Integer overflow in Mozilla Firefox
CVE-2026-8949
Integer overflow in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.
Vulnerability class: Integer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.006 (46.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 47th percentile — 46.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: +0.000
Affected products
- Mozilla Firefox — versions 140.11, 151
- Mozilla Thunderbird — versions 140.11, 151
Weakness classification (CWE)
References
- bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
- www.mozilla.org/security/advisories/mfsa2026-46/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-48/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-50/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-51/ (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-8949?
- CVE-2026-8949 is a high-severity vulnerability in Mozilla Firefox, classified under Integer Overflow or Wraparound. CVSS score: 7.5/10. Published 2026-05-19.
- How severe is CVE-2026-8949?
- High severity. CVSS v3 base score is 7.5 out of 10.