CVE-2026-20856 json
Windows Server Update Service (WSUS) Remote Code Execution Vulnerability
published 2026-01-13 9 mo ago modified 2026-07-30 3 mo ago also EUVD-2026-2163
- cvss
- 8.1
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 1.1%
- EPSS 1.1% chance of exploitation in 30 days, percentile 66%
- public exploits
- 0
- none known
Summary
Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
Patch / fix
- Microsoft Windows 10 Version 1607 10.0.14393.8783
- Microsoft Windows 10 Version 1809 10.0.17763.8276
- Microsoft Windows 10 Version 21H2 10.0.19044.6809
- Microsoft Windows 10 Version 22H2 10.0.19045.6809
- Microsoft Windows 11 version 23H2 10.0.22631.6491
- Microsoft Windows 11 Version 24H2 10.0.26100.7623
- Microsoft Windows 11 Version 25H2 10.0.26200.7623
- Microsoft Windows Server 2012 6.2.9200.25868
- Microsoft Windows Server 2012 (Server Core installation) 6.2.9200.25868
- Microsoft Windows Server 2012 R2 6.3.9600.22968
- Microsoft Windows Server 2012 R2 (Server Core installation) 6.3.9600.22968
- Microsoft Windows Server 2016 10.0.14393.8783
- Microsoft Windows Server 2016 (Server Core installation) 10.0.14393.8783
- Microsoft Windows Server 2019 10.0.17763.8276
- Microsoft Windows Server 2019 (Server Core installation) 10.0.17763.8276
- Microsoft Windows Server 2022 10.0.20348.4648
- Microsoft Windows Server 2022, 23H2 Edition (Server Core installation) 10.0.25398.2092
- Microsoft Windows Server 2025 10.0.26100.32230
- Microsoft Windows Server 2025 (Server Core installation) 10.0.26100.32230
CISA SSVC
- Exploitation
- none
- Automatable
- no
- Technical impact
- total
- Assessed
- 9 mo ago
Exploit prediction
1.12% chance of exploitation in the next 30 days, higher than 66% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 3.1 | 8.1 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C |
| CNA | 3.1 | 8.1 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H |
Affected products
- Microsoft Windows 10 Version 1607
- Microsoft Windows 10 Version 1809
- Microsoft Windows 10 Version 21H2
- Microsoft Windows 10 Version 22H2
- Microsoft Windows 11 version 23H2
- Microsoft Windows 11 Version 24H2
- Microsoft Windows 11 Version 25H2
- Microsoft Windows Server 2012
- Microsoft Windows Server 2012 (Server Core installation)
- Microsoft Windows Server 2012 R2
- Microsoft Windows Server 2012 R2 (Server Core installation)
- Microsoft Windows Server 2016
- Microsoft Windows Server 2016 (Server Core installation)
- Microsoft Windows Server 2019
- Microsoft Windows Server 2019 (Server Core installation)
- Microsoft Windows Server 2022
- Microsoft Windows Server 2022, 23H2 Edition (Server Core installation)
- Microsoft Windows Server 2025
- Microsoft Windows Server 2025 (Server Core installation)
Classification
- Weakness
-
- CWE-20 Improper Input Validation
References
-
msrc.microsoft.com
/update-guide/vulnerability/CVE-2026-20856
vendor-advisory, patch
Sources
- CVE List CVE-2026-20856
- NVD CVE-2026-20856
Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.