CVE-2026-12291: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 0.4% chance of exploitation in the next 30 days.

Use-after-free in the Networking: HTTP component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Firefox ESR 115.37, Thunderbird 152, and Thunderbird 140.12.

Affected products

• Mozilla Firefox: before 115.37.0 (fixed in 115.37.0); before 152.0.0 (fixed in 152.0.0); from 128.0, before 140.12.0 (fixed in 140.12.0)
• Mozilla Thunderbird: before 140.12.0 (fixed in 140.12.0); before 152.0.0 (fixed in 152.0.0)

Published 2026-06-16. Last modified 2026-07-15.