CVE-2026-20856

HighCVSS 8.1/10Last modified Jul 30, 2026

Description

Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.

Metrics

CVSS 3.1 8.1/10CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Weakness enumeration

CWE-20

Affected software

Vendor	Product	Versions
Microsoft	Windows 10 Version 1607	>= 10.0.14393.0, < 10.0.14393.8783
Microsoft	Windows 10 Version 1809	>= 10.0.17763.0, < 10.0.17763.8276
Microsoft	Windows 10 Version 21H2	>= 10.0.19044.0, < 10.0.19044.6809
Microsoft	Windows 10 Version 22H2	>= 10.0.19045.0, < 10.0.19045.6809
Microsoft	Windows 11 version 23H2	>= 10.0.22631.0, < 10.0.22631.6491
Microsoft	Windows 11 Version 23H2	>= 10.0.22631.0, < 10.0.22631.6491
Microsoft	Windows 11 Version 24H2	>= 10.0.26100.0, < 10.0.26100.7623
Microsoft	Windows 11 Version 25H2	>= 10.0.26200.0, < 10.0.26200.7623
Microsoft	Windows Server 2012	>= 6.2.9200.0, < 6.2.9200.25868
Microsoft	Windows Server 2012 (Server Core installation)	>= 6.2.9200.0, < 6.2.9200.25868
Microsoft	Windows Server 2012 R2	>= 6.3.9600.0, < 6.3.9600.22968
Microsoft	Windows Server 2012 R2 (Server Core installation)	>= 6.3.9600.0, < 6.3.9600.22968
Microsoft	Windows Server 2016	>= 10.0.14393.0, < 10.0.14393.8783
Microsoft	Windows Server 2016 (Server Core installation)	>= 10.0.14393.0, < 10.0.14393.8783
Microsoft	Windows Server 2019	>= 10.0.17763.0, < 10.0.17763.8276
Microsoft	Windows Server 2019 (Server Core installation)	>= 10.0.17763.0, < 10.0.17763.8276
Microsoft	Windows Server 2022	>= 10.0.20348.0, < 10.0.20348.4648
Microsoft	Windows Server 2022, 23H2 Edition (Server Core installation)	>= 10.0.25398.0, < 10.0.25398.2092
Microsoft	Windows Server 2025	>= 10.0.26100.0, < 10.0.26100.32230
Microsoft	Windows Server 2025 (Server Core installation)	>= 10.0.26100.0, < 10.0.26100.32230

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20856Vendor Advisory

Timeline

Published: Jan 13, 2026
Last modified: Jul 30, 2026
NVD status: Analyzed

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