Microsoft Security Response CenterCVE-2026-56181

Windows Network Address Translation (NAT) Spoofing Vulnerability

Origin validation error in Windows Network Address Translation (NAT) allows an unauthorized attacker to perform spoofing over an adjacent network.

Read the vendor bulletin Get alerts for Windows Server 2025 (Server Core installation)

8.3CVSS out of 10Medium severity

Scope

What the vendor says is affected

Windows Server 2025 (Server Core installation)
Windows 11 Version 25H2 for ARM64-based Systems
Windows 11 Version 25H2 for x64-based Systems
Windows 11 Version 24H2 for ARM64-based Systems
Windows 11 Version 24H2 for x64-based Systems
Windows Server 2025
Windows 11 version 26H1 for x64-based Systems
Windows 11 Version 26H1 for ARM64-based Systems

Versions the vendor lists as fixed

10.0.26100.33158
10.0.26200.8875
10.0.26100.8875
10.0.28000.2525

Next step

What the vendor recommends

The mitigation is disabled by default. To enable it, apply the following registry key and reboot the machine. reg add HKLM\SYSTEM\CurrentControlSet\Services\Winnat /v DisableFailOver /t REG_DWORD /d 1 /f Install KB5099536. Install KB5101650. Install KB5101649.

Review the complete instructions on the vendor's site

Timeline

When this advisory changed

Jul 14, 2026 at 7:00 AM UTC
Published by Microsoft Security Response Center
The publication date reported by the vendor.
Sep 28, 2026 at 11:20 AM UTC
Added to SecurityAlert
We collected the advisory from the official source.

Vulnerabilities

CVEs named in this advisory

CVE-2026-56181View CVSS, KEV, EPSS, and threat context

Source

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Vendor: Microsoft Security Response Center
Advisory ID: CVE-2026-56181
Last source check: Sep 28, 2026 at 11:20 AM UTC

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Your environment

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Watch Windows Server 2025 (Server Core installation)

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What the vendor says is affected

Versions the vendor lists as fixed

What the vendor recommends

When this advisory changed

CVEs named in this advisory

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