CVE-2026-20856:

Critical vulnerability in Windows Server Update Service allows remote code execution.

Score
A numerical rating that indicates how dangerous this vulnerability is.

8.1High

Published Date:Jan 13, 2026
CISA KEV Date:*No Data*
Industries Affected:20

Threat Predictions

EPSS Score:0.1
EPSS Percentile:35%

Exploitability

Score:2.2
Attack Vector:NETWORK
Attack Complexity:HIGH
Privileges Required:NONE
User Interaction:NONE
Scope:UNCHANGED

Impact

Score:5.9
Confidentiality Impact:HIGH
Integrity Impact:HIGH
Availability Impact:HIGH

Description Preview

Critical vulnerability in Windows Server Update Service allows remote code execution.

Overview

This vulnerability in Windows Server Update Service presents a significant security risk due to its potential for remote code execution without user interaction. With a CVSS v3.1 base score of 8.1 (High), it requires no privileges and can be exploited over the network, though the attack complexity is high. The impact on confidentiality, integrity, and availability is severe, potentially allowing attackers to gain full control of affected systems. The weakness is categorized as CWE-20, indicating improper input validation as the root cause.

Remediation

To mitigate this vulnerability, system administrators should immediately apply the latest security updates provided by Microsoft for Windows Server Update Service. Additionally, it is recommended to implement network segmentation, restrict access to WSUS servers, and monitor for suspicious activities. Regular security audits and penetration testing should be conducted to identify and address potential vulnerabilities in the update infrastructure. Organizations should also consider implementing additional security measures such as intrusion detection systems and endpoint protection to enhance overall security posture.