off-path attacker

🎯 Affected products7

  • Red Hat Enterprise Linux Server AUS (v. 7.3)
  • Red Hat Enterprise Linux Server Optional AUS (v. 7.3)
  • dnsmasq-0:2.66-21.el7_3.3.src as a component of Red Hat Enterprise Linux Server AUS (v. 7.3)
  • dnsmasq-0:2.66-21.el7_3.3.x86_64 as a component of Red Hat Enterprise Linux Server AUS (v. 7.3)
  • dnsmasq-debuginfo-0:2.66-21.el7_3.3.x86_64 as a component of Red Hat Enterprise Linux Server AUS (v. 7.3)
  • dnsmasq-debuginfo-0:2.66-21.el7_3.3.x86_64 as a component of Red Hat Enterprise Linux Server Optional AUS (v. 7.3)
  • dnsmasq-utils-0:2.66-21.el7_3.3.x86_64 as a component of Red Hat Enterprise Linux Server Optional AUS (v. 7.3)

✅ Remediation

For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 Workaround: 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 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. Workaround: 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 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.

🔗 References (7)