EUVD-2026-44316
GHSA-q8r6-qhxq-g78g
Severity by source
AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Adjacent unauthenticated access with a timing-dependent race (AV:A/AC:H/PR:N); an origin-spoofing flaw primarily breaks integrity (I:H) with lesser confidentiality/availability effect, and scope changes across the NAT boundary (S:C).
Primary rating from Vendor (microsoft).
CVSS VectorNVD
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
Lifecycle Timeline
2DescriptionNVD
Origin validation error in Windows Network Address Translation (NAT) allows an unauthorized attacker to perform spoofing over an adjacent network.
AnalysisAI
Spoofing via origin validation error in the Windows Network Address Translation (NAT) component affects Windows 11 (24H2, 25H2, 26H1) and Windows Server 2025, including Server Core installations. An unauthenticated attacker positioned on an adjacent network segment can bypass origin/authentication checks (CWE-346) to impersonate a trusted source, with Microsoft rating scope-changed high impact to confidentiality, integrity, and availability (CVSS 8.3). …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the Windows NAT feature to be active on the target (e.g., Hyper-V virtual switch/default switch, Internet Connection Sharing, Windows container NAT networking, or WSL2 NAT mode) on Windows 11 24H2/25H2/26H1 or Windows Server 2025, and the attacker must be on an adjacent network (AV:A) - the same L2 segment/broadcast domain or a directly linked network, not the routed internet. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H yields 8.3 (High): no privileges or user interaction are required and a scope change (S:C) reflects that compromising the NAT boundary can affect systems beyond the vulnerable component, which drives the score up. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker who has gained a foothold on a device within the same adjacent network as a Windows Server 2025 virtualization host running Windows NAT crafts spoofed packets that impersonate a trusted internal or external endpoint. By repeatedly timing the injection to win the required race condition (AC:H), the attacker defeats the NAT origin check and gets malicious traffic mapped as if it came from a legitimate host, enabling session hijacking or interposition across the NAT boundary. … |
| Remediation | Apply the Microsoft security update for CVE-2026-56181 from the MSRC advisory (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56181); patch is available per vendor, and the exact fixed build/KB numbers for each affected release should be taken directly from that advisory (specific build versions were not enumerated in the provided data, so do not assume a version number). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, identify and inventory all Windows 11 (versions 24H2, 25H2, 26H1) and Windows Server 2025 systems in your environment and assess network segmentation to isolate untrusted adjacent network segments. …
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Same weakness CWE-346 – Origin Validation Error
View allSame technique Authentication Bypass
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External POC / Exploit Code
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