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
EPSS: 0.001 (20.0th percentile) — read the EPSS interpretation.
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.
Affected products
- Mozilla Firefox — versions 140.11, 151
- Mozilla Thunderbird — versions 140.11, 151
Weakness classification (CWE)
References
- security@mozilla.org (Permissions Required)
- security@mozilla.org (Vendor Advisory)
- security@mozilla.org (Vendor Advisory)
- security@mozilla.org (Vendor Advisory)
- security@mozilla.org (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.