# CVE-2026-40405: Windows TCP/IP Denial of Service Vulnerability

CVE-2026-40405 is fixed in 8 products on 1 platform, first by KB5089549, released May 12, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-40405
- Priority: High
- CVSS: 7.5 (Important)
- EPSS: 0.0108
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Vendor exploitability assessment: Exploitation Less Likely
- Published: May 12, 2026
- Weakness: NULL Pointer Dereference
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40405

## Description

<p>Null pointer dereference in Windows TCP/IP allows an unauthorized attacker to deny service over a network.</p>

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Microsoft | Windows 11 Version 24H2 for ARM64-based Systems |  | [KB5089549](https://patchblox.com/security/data/fix/microsoft/kb5089549.md) | May 12, 2026 |
| Microsoft | Windows 11 Version 24H2 for ARM64-based Systems |  | [KB5089466](https://patchblox.com/security/data/fix/microsoft/kb5089466.md) | May 12, 2026 |
| Microsoft | Windows 11 Version 24H2 for x64-based Systems |  | [KB5089549](https://patchblox.com/security/data/fix/microsoft/kb5089549.md) | May 12, 2026 |
| Microsoft | Windows 11 Version 24H2 for x64-based Systems |  | [KB5089466](https://patchblox.com/security/data/fix/microsoft/kb5089466.md) | May 12, 2026 |
| Microsoft | Windows 11 Version 25H2 for ARM64-based Systems |  | [KB5089549](https://patchblox.com/security/data/fix/microsoft/kb5089549.md) | May 12, 2026 |
| Microsoft | Windows 11 Version 25H2 for ARM64-based Systems |  | [KB5089466](https://patchblox.com/security/data/fix/microsoft/kb5089466.md) | May 12, 2026 |
| Microsoft | Windows 11 Version 25H2 for x64-based Systems |  | [KB5089549](https://patchblox.com/security/data/fix/microsoft/kb5089549.md) | May 12, 2026 |
| Microsoft | Windows 11 Version 25H2 for x64-based Systems |  | [KB5089466](https://patchblox.com/security/data/fix/microsoft/kb5089466.md) | May 12, 2026 |
| Microsoft | Windows 11 Version 26H1 for ARM64-based Systems | 28000.2113 | [KB5089548](https://patchblox.com/security/data/fix/microsoft/kb5089548.md) | May 12, 2026 |
| Microsoft | Windows 11 version 26H1 for x64-based Systems | 28000.2113 | [KB5089548](https://patchblox.com/security/data/fix/microsoft/kb5089548.md) | May 12, 2026 |
| Microsoft | Windows Server 2025 | 26100.32860 | [KB5087539](https://patchblox.com/security/data/fix/microsoft/kb5087539.md) | May 12, 2026 |
| Microsoft | Windows Server 2025 | 26100.32772 | [KB5087423](https://patchblox.com/security/data/fix/microsoft/kb5087423.md) | May 12, 2026 |
| Microsoft | Windows Server 2025 (Server Core installation) | 26100.32860 | [KB5087539](https://patchblox.com/security/data/fix/microsoft/kb5087539.md) | May 12, 2026 |
| Microsoft | Windows Server 2025 (Server Core installation) | 26100.32772 | [KB5087423](https://patchblox.com/security/data/fix/microsoft/kb5087423.md) | May 12, 2026 |

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Data as of 2026-11-08T06:59:42Z 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

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