CVE-2021-29986: Mozilla Firefox

High severity, CVSS 8.1. EPSS: 1.3% chance of exploitation in the next 30 days.

A suspected race condition when calling getaddrinfo led to memory corruption and a potentially exploitable crash. *Note: This issue only affected Linux operating systems. Other operating systems are unaffected.* This vulnerability affects Thunderbird < 78.13, Thunderbird < 91, Firefox ESR < 78.13, and Firefox < 91.

Affected products

• Mozilla Firefox: before 91.0 (fixed in 91.0)
• Mozilla Firefox ESR: before 78.13.0 (fixed in 78.13.0)
• Mozilla Thunderbird: before 78.13.0 (fixed in 78.13.0)

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