by Kastro
Paper/Archive/CVE-2026-8959

CVE-2026-8959

Mozilla Firefox — Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component

EPSS 0.4%CVSS 9.6
critical.is priorityof 100
36
CVSS 9.6 (ADP)9.6 / 10 × 3028.8Not in CISA KEV+300.0EPSS percentile 36.0.360 × 207.2No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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.

Affected

ProductAffectedFixed inSource
Firefoxsee advisory140.11CNA
Thunderbirdsee advisory140.11CNA

Scores by source

CISA ADP9.6CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
CISA ADPSSVCExploitation: none · Automatable: no · Technical impact: total

References

refbugzilla.mozilla.org/show_bug.cgi?id=2034754refmozilla.org/security/advisories/mfsa2026-46refmozilla.org/security/advisories/mfsa2026-48refmozilla.org/security/advisories/mfsa2026-50refmozilla.org/security/advisories/mfsa2026-51