CVE-2026-117891

A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: Use-after-free in the JavaScript Engine: JIT 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 disable or restrict JIT compilation in Firefox (such as via javascript.options.ion) to eliminate the vulnerable JIT compiler code path: upgrade to Firefox 159, Firefox ESR 115.44, Firefox ESR 153.6 (or the corresponding fixed Red Hat builds), which resolves the use-after-free condition within the JavaScript Engine JIT compiler component, closing crafted JavaScript execution triggering JIT compiler use-after-free. Until patched, this is a concern on Users and systems running Firefox or Thunderbird processing untrusted web content, so Prevent browsing untrusted web pages, block execution of untrusted web content, and disable JIT compilation in browser preferences. As a compensating measure, Ensure system Address Space Layout Randomization is active to randomize memory layout and hinder reliable address calculation. These controls limit blast radius and contain exploitation, but they do not fix the underlying JIT engine use-after-free defect — apply the upstream patch to fully remediate.

Highest-impact CME: CME-919 JIT Compiler Hardening (JIT Restriction / V8 Sandbox) (high)