Use-after-free in Microsoft Windows and Windows Server - CVE-2026-21241

Vulnerability identifier: #VU122558

CSH Severity: Low

CVSS v4: 7.3 [CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-21241

CWE-ID: CWE-416

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a local user to compromise vulnerable system.

The vulnerability exists due to a use-after-free error in Windows Ancillary Function Driver for WinSock. A local user can gain elevated privileges on the target system.

Microsoft Windows
Windows Server

Install updates from vendor's website.

Microsoft Windows - addressed in versions 11 23H2 10.0.22631.6649, 11 24H2 10.0.26100.7781, 11 24H2 10.0.26100.7840, 11 26H1 10.0.28000.1575
Windows Server - addressed in versions 2012 R2 6.3.9600.23022, 2022 23H2 10.0.25398.2149, 2022 10.0.20348.4711, 2022 10.0.20348.4773, 2025 10.0.26100.32313, 2025 10.0.26100.32370

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21241

• Multiple vulnerabilities in Microsoft Windows Ancillary Function Driver for WinSock