CVE-2026-8958: Mozilla Firefox

High severity, CVSS 8.6. EPSS: 0.4% chance of exploitation in the next 30 days.

Information disclosure, sandbox escape in the Security: Process Sandboxing 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.