# CVE-2026-20856: Windows Server Update Service (WSUS) Remote Code Execution Vulnerability CVE-2026-20856 is fixed in 29 products on 1 platform, first by KB5073722, released January 13, 2026. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2026-20856 - Priority: High - CVSS: 8.1 (Important) - EPSS: 0.0112 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Vendor exploitability assessment: Exploitation Less Likely - Published: Jan 13, 2026 - Weakness: Improper Input Validation - Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-20856 ## Description

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

## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Microsoft | Windows 10 Version 1607 for 32-bit Systems | 14393.8783 | [KB5073722](https://patchblox.com/security/data/fix/microsoft/kb5073722.md) | Jan 13, 2026 | | Microsoft | Windows 10 Version 1607 for x64-based Systems | 14393.8783 | [KB5073722](https://patchblox.com/security/data/fix/microsoft/kb5073722.md) | Jan 13, 2026 | | Microsoft | Windows 10 Version 1809 for 32-bit Systems | 17763.8276 | [KB5073723](https://patchblox.com/security/data/fix/microsoft/kb5073723.md) | Jan 13, 2026 | | Microsoft | Windows 10 Version 1809 for x64-based Systems | 17763.8276 | [KB5073723](https://patchblox.com/security/data/fix/microsoft/kb5073723.md) | Jan 13, 2026 | | Microsoft | Windows 10 Version 21H2 for 32-bit Systems | | [KB5073724](https://patchblox.com/security/data/fix/microsoft/kb5073724.md) | Jan 13, 2026 | | Microsoft | Windows 10 Version 21H2 for ARM64-based Systems | | [KB5073724](https://patchblox.com/security/data/fix/microsoft/kb5073724.md) | Jan 13, 2026 | | Microsoft | Windows 10 Version 21H2 for x64-based Systems | | [KB5073724](https://patchblox.com/security/data/fix/microsoft/kb5073724.md) | Jan 13, 2026 | | Microsoft | Windows 10 Version 22H2 for 32-bit Systems | | [KB5073724](https://patchblox.com/security/data/fix/microsoft/kb5073724.md) | Jan 13, 2026 | | Microsoft | Windows 10 Version 22H2 for ARM64-based Systems | | [KB5073724](https://patchblox.com/security/data/fix/microsoft/kb5073724.md) | Jan 13, 2026 | | Microsoft | Windows 10 Version 22H2 for x64-based Systems | | [KB5073724](https://patchblox.com/security/data/fix/microsoft/kb5073724.md) | Jan 13, 2026 | | Microsoft | Windows 11 Version 23H2 for ARM64-based Systems | 22631.6491 | [KB5073455](https://patchblox.com/security/data/fix/microsoft/kb5073455.md) | Jan 13, 2026 | | Microsoft | Windows 11 Version 23H2 for x64-based Systems | 22631.6491 | [KB5073455](https://patchblox.com/security/data/fix/microsoft/kb5073455.md) | Jan 13, 2026 | | Microsoft | Windows 11 Version 24H2 for ARM64-based Systems | | [KB5074109](https://patchblox.com/security/data/fix/microsoft/kb5074109.md) | Jan 13, 2026 | | Microsoft | Windows 11 Version 24H2 for x64-based Systems | | [KB5074109](https://patchblox.com/security/data/fix/microsoft/kb5074109.md) | Jan 13, 2026 | | Microsoft | Windows 11 Version 25H2 for ARM64-based Systems | | [KB5074109](https://patchblox.com/security/data/fix/microsoft/kb5074109.md) | Jan 13, 2026 | | Microsoft | Windows 11 Version 25H2 for x64-based Systems | | [KB5074109](https://patchblox.com/security/data/fix/microsoft/kb5074109.md) | Jan 13, 2026 | | Microsoft | Windows Server 2012 | | [KB5073698](https://patchblox.com/security/data/fix/microsoft/kb5073698.md) | Jan 13, 2026 | | Microsoft | Windows Server 2012 (Server Core installation) | | [KB5073698](https://patchblox.com/security/data/fix/microsoft/kb5073698.md) | Jan 13, 2026 | | Microsoft | Windows Server 2012 R2 | | [KB5073696](https://patchblox.com/security/data/fix/microsoft/kb5073696.md) | Jan 13, 2026 | | Microsoft | Windows Server 2012 R2 (Server Core installation) | | [KB5073696](https://patchblox.com/security/data/fix/microsoft/kb5073696.md) | Jan 13, 2026 | | Microsoft | Windows Server 2016 | 14393.8783 | [KB5073722](https://patchblox.com/security/data/fix/microsoft/kb5073722.md) | Jan 13, 2026 | | Microsoft | Windows Server 2016 (Server Core installation) | 14393.8783 | [KB5073722](https://patchblox.com/security/data/fix/microsoft/kb5073722.md) | Jan 13, 2026 | | Microsoft | Windows Server 2019 | 17763.8276 | [KB5073723](https://patchblox.com/security/data/fix/microsoft/kb5073723.md) | Jan 13, 2026 | | Microsoft | Windows Server 2019 (Server Core installation) | 17763.8276 | [KB5073723](https://patchblox.com/security/data/fix/microsoft/kb5073723.md) | Jan 13, 2026 | | Microsoft | Windows Server 2022 | 20348.4648 | [KB5073457](https://patchblox.com/security/data/fix/microsoft/kb5073457.md) | Jan 13, 2026 | | Microsoft | Windows Server 2022 (Server Core installation) | 20348.4648 | [KB5073457](https://patchblox.com/security/data/fix/microsoft/kb5073457.md) | Jan 13, 2026 | | Microsoft | Windows Server 2022, 23H2 Edition (Server Core installation) | 25398.2092 | [KB5073450](https://patchblox.com/security/data/fix/microsoft/kb5073450.md) | Jan 13, 2026 | | Microsoft | Windows Server 2025 | 26100.32230 | [KB5073379](https://patchblox.com/security/data/fix/microsoft/kb5073379.md) | Jan 13, 2026 | | Microsoft | Windows Server 2025 (Server Core installation) | 26100.32230 | [KB5073379](https://patchblox.com/security/data/fix/microsoft/kb5073379.md) | Jan 13, 2026 | --- Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.