CVE-2026-4700 is a mitigation bypass vulnerability in the Networking: HTTP component of Mozilla Firefox. This vulnerability was resolved in Firefox 149 and Firefox ESR 140.9. The CVSS 3.1 base score is 9.8 (critical), with attack vector network, low attack complexity, no privileges or user interaction required, and impacts confidentiality, integrity, and availability. The vendor advisory confirms the fix is included in Firefox 149 and Firefox ESR 140.9. No known exploits in the wild have been reported at this time.

Successful exploitation of this vulnerability could allow an attacker to bypass security mitigations in the HTTP networking component, potentially leading to full compromise of confidentiality, integrity, and availability of the affected Firefox browser. Given the critical CVSS score and the nature of the mitigation bypass, this could enable remote code execution or other severe impacts if exploited.

Mozilla has released official fixes for this vulnerability in Firefox 149 and Firefox ESR 140.9. Users and administrators should update affected Firefox installations to version 149 or later, or Firefox ESR 140.9 or later, to remediate this vulnerability. No additional mitigation steps are indicated by the vendor advisory.