CVE-2026-0878: Mozilla Firefox

High severity, CVSS 8.0. EPSS: 0.5% chance of exploitation in the next 30 days.

Sandbox escape due to incorrect boundary conditions in the Graphics: CanvasWebGL component. This vulnerability was fixed in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

Affected products

• Mozilla Firefox: before 140.7.0 (fixed in 140.7.0); before 147.0 (fixed in 147.0)
• Mozilla Thunderbird: before 140.7.0 (fixed in 140.7.0); before 147.0 (fixed in 147.0)

Published 2026-01-13. Last modified 2026-07-15.