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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Send malformed WSUS protocol request
  2. Exploit
    Bypass input validation checks
  3. Execution
    Trigger remote code execution
  4. Impact
    Execute arbitrary commands as SYSTEM

Vulnerability Assessment

Weakness
CWE
CWE-20
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V2 - Validation and Business Logic Input validation, allowlisting
Exploitation Conditions

Windows Server Update Service must be exposed to network access. Attacker requires ability to craft specific malformed WSUS protocol packets. No authentication required. Attack complexity is high due to specific payload construction requirements.
Impact

CVSS 8.1 (HIGH). Attack vector: Network. Complexity: High. Privileges required: None. User interaction: None. Exploitation no authentication required. Exploitable via remote/network.
Exploit ScenarioDerived

A remote attacker without authentication could exploit this vulnerability to compromise the affected system.
This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).
Patch available 0.1% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

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.

Earlier versions of this analysis (1)
v1 Mar 12, 2026 - 21:54 CVSS 8.1

Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network. [CVSS 8.1 HIGH]

RemediationAI

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

Affected Packages

microsoft windows_10_version_1607_10_0_14393_8783 fix: Windows 10 Version 1607 for 32-bit Systems 10.0.14393.8783, Windows 10 Version 1607 for x64-based Systems 10.0.14393.8783
microsoft windows_10_version_1809_10_0_17763_8276 fix: Windows 10 Version 1809 for 32-bit Systems 10.0.17763.8276, Windows 10 Version 1809 for x64-based Systems 10.0.17763.8276
microsoft windows_10_version_21h2_10_0_19044_6809 fix: Windows 10 Version 21H2 for 32-bit Systems 10.0.19044.6809, Windows 10 Version 21H2 for ARM64-based Systems 10.0.19044.6809, Windows 10 Version 21H2 for x64-based Systems 10.0.19044.6809
microsoft windows_10_version_22h2_10_0_19045_6809 fix: Windows 10 Version 22H2 for 32-bit Systems 10.0.19045.6809, Windows 10 Version 22H2 for ARM64-based Systems 10.0.19045.6809, Windows 10 Version 22H2 for x64-based Systems 10.0.19045.6809
microsoft windows_11_version_23h2_10_0_22631_6491 fix: Windows 11 Version 23H2 for ARM64-based Systems 10.0.22631.6491, Windows 11 Version 23H2 for x64-based Systems 10.0.22631.6491
microsoft windows_11_version_24h2_10_0_26100_7623 fix: Windows 11 Version 24H2 for ARM64-based Systems 10.0.26100.7623, Windows 11 Version 24H2 for x64-based Systems 10.0.26100.7623
microsoft windows_11_version_25h2_10_0_26200_7623 fix: Windows 11 Version 25H2 for ARM64-based Systems 10.0.26200.7623, Windows 11 Version 25H2 for x64-based Systems 10.0.26200.7623
microsoft windows_server_2012_6_2_9200_25868 fix: Windows Server 2012 6.2.9200.25868, Windows Server 2012 (Server Core installation) 6.2.9200.25868
microsoft windows_server_2012_r2_6_3_9600_22968 fix: Windows Server 2012 R2 6.3.9600.22968, Windows Server 2012 R2 (Server Core installation) 6.3.9600.22968
microsoft windows_server_2016_10_0_14393_8783 fix: Windows Server 2016 10.0.14393.8783, Windows Server 2016 (Server Core installation) 10.0.14393.8783
microsoft windows_server_2019_10_0_17763_8276 fix: Windows Server 2019 10.0.17763.8276, Windows Server 2019 (Server Core installation) 10.0.17763.8276
microsoft windows_server_2022_10_0_20348_4648 fix: Windows Server 2022 10.0.20348.4648, Windows Server 2022 (Server Core installation) 10.0.20348.4648
microsoft windows_server_2022_23h2_edition_10_0_25398_2092 fix: Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.2092
microsoft windows_server_2025_10_0_26100_32230 fix: Windows Server 2025 10.0.26100.32230, Windows Server 2025 (Server Core installation) 10.0.26100.32230

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 14 packages in microsoft

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Technical ContextAI · show details

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.

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  • Exploit and PoC references, threat intelligence from 22 sources
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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

DescriptionCVE.org

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

Executive ViewAI

Why It Matters

Organizations using Improper input validation in Windows Server Update Service face notable risk from CVE-2026-20856, a input validation vulnerability rated CVSS 8.1. Successful exploitation could significantly impact the confidentiality, integrity, or availability of affected systems. Organizations should apply vendor updates when available and consider compensating controls in the interim.

Business Impact: High
Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Implement network-level access controls to limit exposure; (2) Enable enhanced monitoring and alerting; (3) Apply principle of least privilege.

Threat Intelligence Overview

EPSS Score
0.1%
Top 65% exploitable
Data Quality
3 sources
Confidence: Low
NVD CVE.org EPSS VulDB

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity HIGH
CISA KEV No
Public POC No
EPSS 0.1%
Patch available Yes
Active threat No
Deciding rule
HIGH severity (CVSS 7.0-8.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
No
Human Impact
High

Priority Score

40
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +40
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Authentication Bypass CRITICAL

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

Affected Products (CPE)CVE.org

cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x86:*
cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x64:*
cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:x86:*
cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_11_23h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_11_25h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2012:-:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2012:r2:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2016:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2019:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2022:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2022_23h2:*:*:*:*:*:*:*:*
cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:*

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Same weakness CWE-20 – Improper Input Validation

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CVE-2009-0927 HIGH POC
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CVE-2019-0604 CRITICAL POC
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Same technique Authentication Bypass

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CVE-2012-4681 CRITICAL POC
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CVE-2013-2465 CRITICAL POC
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CVE-2011-3544 CRITICAL POC
9.8
CVE-2022-40684 CRITICAL POC
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CVE-2024-0012 CRITICAL POC
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References

Advisories & patches
ADVISORY https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20856 ADVISORY https://vuldb.com/vuln/340786

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