CVE-2026-56181

Adjacent-network spoofing via unvalidated packet origin

Published Jul 14, 2026 · Updated Jul 14, 2026

Origin validation error in Windows NAT allows remote attackers to spoof network traffic over an adjacent network without authentication. Microsoft has not disclosed which NAT code path fails to validate packet origin or the precise crafted traffic it accepts. Exploitation requires adjacent-network access and high complexity; successful spoofing can compromise data and service availability across a security boundary.

CVSS severity8.3
High
EPSS probability0.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Origin validation error in Windows NAT allows remote attackers to spoof network traffic over an adjacent network without authentication. Microsoft has not disclosed which NAT code path fails to validate packet origin or the precise crafted traffic it accepts. Exploitation requires adjacent-network access and high complexity; successful spoofing can compromise data and service availability across a security boundary.

The record

CVE
CVE-2026-56181
Published
Jul 14, 2026
Updated
Jul 14, 2026
Vendor
Microsoft
Product
Windows Server 2025 (Server Core installation)
Classifications
CWE-346
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 14, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.0.26100.0 <10.0.26100.33158

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Microsoft · Windows Server 2025 (Server Core installation)version=10.0.26100.0 <10.0.26100.33158
Microsoft · Windows 11, version 25H2version=10.0.26200.0 <10.0.26100.8875
Microsoft · Windows 11, version 24H2version=10.0.26100.0 <10.0.26100.8875
Microsoft · Windows 11, version 26H1version=10.0.28000.0 <10.0.28000.2525
Microsoft · Windows Server 2025version=10.0.26100.0 <10.0.26100.33158

Published CVSS scores

8.3Microsoft CorporationCVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-346Origin Validation Error

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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