CVE-2025-6427

critical

Description

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.

References

https://www.mozilla.org/security/advisories/mfsa2025-54/

https://www.mozilla.org/security/advisories/mfsa2025-51/

https://bugzilla.mozilla.org/show_bug.cgi?id=1966927

Details

Source: Mitre, NVD

Published: 2025-06-24

Updated: 2026-04-13

Risk Information

CVSS v2

Base Score: 9.4

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:N

Severity: High

CVSS v3

Base Score: 9.1

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Severity: Critical

EPSS

EPSS: 0.00018