Information disclosure in Mozilla Firefox
CVE-2025-5266
Script elements loading cross-origin resources generated load and error events which leaked information enabling XS-Leaks attacks. This vulnerability was fixed in Firefox 139, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11.
Vulnerability class: Information Disclosure
Published · last modified .
CVSS v3 metric
CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N.
EPSS exploit prediction
EPSS: 0.003 (23.5th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 23rd percentile — 23.5% 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 128.11, 139
- Mozilla Thunderbird — versions 128.11, 139
Weakness classification (CWE)
Public proof-of-concept exploits
References
- bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
- www.mozilla.org/security/advisories/mfsa2025-42/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2025-44/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2025-45/
- www.mozilla.org/security/advisories/mfsa2025-46/
- af854a3a-2127-422b-91ae-364da2661108
- af854a3a-2127-422b-91ae-364da2661108
Frequently asked questions
- What is CVE-2025-5266?
- CVE-2025-5266 is a medium-severity vulnerability in Mozilla Firefox, classified under Information Disclosure. CVSS score: 4.3/10. Published 2025-05-27.
- How severe is CVE-2025-5266?
- Medium severity. CVSS v3 base score is 4.3 out of 10.
- Is CVE-2025-5266 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.