Heap-based buffer overflow in Microsoft Windows and Windows Server - CVE-2025-21418

Vulnerability identifier: #VU103780

CSH Severity: High

CVSS v4: 8.5 [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]

CVE-ID: CVE-2025-21418

CWE-ID: CWE-122

Exploitation vector: Local access

Exploit availability: The vulnerability is being exploited in the wild

The vulnerability allows a local user to escalate privileges on the system.

The vulnerability exists due to a boundary error in ancillary function driver for WinSock. A local user can trigger a heap-based buffer overflow and execute arbitrary code with elevated privileges.

Note, the vulnerability is being actively exploited in the wild.

Microsoft Windows
Windows Server

Install updates from vendor's website.

Microsoft Windows - addressed in versions 10 21H2 10.0.19044.5487, 10 22H2 10.0.19045.5487, 10 1507 10.0.10240.20915, 10 1607 10.0.14393.7785, 10 1809 10.0.17763.6893, 11 22H2 10.0.22621.4890, 11 23H2 10.0.22631.4890, 11 24H2 10.0.26100.3107
Windows Server - addressed in versions 2008 R2 6.1.7601.27566, 2008 6.0.6003.23117, 2012 R2 6.3.9600.22417, 2012 6.2.9200.25317, 2016 10.0.14393.7785, 2022 23H2 10.0.25398.1425, 2022 10.0.20348.3148, 2022 10.0.20348.3207, 2025 10.0.26100.3107, 2025 10.0.26100.3194

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2025-21418

• Privilege escalation in Microsoft Windows ancillary function driver for WinSock