CVE-2026-100804: Mozilla Firefox

Critical severity, CVSS 9.6. EPSS: 0.3% chance of exploitation in the next 30 days.

Sandbox escape due to use-after-free in the Preferences: Backend component. This vulnerability was fixed in Thunderbird 157 and Firefox 157.

Affected products

• Mozilla Firefox
• Mozilla Thunderbird

Published 2026-09-29. Last modified 2026-09-30.