CVE-2026-100787: Mozilla Firefox

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

Sandbox escape in the XUL component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 153.4, and Firefox 157.

Affected products

• Mozilla Firefox: before 153.4.0 (fixed in 153.4.0); from 154.0.0, before 157.0.0 (fixed in 157.0.0)
• Mozilla Thunderbird: before 153.4.0 (fixed in 153.4.0); from 154.0, before 157.0 (fixed in 157.0)

Published 2026-09-29. Last modified 2026-10-05.