Windows Server Update Service (WSUS) Remote Code Execution Vulnerability
This high-severity Microsoft Server advisory covers CVE-2026-20856 affecting Windows Server 2012 (Server Core installation), Windows Server 2012 R2 (Server Core installation), Windows Server 2016 (Server Core installation).
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Summary
Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
Affected products named by the advisory: Windows Server 2012; Windows Server 2012 (Server Core installation); Windows Server 2012 R2; Windows Server 2012 R2 (Server Core installation); and 8 more.
Affected products named by the advisory: Windows Server 2016 (Server Core installation); Windows Server 2019 (Server Core installation); Windows Server 2022, 23H2 Edition (Server Core installation); Windows Server 2025 (Server Core installation).
- Windows 10 Version 1607 10.0.14393.0 before 10.0.14393.8783
- Windows 10 Version 1809 10.0.17763.0 before 10.0.17763.8276
- Windows 10 Version 21H2 10.0.19044.0 before 10.0.19044.6809
- Windows 10 Version 22H2 10.0.19045.0 before 10.0.19045.6809
- Windows 11 version 23H2 10.0.22631.0 before 10.0.22631.6491
- Windows 11 Version 23H2 10.0.22631.0 before 10.0.22631.6491
- Windows 11 Version 24H2 10.0.26100.0 before 10.0.26100.7623
- Windows 11 Version 25H2 10.0.26200.0 before 10.0.26200.7623
- Windows Server 2012 6.2.9200.0 before 6.2.9200.25868
- Windows Server 2012 (Server Core installation) 6.2.9200.0 before 6.2.9200.25868
- Windows Server 2012 R2 6.3.9600.0 before 6.3.9600.22968
- Windows Server 2012 R2 (Server Core installation) 6.3.9600.0 before 6.3.9600.22968
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
- 10.0.14393.8783
- 10.0.17763.8276
- 10.0.19044.6809
- 10.0.19045.6809
- 10.0.22631.6491
- 10.0.26100.7623
- 10.0.26200.7623
- 6.2.9200.25868
- 6.3.9600.22968
- 10.0.20348.4648
- 10.0.25398.2092
- 10.0.26100.32230
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
Mitigation checklist
- Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
Official advisory · high-confidence parse· fetched 2 hours ago·verify at source
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