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.
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.004 (28.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 28th percentile — 28.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.000
Affected products
- Mozilla Firefox — versions 140
- Mozilla Thunderbird — versions 140
Weakness classification (CWE)
References
- bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
- www.mozilla.org/security/advisories/mfsa2025-51/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2025-54/
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.