CVE-2026-56181 — Windows Network Address Translation (NAT) Spoofing Vulnerability

Executive Summary

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

Overview

8.3

CVSS HIGH

Moderate

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Spoofing

Weakness CWE-346: Origin Validation Error

Released Jul 14 2026

Last Updated Jul 14 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00237 — 0.1484 percentile

NVD CVSS 8.3 HIGH — matches MSRC

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

ATTACK VECTOR

Adjacent_network

ATTACK COMPLEXITY

High

PRIVILEGES REQUIRED

None

USER INTERACTION

None

SCOPE

Changed

CONFIDENTIALITY

High

INTEGRITY

High

AVAILABILITY

High

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 7.2

EPSS Score

0.00237

probability of exploitation in the next 30 days

0.1484 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

8 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 11 Version 24H2 for ARM64-based Systems	`5101650 (Security Update)`	Moderate	Spoofing	Yes
Windows 11 Version 24H2 for x64-based Systems	`5101650 (Security Update)`	Moderate	Spoofing	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5101650 (Security Update)`	Moderate	Spoofing	Yes
Windows 11 Version 25H2 for x64-based Systems	`5101650 (Security Update)`	Moderate	Spoofing	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5101649 (Security Update)`	Moderate	Spoofing	Yes
Windows 11 version 26H1 for x64-based Systems	`5101649 (Security Update)`	Moderate	Spoofing	Yes
Windows Server 2025	`5099536 (Security Update)`	Moderate	Spoofing	Yes
Windows Server 2025 (Server Core installation)	`5099536 (Security Update)`	Moderate	Spoofing	Yes

Patches

3 patches

Article	Type	Restart
`5101650`	Security Update	Yes
`5101649`	Security Update	Yes
`5099536`	Security Update	Yes

Exploits & PoC

No public exploit or PoC has been linked for this CVE yet. When available, references are sourced from public repositories and may be unverified or non-functional — review carefully before use.

Detection Rules

No public Sigma or Nuclei detection rule has been mapped to this CVE yet. Coverage is concentrated on exploited / high-profile vulnerabilities; check SigmaHQ for updates.

Acknowledgments

Malcolm Stagg with SODIUM-24, LLC

References

MSRC Advisory MITRE NVD