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HIGH severity

CVE-2026-56181 — Windows 11 24h2

HIGH

CVE-2026-56181 is a high-severity (CVSS 8.3) CWE-346 vulnerability in microsoft windows 11 24h2. A fix is available — see the affected versions and patch details below.

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

Published
Updated
Affected
4 products
Patched
See advisory
Exploits
None indexed
Exploitation data as of Oct 11, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • A successful exploit gives an attacker total control of the affected component, not partial access.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-56181.

EPSS Exploitation Probability

via FIRST.org ↗
0.3%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs18th percentile — riskier than 18% of all scored CVEsHighest risk
0.00%0.26%0.52%0.78%0.2%0.3%0.3%0.3%Aug 26Oct 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-56181 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 386,684 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Description

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

Affected Products

4 products · 4 configurations
OS
windows 11 24h2microsoft
< 10.0.26100.8875
range
OS
windows 11 25h2microsoft
< 10.0.26200.8875
range
OS
windows 11 26h1microsoft
< 10.0.28000.2525
range
OS
windows server 2025microsoft
< 10.0.26100.33158
range

Detection & mitigation playbook

Vendor / appliance

  1. Detect

    Inventory every microsoft windows 11 24h2 deployment and check each version against the affected-products list above.

  2. Fix

    Apply the microsoft windows 11 24h2 security patch or hotfix for CVE-2026-56181 on the affected version, following the vendor advisory for your exact build.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

Frequently Asked Questions

Origin validation error in Windows Network Address Translation (NAT) allows an unauthorized attacker to perform spoofing over an adjacent network.
O3 Security · Runtime Protection

Is CVE-2026-56181 being exploited in your environment?

Detect and block the exploit chain at execution, on systems you cannot patch yet.

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CVE-2026-56181: Windows 11 24h2 (High 8.3)