CVE-2026-8956: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 0.6% chance of exploitation in the next 30 days.

Integer overflow in the Networking: JAR component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.

Affected products

• Mozilla Firefox: before 140.11.0 (fixed in 140.11.0); before 151.0.0 (fixed in 151.0.0)
• Mozilla Thunderbird: before 140.11 (fixed in 140.11); before 151.0.0 (fixed in 151.0.0)

Published 2026-05-19. Last modified 2026-06-17.