CVE-2025-6427

Name: CVE-2025-6427
Creator: NVD / NIST
Published: 2025-06-24T13:15:23.65+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.1/10EPSS 0.30%

Last modified Jun 17, 2026

CVE-2025-6427 is a critical-severity vulnerability rated 9.1/10 on the CVSS scale. 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. EPSS estimates a 0.30% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.1/10

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

EPSS Probability

0.30%

21.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-693

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 140.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1966927Permissions Required
https://www.mozilla.org/security/advisories/mfsa2025-51/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2025-54/

Timeline

Published: Jun 24, 2025
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2025-6427?

How severe is CVE-2025-6427?

CVE-2025-6427 has a CVSS score of 9.1/10 (CRITICAL severity). The EPSS model estimates a 0.30% probability of exploitation in the next 30 days.

How do I fix CVE-2025-6427?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2025-6427?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST