CVE-2021-29970: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 1.4% chance of exploitation in the next 30 days.

A malicious webpage could have triggered a use-after-free, memory corruption, and a potentially exploitable crash. *This bug could only be triggered when accessibility was enabled.*. This vulnerability affects Thunderbird < 78.12, Firefox ESR < 78.12, and Firefox < 90.

Affected products

• Mozilla Firefox: before 90.0 (fixed in 90.0)
• Mozilla Firefox ESR: before 78.12 (fixed in 78.12)
• Mozilla Thunderbird: before 78.12 (fixed in 78.12)

Published 2021-08-05. Last modified 2026-06-17.