Jan 2026: Windows Server Update Service (WSUS) Remote Code Execution Vulnerability
CVE-2026-20856 Published on January 13, 2026

Windows Server Update Service (WSUS) Remote Code Execution Vulnerability
Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.

Vendor Advisory NVD

Weakness Type

Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

Products Associated with CVE-2026-20856

You can be notified by email with stack.watch whenever vulnerabilities like CVE-2026-20856 are published in these products:

Microsoft Windows 10

Microsoft Windows Server 2019

Microsoft Windows Server 2022

Microsoft Windows Server 2025

Microsoft Windows 11 25h2

Microsoft Windows 11 23h2

Microsoft Windows Server 23h2

Microsoft Windows 11 24h2

Microsoft Windows Server 2016

Microsoft Windows Server 2012

Microsoft Windows Server 2012 R2

Affected Versions

Microsoft Windows 10 Version 1607:

Version 10.0.14393.0 and below 10.0.14393.8783 is affected.

Microsoft Windows 10 Version 1809:

Version 10.0.17763.0 and below 10.0.17763.8276 is affected.

Microsoft Windows 10 Version 21H2:

Version 10.0.19044.0 and below 10.0.19044.6809 is affected.

Microsoft Windows 10 Version 22H2:

Version 10.0.19045.0 and below 10.0.19045.6809 is affected.

Microsoft Windows 11 version 22H3:

Version 10.0.22631.0 and below 10.0.22631.6491 is affected.

Microsoft Windows 11 Version 23H2:

Version 10.0.22631.0 and below 10.0.22631.6491 is affected.

Microsoft Windows 11 Version 24H2:

Version 10.0.26100.0 and below 10.0.26100.7623 is affected.

Microsoft Windows 11 Version 25H2:

Version 10.0.26200.0 and below 10.0.26200.7623 is affected.

Microsoft Windows Server 2012:

Version 6.2.9200.0 and below 6.2.9200.25868 is affected.

Microsoft Windows Server 2012 (Server Core installation):

Version 6.2.9200.0 and below 6.2.9200.25868 is affected.

Microsoft Windows Server 2012 R2:

Version 6.3.9600.0 and below 6.3.9600.22968 is affected.

Microsoft Windows Server 2012 R2 (Server Core installation):

Version 6.3.9600.0 and below 6.3.9600.22968 is affected.

Microsoft Windows Server 2016:

Version 10.0.14393.0 and below 10.0.14393.8783 is affected.

Microsoft Windows Server 2016 (Server Core installation):

Version 10.0.14393.0 and below 10.0.14393.8783 is affected.

Microsoft Windows Server 2019:

Version 10.0.17763.0 and below 10.0.17763.8276 is affected.

Microsoft Windows Server 2019 (Server Core installation):

Version 10.0.17763.0 and below 10.0.17763.8276 is affected.

Microsoft Windows Server 2022:

Version 10.0.20348.0 and below 10.0.20348.4648 is affected.

Microsoft Windows Server 2022, 23H2 Edition (Server Core installation):

Version 10.0.25398.0 and below 10.0.25398.2092 is affected.

Microsoft Windows Server 2025:

Version 10.0.26100.0 and below 10.0.26100.32230 is affected.

Microsoft Windows Server 2025 (Server Core installation):

Version 10.0.26100.0 and below 10.0.26100.32230 is affected.

Exploit Probability

EPSS

0.15%

Percentile

35.20%