CVE-2024-9398: Mozilla Firefox

Medium severity, CVSS 5.3. EPSS: 0.6% chance of exploitation in the next 30 days.

By checking the result of calls to `window.open` with specifically set protocol handlers, an attacker could determine if the application which implements that protocol handler is installed. This vulnerability affects Firefox < 131, Firefox ESR < 128.3, Thunderbird < 128.3, and Thunderbird < 131.

Affected products

• Mozilla Firefox: before 128.3.0 (fixed in 128.3.0); before 131.0 (fixed in 131.0)
• Mozilla Thunderbird: before 128.3 (fixed in 128.3); version 129.0 only

Published 2024-10-01. Last modified 2026-10-08.