Vulnerability Description
Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.
CVSS Score
9.6
CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Mozilla | Firefox | < 140.11.0 |
| Mozilla | Thunderbird | < 140.11 |
Related Weaknesses (CWE)
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2034754Permissions Required
- https://www.mozilla.org/security/advisories/mfsa2026-46/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-48/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-50/Vendor Advisory
- https://www.mozilla.org/security/advisories/mfsa2026-51/Vendor Advisory
FAQ
What is CVE-2026-8959?
CVE-2026-8959 is a vulnerability with a CVSS score of 9.6 (CRITICAL). Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151, Firefox ESR 140.11, Thunderbird 151, and Thunderbird 140.11.
How severe is CVE-2026-8959?
CVE-2026-8959 has been rated CRITICAL with a CVSS base score of 9.6/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-8959?
Check the references section above for vendor advisories and patch information. Affected products include: Mozilla Firefox, Mozilla Thunderbird.