Vulnerability in Mozilla Firefox
CVE-2025-5271
Previewing a response in Devtools ignored CSP headers, which could have allowed content injection attacks. This vulnerability was fixed in Firefox 139 and Thunderbird 139.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (21.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 21st percentile — 21.0% 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: 0.003 · change: 0.000
Affected products
- Mozilla Firefox — versions 139
- Mozilla Thunderbird — versions 139
Weakness classification (CWE)
References
- bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
- www.mozilla.org/security/advisories/mfsa2025-42/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2025-45/
Frequently asked questions
- What is CVE-2025-5271?
- CVE-2025-5271 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Encoding or Escaping of Output. CVSS score: 6.5/10. Published 2025-05-27.
- How severe is CVE-2025-5271?
- Medium severity. CVSS v3 base score is 6.5 out of 10.