CVE-2009-3376: Mozilla Firefox

High severity, CVSS 9.3. EPSS: 3.2% chance of exploitation in the next 30 days.

Mozilla Firefox before 3.0.15 and 3.5.x before 3.5.4, and SeaMonkey before 2.0, does not properly handle a right-to-left override (aka RLO or U+202E) Unicode character in a download filename, which allows remote attackers to spoof file extensions via a crafted filename, as demonstrated by displaying a non-executable extension for an executable file.

Affected products

• Mozilla Firefox: version 3.0 only; version 3.0.1 only; version 3.0.2 only; version 3.0.3 only; version 3.0.4 only; version 3.0.5 only; …
• Mozilla Seamonkey: up to and including 1.5.0.10; version 1.0 only; version 1.0.1 only; version 1.0.2 only; version 1.0.3 only; version 1.0.4 only; …

Published 2009-10-29. Last modified 2026-06-16.