CVE-2026-117866

A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: Privilege escalation due to use-after-free in the Graphics: Canvas2D 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 correct memory lifecycle and pointer management during Canvas2D graphics rendering in the browser process: upgrade to Firefox 159, Firefox ESR 115.44, and Firefox ESR 153.6 (or the corresponding fixed Red Hat builds), which resolves a use-after-free memory lifecycle flaw in the Graphics: Canvas2D component, closing all 2 injection vectors (malicious web page rendering crafted Canvas2D operations, crafted HTML email message rendering in Thunderbird). Until patched, this is a concern on deployments running affected Firefox or Thunderbird clients rendering untrusted web pages or HTML documents, so restrict users from navigating to untrusted websites or opening untrusted HTML documents and email messages in affected browsers. As a compensating measure, enable address space layout randomization to randomize browser process memory layout and hinder reliable exploitation and disable or harden JIT compilation in Firefox to restrict heap-spraying and code-generation primitives. 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-101 ASLR (Address Space Layout Randomization) (medium)