CVE-2026-117906

A flaw was found in Firefox and Thunderbird. The Mozilla Foundation's Security Advisory describes the following issue: Use-after-free in the CSS Parsing and Computation 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 prevent use-after-free conditions in the CSS parsing and computation engine by validating object lifecycles during style computation: upgrade to Firefox 159, Firefox ESR 115.44, Firefox ESR 153.6 (or the corresponding fixed Red Hat builds), which remediates memory management handling to eliminate the use-after-free condition during CSS parsing and computation, closing all 2 injection vectors (crafted web page with malicious CSS, crafted HTML email rendering malicious CSS). Until patched, this is a concern on Users processing untrusted web content or HTML emails on any platform, so Avoid opening untrusted links or documents and restrict rendering of untrusted HTML emails with remote CSS. As a compensating measure, Enable Address Space Layout Randomization to randomize process memory and hinder predictable heap exploitation. These controls limit blast radius and contain exploitation, but they do not fix the underlying CSS parsing use-after-free defect — apply the upstream patch to fully remediate.

Highest-impact CME: CME-101 ASLR (Address Space Layout Randomization) (medium)