CVE-2026-12299: Mozilla Firefox

Medium severity, CVSS 5.4. EPSS: 0.3% chance of exploitation in the next 30 days.

JIT miscompilation in the DOM: Core & HTML 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 (fixed in 152.0); from 140.0, before 140.12.0 (fixed in 140.12.0)
• Mozilla Thunderbird: before 152.0.0 (fixed in 152.0.0); from 140.0, before 140.12.0 (fixed in 140.12.0)

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