CVE-2026-4692: Mozilla Firefox

Critical severity, CVSS 10.0. EPSS: 0.5% chance of exploitation in the next 30 days.

Sandbox escape in the Responsive Design Mode component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.

Affected products

• Mozilla Firefox: before 115.34.0 (fixed in 115.34.0); before 149.0 (fixed in 149.0); from 128.0, before 140.9.0 (fixed in 140.9.0)
• Mozilla Thunderbird: before 140.9.0 (fixed in 140.9.0); before 149.0 (fixed in 149.0)

Published 2026-03-24. Last modified 2026-07-15.