Vulnerability in Mozilla Firefox
CVE-2026-4702
JIT miscompilation in the JavaScript Engine component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.007 (50.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 50th percentile — 50.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.007 · change: +0.002
Affected products
- Mozilla Firefox — versions 140.9, 149
- Mozilla Thunderbird — versions 140.9, 149
Weakness classification (CWE)
References
- bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
- www.mozilla.org/security/advisories/mfsa2026-20/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-22/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-23/
- www.mozilla.org/security/advisories/mfsa2026-24/
Frequently asked questions
- What is CVE-2026-4702?
- CVE-2026-4702 is a critical-severity vulnerability in Mozilla Firefox, classified under Access of Resource Using Incompatible Type (Type Confusion). CVSS score: 9.8/10. Published 2026-03-24.
- How severe is CVE-2026-4702?
- Critical severity. CVSS v3 base score is 9.8 out of 10.