Instituto Nacional de ciberseguridad. Sección Incibe
Instituto Nacional de Ciberseguridad. Sección INCIBE-CERT

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CVE-2026-8959

Severity CVSS v4.0:
Pending analysis
Type:
CWE-20 Input Validation
Publication date:
19/05/2026
Last modified:
20/05/2026

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.

Impact

Vector 3.x
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H CVSS v3.1 Severity and Metrics:

Base Score: 9.60 CRITICAL
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): Required
Scope (S): Changed
Confidentiality (C): High
Integrity (I): High
Availability (A): High

Base Score 3.x
9.60
Severity 3.x
CRITICAL

Vulnerable products and versions

CPE From Up to
cpe:2.3:a:mozilla:firefox:*:*:*:*:esr:*:*:* 140.11.0 (excluding)
cpe:2.3:a:mozilla:firefox:*:*:*:*:-:*:*:* 151.0.0 (excluding)
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:esr:*:*:* 140.11 (excluding)
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* 151.0.0 (excluding)

To consult the complete list of CPE names with products and versions, see this page


References to Advisories, Solutions, and Tools