CVE-2026-74959: Mozilla Firefox

Critical severity, CVSS 9.1. EPSS: 0.5% chance of exploitation in the next 30 days.

Mitigation bypass in the Storage: Cache API component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, Firefox ESR 153.1, Thunderbird 154, Thunderbird 140.14, and Thunderbird 153.1.

Affected products

• Mozilla Firefox: before 140.14.0 (fixed in 140.14.0); from 141.0, before 153.1.0 (fixed in 153.1.0)
• Mozilla Thunderbird: before 140.14.0 (fixed in 140.14.0); from 141.0, before 153.1.0 (fixed in 153.1.0)

Published 2026-08-18. Last modified 2026-08-24.