CVE-2026-20856
published 2026-01-13CVE-2026-20856: Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
PriorityP353high8.1CVSS 3.1
AVNACHPRNUINSUCHIHAH
EPSS
1.07%
61.0th percentile
Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
Affected
41 ranges· showing 25
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| microsoft | windows_10_1607 | < 10.0.14393.8783 | 10.0.14393.8783 |
| microsoft | windows_10_1809 | < 10.0.17763.8276 | 10.0.17763.8276 |
| microsoft | windows_10_21h2 | < 10.0.19044.6809 | 10.0.19044.6809 |
| microsoft | windows_10_22h2 | < 10.0.19045.6809 | 10.0.19045.6809 |
| microsoft | windows_10_version_1607 | >= 10.0.14393.0 < 10.0.14393.8783 | 10.0.14393.8783 |
| microsoft | windows_10_version_1809 | >= 10.0.17763.0 < 10.0.17763.8276 | 10.0.17763.8276 |
| microsoft | windows_10_version_21h2 | >= 10.0.19044.0 < 10.0.19044.6809 | 10.0.19044.6809 |
| microsoft | windows_10_version_22h2 | >= 10.0.19045.0 < 10.0.19045.6809 | 10.0.19045.6809 |
| microsoft | windows_11_23h2 | < 10.0.22631.6491 | 10.0.22631.6491 |
| microsoft | windows_11_24h2 | < 10.0.26100.7623 | 10.0.26100.7623 |
| microsoft | windows_11_25h2 | < 10.0.26200.7623 | 10.0.26200.7623 |
| microsoft | windows_11_version_22h3 | >= 10.0.22631.0 < 10.0.22631.6491 | 10.0.22631.6491 |
| microsoft | windows_11_version_23h2 | >= 10.0.22631.0 < 10.0.22631.6491 | 10.0.22631.6491 |
| microsoft | windows_11_version_24h2 | >= 10.0.26100.0 < 10.0.26100.7623 | 10.0.26100.7623 |
| microsoft | windows_11_version_25h2 | >= 10.0.26200.0 < 10.0.26200.7623 | 10.0.26200.7623 |
| microsoft | windows_server_2012 | — | — |
| microsoft | windows_server_2012 | >= 6.2.9200.0 < 6.2.9200.25868 | 6.2.9200.25868 |
| microsoft | windows_server_2012_r2 | >= 6.3.9600.0 < 6.3.9600.22968 | 6.3.9600.22968 |
| microsoft | windows_server_2016 | < 10.0.14393.8783 | 10.0.14393.8783 |
| microsoft | windows_server_2016 | >= 10.0.14393.0 < 10.0.14393.8783 | 10.0.14393.8783 |
| microsoft | windows_server_2019 | < 10.0.17763.8276 | 10.0.17763.8276 |
| microsoft | windows_server_2019 | >= 10.0.17763.0 < 10.0.17763.8276 | 10.0.17763.8276 |
| microsoft | windows_server_2022 | < 10.0.20348.4648 | 10.0.20348.4648 |
| microsoft | windows_server_2022 | >= 10.0.20348.0 < 10.0.20348.4648 | 10.0.20348.4648 |
| microsoft | windows_server_2022_23h2 | < 10.0.25398.2092 | 10.0.25398.2092 |
CVSS provenance
nvdv3.18.1HIGHCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
vendor_msrc8.1HIGH
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Microsoft
Windows Server Update Service (WSUS) Remote Code Execution Vulnerability
vendor_msrc·2026-01-13·CVSS 8.1
CVE-2026-20856 [HIGH] CWE-20 Windows Server Update Service (WSUS) Remote Code Execution Vulnerability
Windows Server Update Service (WSUS) Remote Code Execution Vulnerability
Description: Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
FAQ: 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.
Windows Server Update Service: Windows Server Update Service
Microsoft: Microsoft
Customer Action Required: Yes
Impact: Remote Code Execution
Exploit Status: Publicly Disclosed:No;Exploited:No;Latest Software Release:Exploitation Less Likely
Re
GHSA
GHSA-gmj5-vp5f-rx2g: Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network
ghsa_unreviewed·2026-01-13
CVE-2026-20856 [HIGH] CWE-20 GHSA-gmj5-vp5f-rx2g: Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network
Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
No detection rules found.
No public exploits indexed.
Qualys
Microsoft and Adobe Patch Tuesday, January 2026 Security Update Review
blogs_qualys·2026-01-13
Microsoft and Adobe Patch Tuesday, January 2026 Security Update Review
## Table of Contents
Microsoft Patch Tuesday forJanuary2026
Adobe Patches for January 2026
Zero-day Vulnerabilities Patched inJanuaryPatch Tuesday Edition
Critical Severity Vulnerabilities Patched inJanuaryPatch Tuesday Edition
Other Microsoft Vulnerability Highlights
Microsoft Release Summary
Discover and Prioritize Vulnerabilities inVulnerability Management, Detection & Response (VMDR)
Rapid Response with TruRisk Eliminate
EVALUATE Vendor-Suggested Mitigation withPolicy Audit(PA)
Qualys Monthly Webinar Series
Starting the year on a security-first note, Microsoft’s January 2026 Patch Tuesday resolves several vulnerabilities that could impact enterprise environments. Here’s a quick breakdown of what you need to know.
## Microsoft Patch Tuesday for January 2026
This month’s rel
Bleepingcomputer
Microsoft January 2026 Patch Tuesday fixes 3 zero-days, 114 flaws
blogs_bleepingcomputer·2026-01-13·CVSS 5.5
[MEDIUM] Microsoft January 2026 Patch Tuesday fixes 3 zero-days, 114 flaws
## Microsoft January 2026 Patch Tuesday fixes 3 zero-days, 114 flaws
## Lawrence Abrams
57 Elevation of Privilege vulnerabilities
3 Security Feature Bypass vulnerabilities
22 Remote Code Execution vulnerabilities
22 Information Disclosure vulnerabilities
2 Denial of Service vulnerabilities
5 Spoofing vulnerabilities
When BleepingComputer reports on Patch Tuesday security updates, we only count those released by Microsoft today. Therefore, the number of flaws does not include Microsoft Edge (1 flaw) and Mariner vulnerabilities fixed earlier this month.
To learn more about the non-security updates released today, you can review our dedicated articles on the Windows 11 KB5074109 & KB5073455 cumulative updates and Windows 10 KB5073724 extended security update .
## 3 zero-days, one ex
Qualys
Microsoft and Adobe Patch Tuesday, January 2026 Security Update Review | Qualys
blogs_qualys·2026-01-13
Microsoft and Adobe Patch Tuesday, January 2026 Security Update Review | Qualys
#### Table of Contents
- Microsoft Patch Tuesday forJanuary2026
- Adobe Patches for January 2026
- Zero-day Vulnerabilities Patched inJanuaryPatch Tuesday Edition
- Critical Severity Vulnerabilities Patched inJanuaryPatch Tuesday Edition
- Other Microsoft Vulnerability Highlights
- Microsoft Release Summary
- Discover and Prioritize Vulnerabilities inVulnerability Management, Detection & Response (VMDR)
- Rapid Response with TruRisk Eliminate
- EVALUATE Vendor-Suggested Mitigation withPolicy Audit(PA)
- Qualys Monthly Webinar Series
Starting the year on a security-first note, Microsoft’s January 2026 Patch Tuesday resolves several vulnerabilities that could impact enterprise environments. Here’s a quick breakdown of what you need to know.
## Microsoft Patch Tuesday for January 2026
Thi
Wiz
CVE-2026-20856 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 8.1
CVE-2026-20856 [HIGH] CVE-2026-20856 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-20856 :
vulnerability analysis and mitigation
Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
Source : NVD
## 8.1
Score
Published January 13, 2026
Severity HIGH
CNA Score 8.1
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 31.9
Exploitation Probability (EPSS) 0.1
Sources
NVD
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2026-01-13
Published