CVE-2026-100831: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 0.3% chance of exploitation in the next 30 days.

Use-after-free in the DOM: UI Events & Focus Handling component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 153.4, and Firefox 157.

Affected products

• Mozilla Firefox
• Mozilla Thunderbird

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