Origin validation error in Windows and Windows Server - CVE-2026-56181
Published: July 17, 2026
Vulnerability identifier: #VU138167
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:A/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-56181
CWE-ID: CWE-346
Exploitation vector: Adjecent network
Exploit availability:
No public exploit available
Vendor: Microsoft
Affected software:
Windows
Windows Server
Windows
Windows Server
Detailed vulnerability description
The vulnerability allows a remote attacker to perform spoofing.
The vulnerability exists due to an origin validation error in Windows Network Address Translation (NAT) when handling network traffic on an adjacent network. A remote attacker can position themselves on a logically adjacent network path to perform spoofing.
Exploitation requires machine-in-the-middle conditions on a logically adjacent topology.
How to mitigate CVE-2026-56181
Install security update from vendor's website.