Vulnerability in Mozilla Firefox
CVE-2025-5263
Error handling for script execution was incorrectly isolated from web content, which could have allowed cross-origin leak attacks. This vulnerability was fixed in Firefox 139, Firefox ESR 115.24, Firefox ESR 128.11, Thunderbird 139, and Thunderbird 128.11.
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: 0.002 (14.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 14th percentile — 14.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000
Affected products
- Mozilla Firefox — versions 115.24, 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/mfsa2025-43/ (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-2025-5263?
- CVE-2025-5263 is a medium-severity vulnerability in Mozilla Firefox, classified under Origin Validation Error. CVSS score: 4.3/10. Published 2025-05-27.
- How severe is CVE-2025-5263?
- Medium severity. CVSS v3 base score is 4.3 out of 10.
- Is CVE-2025-5263 known to be exploited?
- 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.