CVE-2026-16407 is a critical mitigation bypass vulnerability in the DOM: Service Workers component of Mozilla Firefox. The flaw allows an attacker to bypass security mitigations, potentially leading to full compromise of the affected system. This vulnerability was addressed and fixed in Firefox 153. The CVSS v3.1 base score is 9.8, with attack vector network, low attack complexity, no privileges required, no user interaction, and high impact on confidentiality, integrity, and availability. The vendor advisory confirms the fix in Firefox 153 and Thunderbird 153 and provides detailed references to the Mozilla security advisories.

Successful exploitation of this vulnerability could allow an attacker to bypass security mitigations in the Service Workers component, potentially leading to unauthorized access, privilege escalation, or other severe impacts on confidentiality, integrity, and availability of the affected system. Given the critical CVSS score of 9.8, the impact is considered critical.

A fix for this vulnerability is available and has been incorporated in Mozilla Firefox version 153. Users and administrators should update affected Firefox installations to version 153 or later to remediate this issue. For Thunderbird users, updating to version 153 or later also addresses this vulnerability. No additional mitigation steps are indicated by the vendor advisory.