CVE-2026-117920

A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: Use-after-free in the DOM: HTML Parser component

Red Hat Product Security rates the severity of this flaw as determined by the Mozilla Foundation Security Advisory.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

--- CME Mitigation Guidance (2026-11-03) --- Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.

The highest-value action is to isolate or restrict DOM HTML parsing of untrusted web content to prevent dereferencing expired memory pointers: upgrade to Firefox 159 and Firefox ESR 153.6 (or the corresponding fixed Red Hat builds), which fixes use-after-free memory corruption during HTML parsing in the DOM component, closing crafted HTML content. Until patched, this is a concern on deployments running Firefox or Thunderbird on any platform, so prevent users from visiting untrusted websites and avoid opening untrusted HTML documents. As a compensating measure, ensure Address Space Layout Randomization is enabled to impede reliable code execution and ROP chain construction and run SELinux in enforcing mode to confine browser processes and limit system-level access. These controls limit blast radius and contain exploitation, but they do not fix the underlying use-after-free defect — apply the upstream patch to fully remediate.

Highest-impact CME: CME-301 SELinux (Enforcing Mode) (medium)