Summary
Impact: Remote Code Execution. Microsoft rating: Important. Not known to be exploited — Exploitation Less Likely. Customer action: Required.
Details
According to the CVSS metric, the attack complexity is high (AC:H). What does that mean for this vulnerability?
The attacker must inject themselves into the logical network path between the target and the resource requested by the victim to read or modify network communications. This is called a machine-in-the-middle (MITM) attack.
Security updates
10.0.17763.8276 — https://support.microsoft.com/help/5073723
10.0.20348.4648 — https://support.microsoft.com/help/5073457
10.0.19044.6809 — https://support.microsoft.com/help/5073724
10.0.26100.32230 — https://support.microsoft.com/en-us/topic/a6021fd2-b3b7-45a7-b68e-35c28a2a77da
10.0.26200.7623 — https://support.microsoft.com/help/5074109
10.0.22631.6491 — https://support.microsoft.com/help/5073455
10.0.25398.2092 — https://support.microsoft.com/help/5073450
10.0.14393.8783 — https://support.microsoft.com/help/5073722
6.2.9200.25868 — https://support.microsoft.com/help/5073698
6.3.9600.22968 — https://support.microsoft.com/help/5073696
Vulnerabilities 1
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High 8.1
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.
Revision history
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#2
Updated acknowledgment. This is an informational change only.
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#1
Information published.
References
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CVE-2026-20856 Windows Server Update Service (WSUS) Remote Code Execution Vulnerability - HTML
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20856
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Microsoft Exploitability Index
https://www.microsoft.com/en-us/msrc/exploitability-index?rtc=1
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Microsoft Support Lifecycle
https://support.microsoft.com/lifecycle
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Common Vulnerability Scoring System
https://www.first.org/cvss