CVE-2021-4127: Mozilla Firefox ESR

Critical severity, CVSS 9.8. EPSS: 0.9% chance of exploitation in the next 30 days.

An out of date graphics library (Angle) likely contained vulnerabilities that could potentially be exploited. This vulnerability affects Thunderbird < 78.9 and Firefox ESR < 78.9.

Affected products

• Mozilla Firefox ESR: before 78.9.0 (fixed in 78.9.0)
• Mozilla Thunderbird: before 78.9.0 (fixed in 78.9.0)

Published 2022-12-22. Last modified 2026-06-17.