CVE-2026-117865

A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: Use-after-free in the JavaScript: GC 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 (2026-11-02) --- 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 untrusted JavaScript execution within browser and application contexts to prevent triggering garbage collection memory corruption: upgrade to Firefox 159, Firefox ESR 153.6, and Thunderbird 159 (or the corresponding fixed Red Hat builds), which resolves the use-after-free memory corruption condition within the JavaScript garbage collection component, closing malicious JavaScript execution triggering garbage collection. Until patched, this is only a concern on Firefox and Thunderbird deployments running untrusted JavaScript in browser or application contexts — Standard Thunderbird email reading where scripting is disabled are unaffected — so Restrict execution of untrusted scripts and prevent users from browsing untrusted sites in contexts where JavaScript is enabled. As a compensating measure, Enable Address Space Layout Randomization to randomize process memory layout and hinder reliable exploitation of memory corruption. 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-1309 Script Engine Restriction (Sandbox / Disable) (high)