Vulnerability in Mozilla Firefox
CVE-2026-12304
Same-origin policy bypass in the Networking: Cookies component. This vulnerability was fixed in Firefox 152, Firefox ESR 140.12, Thunderbird 152, and Thunderbird 140.12.
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: 0.002 (7.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 8th percentile — 7.7% 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 140.12, 152
- Mozilla Thunderbird — versions 140.12, 152
Weakness classification (CWE)
References
- bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
- www.mozilla.org/security/advisories/mfsa2026-57/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-58/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-60/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-61/ (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-12304?
- CVE-2026-12304 is a critical-severity vulnerability in Mozilla Firefox, classified under Origin Validation Error. CVSS score: 9.1/10. Published 2026-06-16.
- How severe is CVE-2026-12304?
- Critical severity. CVSS v3 base score is 9.1 out of 10.