CVE-2026-8959

critical

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.

References

https://www.mozilla.org/security/advisories/mfsa2026-51/

https://www.mozilla.org/security/advisories/mfsa2026-50/

https://www.mozilla.org/security/advisories/mfsa2026-48/

https://www.mozilla.org/security/advisories/mfsa2026-46/

https://bugzilla.mozilla.org/show_bug.cgi?id=2034754

Details

Source: Mitre, NVD

Published: 2026-05-19

Updated: 2026-05-20

Risk Information

CVSS v2

Base Score: 10

Vector: CVSS2#AV:N/AC:L/Au:N/C:C/I:C/A:C

Severity: Critical

CVSS v3

Base Score: 9.6

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H