Integer overflow in Mozilla Firefox
CVE-2026-8956
Integer overflow in the Networking: JAR 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 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: 0.006 (48.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 49th percentile — 48.6% 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-2026-8956?
- CVE-2026-8956 is a critical-severity vulnerability in Mozilla Firefox, classified under Integer Overflow or Wraparound. CVSS score: 9.8/10. Published 2026-05-19.
- How severe is CVE-2026-8956?
- Critical severity. CVSS v3 base score is 9.8 out of 10.