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CVE-2026-56181 is an origin validation error in Windows Network Address Translation (NAT) used by Hyper-V. The flaw affects NAT connection-state handling and allows a host on an adjacent network segment sharing the same NAT infrastructure to manipulate or abuse NAT state in a way that breaks origin validation assumptions. In the broader NatJack attack class, this weakness can be used to interfere with active network sessions by altering how NAT mappings are associated with traffic, enabling spoofed traffic to be accepted as if it originated from a legitimate flow. Reported affected releases include Windows 11 24H2 before 26100.8875, Windows 11 25H2 before 26200.8875, Windows 11 26H1 before 28000.2525, and Windows Server 2025 before 26100.33158.
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No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
5 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A vulnerability in Windows NAT for Hyper-V associated with the NatJack attack class, enabling manipulation of NAT connection states that can contribute to TCP session hijacking, DNS spoofing, port disclosure, or NAT table exhaustion.
An origin-validation error in Windows NAT used by Hyper-V that enables spoofing from an adjacent network as part of the broader NatJack attack class.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.