CVE-2026-8959

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 3.1

9.6CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

EPSS

0.4% chance of exploitation in the next 30 days; higher than 35% of CVEs (scores of 2026-10-25)

CWEs

CWE-20, CWE-119, CWE-693

Published

2026-05-19

Modified

2026-10-14

Record from

the NVD, synced 2026-10-19

Affected

• mozilla:firefox
• mozilla:thunderbird

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2034754
• https://www.mozilla.org/security/advisories/mfsa2026-46/
• https://www.mozilla.org/security/advisories/mfsa2026-48/
• https://www.mozilla.org/security/advisories/mfsa2026-50/
• https://www.mozilla.org/security/advisories/mfsa2026-51/

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