CVE-2026-16396: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 0.2% chance of exploitation in the next 30 days.

Privilege escalation in WebExtensions. 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.