#VU121387 Input validation error in Windows and Windows Server - CVE-2026-20856

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Main Vulnerability Database Vulnerabilities #VU121387

#VU121387 Input validation error in Windows and Windows Server - CVE-2026-20856

Published: January 14, 2026


Vulnerability identifier: #VU121387
Vulnerability risk: High
CVSSv4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2026-20856
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability: No public exploit available
Vulnerable software:
Windows
Windows Server
Software vendor:
Microsoft

Description

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

The vulnerability exists due to insufficient validation of user-supplied input in Windows Server Update Service (WSUS). A remote attacker can perform a man-in-the-middle (MitM) attack and execute arbitrary code on the system.


Remediation

Install updates from vendor's website.

External links