CVE-2025-6427: Mozilla Firefox

Critical severity, CVSS 9.1. EPSS: 0.4% chance of exploitation in the next 30 days.

An attacker was able to bypass the `connect-src` directive of a Content Security Policy by manipulating subdocuments. This would have also hidden the connections from the Network tab in Devtools. This vulnerability was fixed in Firefox 140 and Thunderbird 140.

Affected products

• Mozilla Firefox: before 140.0 (fixed in 140.0)

Published 2025-06-24. Last modified 2026-09-30.