CVE-2026-20856
High
Description
Improper input validation in Windows Server Update Service allows an unauthorized attacker to execute code over a network.
SeverityHigh
CVSS8.1
Exploit probability—
Product
Microsoft Windows
PublishedJan 13, 2026
First seenJan 13, 2026
Weakness typeCWE-20Improper input validation
How to fix
Update
- microsoft windows_10_160710.0.14393.8783 or later
- microsoft windows_10_180910.0.17763.8276 or later
- microsoft windows_10_21h210.0.19044.6809 or later
- microsoft windows_10_22h210.0.19045.6809 or later
- microsoft windows_11_23h210.0.22631.6491 or later
- microsoft windows_11_24h210.0.26100.7623 or later
- microsoft windows_11_25h210.0.26200.7623 or later
- microsoft windows_server_201610.0.14393.8783 or later
- microsoft windows_server_201910.0.17763.8276 or later
- microsoft windows_server_202210.0.20348.4648 or later
- microsoft windows_server_2022_23h210.0.25398.2092 or later
- microsoft windows_server_202510.0.26100.32230 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| microsoft windows_10_1607 | v < 10.0.14393.8783 | 10.0.14393.8783 |
| microsoft windows_10_1809 | v < 10.0.17763.8276 | 10.0.17763.8276 |
| microsoft windows_10_21h2 | v < 10.0.19044.6809 | 10.0.19044.6809 |
| microsoft windows_10_22h2 | v < 10.0.19045.6809 | 10.0.19045.6809 |
| microsoft windows_11_23h2 | v < 10.0.22631.6491 | 10.0.22631.6491 |
| microsoft windows_11_24h2 | v < 10.0.26100.7623 | 10.0.26100.7623 |
| microsoft windows_11_25h2 | v < 10.0.26200.7623 | 10.0.26200.7623 |
| microsoft windows_server_2012 | No range specified, r2 | — |
| microsoft windows_server_2016 | v < 10.0.14393.8783 | 10.0.14393.8783 |
| microsoft windows_server_2019 | v < 10.0.17763.8276 | 10.0.17763.8276 |
| microsoft windows_server_2022 | v < 10.0.20348.4648 | 10.0.20348.4648 |
| microsoft windows_server_2022_23h2 | v < 10.0.25398.2092 | 10.0.25398.2092 |
| microsoft windows_server_2025 | v < 10.0.26100.32230 | 10.0.26100.32230 |
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