CVE-2011-2991: Mozilla Firefox

High severity, CVSS 10.0. EPSS: 4.5% chance of exploitation in the next 30 days.

The browser engine in Mozilla Firefox 4.x through 5, SeaMonkey 2.x before 2.3, Thunderbird before 6, and possibly other products does not properly implement JavaScript, which allows remote attackers to cause a denial of service (memory corruption and application crash) or possibly execute arbitrary code via unspecified vectors.

Affected products

• Mozilla Firefox: version 4.0 only; version 4.0.1 only; version 5.0 only
• Mozilla Seamonkey: version 2.0 only; version 2.0.1 only; version 2.0.2 only; version 2.0.3 only; version 2.0.4 only; version 2.0.5 only; …
• Mozilla Thunderbird: up to and including 5.0; version 0.1 only; version 0.2 only; version 0.3 only; version 0.4 only; version 0.5 only; …

Published 2011-08-18. Last modified 2026-06-16.