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CVE-2026-56179

HIGH 8.3

Published 2026-08-11 · Last modified 2026-08-21

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

ELEVATED IMPACT

Severe if exploited (CVSS 8.3), but no known exploitation and low modeled probability. Patch on a normal cadence.

Exploitation likelihood

0.2%chance of exploitation in 30 days · 15th percentile

○ In CISA KEV ○ Public exploit / PoC

Impact if exploited

8.3CVSS 3.1 · HIGH

  • ConfidentialityHigh
  • IntegrityHigh
  • AvailabilityHigh

What an attacker needs

  • ⚠Access: Must sit on the same / adjacent network
  • ✓Privileges: No account or privileges required
  • ✓User interaction: No user interaction needed
  • ⚠Complexity: Needs a race window or specific setup

✓ lowers the bar for an attacker · ⚠ raises it

Proof of concept & exploit code

Test against your own equipment

curl -s https://vulnpedia.com/cve/CVE-2026-56179/poc.jsonMachine-readable PoC index for this CVE (for automation).

Listed for defensive triage, patch verification, and authorized testing on systems you own. Machine-readable: /cve/CVE-2026-56179/poc.json

Affected

Vendors Microsoft

Products Windows 11 Version 24h2 Windows 11 Version 25h2 Windows 11 Version 26h1 Windows Server 2025 Windows Server 2025 (Server Core Installation) Windows 11 24h2 Windows 11 25h2 Windows 11 26h1

Weakness (CWE)

  • CWE-346: : Origin Validation Error

CVSS vector

CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C

Known Affected Software Configurations

VendorProductVersion range
MicrosoftWindows 11 24h2< 10.0.26100.9106
MicrosoftWindows 11 24h2< 10.0.26100.9106
MicrosoftWindows 11 25h2< 10.0.26200.9106
MicrosoftWindows 11 25h2< 10.0.26200.9106
MicrosoftWindows 11 26h1< 10.0.28000.2704
MicrosoftWindows 11 26h1< 10.0.28000.2704
MicrosoftWindows Server 2025< 10.0.26100.33222

All CVSS metrics

  • HIGH 8.3 v3.1 · CNA Primary
    CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C
  • HIGH 8.3 v3.1 · NVD Secondary
    CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

References

Patches & mitigations

Sources: NVD · CVE.org · EPSS