CVE-2026-8959

EUVD-2026-30910
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.
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTPrimary
9.6 CRITICAL
NETWORK
LOW
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Base Score
CVSS 3.x
EPSS Score
Percentile: Unknown
Affected Products (NVD)
VendorProductVersion
mozillafirefox_esr
𝑥
< 140.11.0
mozillafirefox
𝑥
< 151.0.0
mozillathunderbird_esr
𝑥
< 140.11
mozillathunderbird
𝑥
< 151.0.0
𝑥
= Vulnerable software versions
Debian logo
Debian Releases
Debian Product
Codename
firefox
sid
151.0-1
fixed
firefox-esr
bookworm
140.10.2esr-1~deb12u1
fixed
bookworm (security)
140.10.2esr-1~deb12u1
fixed
bullseye
115.14.0esr-1~deb11u1
fixed
bullseye (security)
140.10.2esr-1~deb11u1
fixed
forky
140.10.2esr-1
fixed
sid
140.11.0esr-1
fixed
trixie
140.10.2esr-1~deb13u1
fixed
trixie (security)
140.10.2esr-1~deb13u1
fixed
thunderbird
bookworm
1:140.10.1esr-1~deb12u1
fixed
bookworm (security)
1:140.10.2esr-1~deb12u1
fixed
bullseye
1:115.12.0-1~deb11u1
fixed
bullseye (security)
1:140.10.2esr-1~deb11u1
fixed
forky
1:140.10.2esr-1
fixed
sid
1:140.10.2esr-1
fixed
trixie
1:140.10.1esr-1~deb13u1
fixed
trixie (security)
1:140.10.2esr-1~deb13u1
fixed
Common Weakness Enumeration
Vulnerability Media Exposure
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/