CVE-2026-8959

  1. OpenCVE
  2. Vulnerabilities (CVE)
  3. 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.

9.6 /10

CVSS v3 : CRITICAL

V3 Legend

Vector :

Exploitability : 2.8 / Impact : 6.0

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact HIGH

Integrity Impact HIGH

Availability Impact HIGH

Scope CHANGED

References
Link Resource
https://bugzilla.mozilla.org/show_bug.cgi?id=2034754 Permissions 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
Configurations

Configuration 1 (hide)

OR cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
History

20 May 2026, 14:28

Type Values Removed Values Added
CPE cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:*
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:*
First Time Mozilla thunderbird
Mozilla
Mozilla firefox
References () https://bugzilla.mozilla.org/show_bug.cgi?id=2034754 - () https://bugzilla.mozilla.org/show_bug.cgi?id=2034754 - Permissions Required
References () https://www.mozilla.org/security/advisories/mfsa2026-46/ - () https://www.mozilla.org/security/advisories/mfsa2026-46/ - Vendor Advisory
References () https://www.mozilla.org/security/advisories/mfsa2026-48/ - () https://www.mozilla.org/security/advisories/mfsa2026-48/ - Vendor Advisory
References () https://www.mozilla.org/security/advisories/mfsa2026-50/ - () https://www.mozilla.org/security/advisories/mfsa2026-50/ - Vendor Advisory
References () https://www.mozilla.org/security/advisories/mfsa2026-51/ - () https://www.mozilla.org/security/advisories/mfsa2026-51/ - Vendor Advisory

19 May 2026, 18:16

Type Values Removed Values Added
References
  • () https://www.mozilla.org/security/advisories/mfsa2026-50/ -
  • () https://www.mozilla.org/security/advisories/mfsa2026-51/ -
Summary (en) Sandbox escape due to incorrect boundary conditions in the Widget: Win32 component. This vulnerability was fixed in Firefox 151 and Firefox ESR 140.11. (en) 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.

19 May 2026, 17:16

Type Values Removed Values Added
CVSS v2 : unknown
v3 : unknown 		v2 : unknown
v3 : 9.6
CWE CWE-693
CWE-119
CWE-20

19 May 2026, 14:16

Type Values Removed Values Added
New CVE
Information

Published : 2026-05-19 14:16

Updated : 2026-05-20 14:28

NVD link : CVE-2026-8959

Mitre link : CVE-2026-8959

CVE.ORG link : CVE-2026-8959

JSON object : View

Products Affected

mozilla

  • firefox
  • thunderbird
CWE
CWE-20

Improper Input Validation

CWE-119

Improper Restriction of Operations within the Bounds of a Memory Buffer

CWE-693

Protection Mechanism Failure