Out-of-bounds read in Firefox ESR - CVE-2026-8959
Published: May 19, 2026
Vulnerability identifier: #VU131844
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-8959
CWE-ID: CWE-125
Exploitation vector: Local access
Exploit availability:
No public exploit available
Vendor: Mozilla
Affected software:
Firefox ESR
Firefox ESR
Detailed vulnerability description
The vulnerability allows a local user to escape the sandbox.
The vulnerability exists due to incorrect boundary conditions in the Widget: Win32 component when handling local interaction with the application. A local user can trigger the flaw to escape the sandbox.
The issue affects the Win32-specific component.
How to mitigate CVE-2026-8959
Install security update from vendor's website.