What is CVE-2025-6427?

CVE-2025-6427 is a critical-severity vulnerability in Mozilla Firefox, classified under Protection Mechanism Failure. CVSS score: 9.1/10. Published 2025-06-24.

How severe is CVE-2025-6427?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Vulnerability in Mozilla Firefox

CVE-2025-6427

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.

EPSS: 0.003 (22.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

Affected products

Mozilla Firefox — versions 140
Mozilla Thunderbird — versions 140

Weakness classification (CWE)

CWE-693 — Protection Mechanism Failure

References

security@mozilla.org (Permissions Required)
security@mozilla.org (Vendor Advisory)
security@mozilla.org

Frequently asked questions

What is CVE-2025-6427?: CVE-2025-6427 is a critical-severity vulnerability in Mozilla Firefox, classified under Protection Mechanism Failure. CVSS score: 9.1/10. Published 2025-06-24.
How severe is CVE-2025-6427?: Critical severity. CVSS v3 base score is 9.1 out of 10.