Heap-based buffer overflow in Microsoft Windows and Windows Server - CVE-2026-21244

Vulnerability identifier: #VU122570

CSH Severity: Medium

CVSS v4: 7 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-21244

CWE-ID: CWE-122

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to execute arbitrary code on the target system.

The vulnerability exists due to a boundary error in Windows Hyper-V. A remote user can trick a victim to load a specially crafted file, trigger a heap-based buffer overflow and execute arbitrary code on the target system.

Successful exploitation of this vulnerability may result in complete compromise of vulnerable system.

Microsoft Windows
Windows Server

Install updates from vendor's website.

Microsoft Windows - addressed in versions 10 21H2 10.0.19044.6937, 10 22H2 10.0.19045.6937, 10 1607 10.0.14393.8868, 10 1809 10.0.17763.8389, 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, 2016 10.0.14393.8868, 2019 10.0.17763.8389, 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-2026-21244

• Multiple vulnerabilities in Microsoft Windows Hyper-V