CVE-2026-100820: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 0.2% chance of exploitation in the next 30 days.

Privilege escalation in the Address Bar component. This vulnerability was fixed in Firefox ESR 153.4, Thunderbird 157, Thunderbird 140.17, Thunderbird 153.4, Firefox 157, and Firefox ESR 140.17.

Affected products

• Mozilla Firefox: before 140.17.0 (fixed in 140.17.0); from 141.0, 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 140.17.0 (fixed in 140.17.0); from 141.0, 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.