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

Severity: high (CVSS 8.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-11 · updated 2026-10-30
Weakness: CWE-346

Description

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

Affected products

Microsoft Windows 11: before 10.0.26100.9106 — fixed in 10.0.26100.9106
Microsoft Windows 11 25H2: before 10.0.26200.9106 — fixed in 10.0.26200.9106
Microsoft Windows 11 version 26H1: before 10.0.28000.2704 — fixed in 10.0.28000.2704
Microsoft Windows Server 2025: before 10.0.26100.33222 — fixed in 10.0.26100.33222
Microsoft Windows 11: from 10.0.26100.0 before 10.0.26100.9168 — fixed in 10.0.26100.9168
Microsoft Windows 11 25H2: from 10.0.26200.0 before 10.0.26200.9168 — fixed in 10.0.26200.9168
Microsoft Windows 11 version 26H1: from 10.0.28000.0 before 10.0.28000.2704 — fixed in 10.0.28000.2704
Microsoft Windows Server 2025: from 10.0.26100.0 before 10.0.26100.33296 — fixed in 10.0.26100.33296

How to fix

Upgrade to a fixed version: Microsoft Windows 11 10.0.26100.9106; Microsoft Windows 11 25H2 10.0.26200.9106; Microsoft Windows 11 version 26H1 10.0.28000.2704; Microsoft Windows Server 2025 10.0.26100.33222; Microsoft Windows 11 10.0.26100.9168; Microsoft Windows 11 25H2 10.0.26200.9168; Microsoft Windows 11 version 26H1 10.0.28000.2704; Microsoft Windows Server 2025 10.0.26100.33296. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56179

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