CVE-2026-117883

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 eliminate use-after-free conditions by updating the DOM HTML parser component or avoiding processing of untrusted HTML documents: upgrade to Firefox 159, Firefox ESR 115.44, Firefox ESR 153.6 (or the corresponding fixed Red Hat builds), which remediates object lifecycle management in the DOM HTML parser component to prevent use-after-free conditions during document parsing, closing crafted HTML document parsing. Until patched, this is a concern on Systems running affected Firefox installations where users access untrusted web links or load untrusted HTML content, so Avoid navigating to untrusted links and restrict opening arbitrary or untrusted HTML documents in the browser. As a compensating measure, Ensure ASLR is enabled to randomize memory layout and hinder reliable exploitation of the parser memory corruption, Deploy builds with Full RELRO and PIE to enforce read-only relocations and impede code reuse or pointer overwrites, and Keep SELinux in Enforcing mode to confine the browser process and contain post-exploitation actions. These controls limit blast radius and contain exploitation, but they do not fix the underlying DOM HTML parser use-after-free defect — apply the upstream patch to fully remediate.

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