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Windows 10 1607 CVE-2026-20856

HIGH
Improper Input Validation (CWE-20)
2026-01-13 secure@microsoft.com
Authentication Bypass Microsoft Windows 10 1607 Windows 10 1809 Windows 10 21h2 Windows 10 22h2 Windows 11 23h2 Windows 11 24h2 Windows 11 25h2 Windows Server 2012 Windows Server 2016 Windows Server 2019 Windows Server 2022 Windows Server 2022 23h2 Windows Server 2025
8.1
CVSS 3.1 · Vendor: microsoft
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Severity by source

Vendor (microsoft) PRIMARY
8.1 HIGH
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from Vendor (microsoft) · only source for this CVE.

CVSS VectorVendor: microsoft

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

Lifecycle Timeline

2
Analysis Generated
Mar 12, 2026 - 21:54 vuln.today
CVE Published
Jan 13, 2026 - 18:16 nvd
HIGH 8.1

DescriptionCVE.org

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

AnalysisAI

Remote code execution in Windows Server Update Service affects Windows 11 25h2, Windows Server 2025, 2022, and 2016 due to inadequate input validation, enabling unauthenticated network-based attackers to execute arbitrary code with high impact. The vulnerability requires specific conditions to exploit (high complexity) but carries significant risk across widely-deployed server infrastructure with no patch currently available.

Technical ContextAI

Classified as CWE-20 (Improper Input Validation). Affects the Windows Server Update component of Windows 10 1607. Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.

RemediationAI

Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.

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Same weakness CWE-20 – Improper Input Validation

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Same technique Authentication Bypass

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CVE-2026-20856 vulnerability details – vuln.today
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