CVE-2009-0777: Mozilla Firefox

Medium severity, CVSS 5.8. EPSS: 1.5% chance of exploitation in the next 30 days.

Mozilla Firefox before 3.0.7, Thunderbird before 2.0.0.21, and SeaMonkey before 1.1.15 decode invisible characters when they are displayed in the location bar, which causes an incorrect address to be displayed and makes it easier for remote attackers to spoof URLs and conduct phishing attacks.

Affected products

• Mozilla Firefox: up to and including 3.0.6; version 1.0 only; version 1.0.1 only; version 1.0.2 only; version 1.0.3 only; version 1.0.4 only; …
• Mozilla Seamonkey: up to and including 1.1.14; version 1.0 only; version 1.0.1 only; version 1.0.2 only; version 1.0.3 only; version 1.0.5 only; …
• Mozilla Thunderbird: up to and including 2.0.0.20; version 2.0.0.0 only; version 2.0.0.4 only; version 2.0.0.5 only; version 2.0.0.6 only; version 2.0.0.9 only; …

Published 2009-03-05. Last modified 2026-06-16.