CVE-2026-0877: Mozilla Firefox

High severity, CVSS 8.1. EPSS: 0.5% chance of exploitation in the next 30 days.

Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 147, Firefox ESR 115.32, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

Affected products

• Mozilla Firefox: before 115.32.0 (fixed in 115.32.0); before 147.0 (fixed in 147.0); from 128.0, before 140.7.0 (fixed in 140.7.0)
• 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.