CVE-2026-56179: Windows Network Address Translation (NAT) Spoofing Vulnerability

Overview

Severity

High (CVSS 8.3)

CVSS Vector

CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C

Category

Spoofing

Exploit Status

Not Exploited

Exploitation Likelihood

Less Likely

Patch Tuesday

2026-Aug

Released

2026-08-11

Description

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

Affected Products (8)

Windows

• 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

Security Updates (5)

• 5120233
• 5120228
• 5121003
• 5120994
• 5121000

Acknowledgments

Malcolm Stagg with <a href="https://www.sodium24.com/">SODIUM-24, LLC</a>

Revision History

• 2026-08-11: Information published.