CVE-2026-16390: Mozilla Firefox

Critical severity, CVSS 9.1. EPSS: 0.3% chance of exploitation in the next 30 days.

Mitigation bypass in the Enterprise Policies component. This vulnerability was fixed in Firefox 153, Firefox ESR 140.13, Thunderbird 153, and Thunderbird 140.13.

Affected products

• Mozilla Firefox: before 140.13.0 (fixed in 140.13.0); before 153.0.0 (fixed in 153.0.0)
• Mozilla Thunderbird: before 140.13.0 (fixed in 140.13.0); from 141.0, before 153.0 (fixed in 153.0)

Published 2026-07-21. Last modified 2026-07-24.