CVE-2023-6209: Debian Linux

Medium severity, CVSS 6.5. EPSS: 1.4% chance of exploitation in the next 30 days.

Relative URLs starting with three slashes were incorrectly parsed, and a path-traversal "/../" part in the path could be used to override the specified host. This could contribute to security problems in web sites. This vulnerability affects Firefox < 120, Firefox ESR < 115.5.0, and Thunderbird < 115.5.

Affected products

• Debian Debian Linux: version 10.0 only; version 11.0 only; version 12.0 only
• Mozilla Firefox: before 120.0 (fixed in 120.0)
• Mozilla Firefox ESR: before 115.5.0 (fixed in 115.5.0)
• Mozilla Thunderbird: before 115.5 (fixed in 115.5)

Published 2023-11-21. Last modified 2026-06-17.