CVE-2026-8959

CRITICAL

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

Title source: cna
STIX 2.1

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.

References (5)

Core 5

Scores

CVSS v3 9.6
EPSS 0.0008
EPSS Percentile 24.1%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

CISA SSVC

Vulnrichment
Exploitation none
Automatable no
Technical Impact total

Details

CWE
CWE-119 CWE-20 CWE-693
Status published
Products (8)
mozilla/firefox < 140.11.0
mozilla/firefox < 151.0.0
Mozilla/Firefox 140.11 - 140.*
Mozilla/Firefox 151
mozilla/thunderbird < 140.11
mozilla/thunderbird < 151.0.0
Mozilla/Thunderbird 140.11 - 140.*
Mozilla/Thunderbird 151
Published May 19, 2026
Tracked Since May 19, 2026