CVE-2026-56181: Origin validation error in Windows Network Address Translation (NAT) allows an unauthorized attacker to perfor

Q: How do I fix CVE-2026-56181?

windows 11 24h2: upgrade to 10.0.26100.8875; windows 11 25h2: upgrade to 10.0.26200.8875; windows 11 26h1: upgrade to 10.0.28000.2525. Exact commands for each OS are on this page.

Q: Is CVE-2026-56181 being exploited?

CVE-2026-56181 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-56181 affect?

CVE-2026-56181 affects windows 11 24h2, windows 11 25h2, windows 11 26h1. Severity is high (CVSS 8.3). Origin validation error in Windows Network Address Translation (NAT) allows an unauthorized attacker to perform spoofing over an adjacent network.

Q: How urgent is CVE-2026-56181?

Priority 39/100. High severity; On your watchlist

Routine

HIGH 8.3WATCHLISTUPGRADEUPGRADEUPGRADE

CVE-2026-56181 is a high-severity flaw (CVSS 8.3) affecting windows 11 24h2, windows 11 25h2, windows 11 26h1. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

High severity
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.3 (High)
Attack vector	Adjacent network
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 80%)
CISA exploited list	No
Weakness	CWE-346
Published	2026-07-14
Last modified	2026-07-22

Publisher (CNA): Microsoft Corporation · Vendor: microsoft

Last updated 2026-07-22 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-14 18:18 UTCPublished CVE record published
2026-07-22 16:18 UTCUpdated Record last modified

microsoft windows 11 24h2 UPGRADE

Affected: < 10.0.26100.8875

Fixed in: 10.0.26100.8875

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

microsoft windows 11 25h2 UPGRADE

Affected: < 10.0.26200.8875

Fixed in: 10.0.26200.8875

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

microsoft windows 11 26h1 UPGRADE

Affected: < 10.0.28000.2525

Fixed in: 10.0.28000.2525

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

microsoft windows server 2025 UPGRADE

Affected: < 10.0.26100.33158

Fixed in: 10.0.26100.33158

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-56181?

windows 11 24h2: upgrade to 10.0.26100.8875; windows 11 25h2: upgrade to 10.0.26200.8875; windows 11 26h1: upgrade to 10.0.28000.2525. Exact commands for each OS are on this page.

Is CVE-2026-56181 being exploited?

CVE-2026-56181 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-56181 affect?

CVE-2026-56181 affects windows 11 24h2, windows 11 25h2, windows 11 26h1. Severity is high (CVSS 8.3). Origin validation error in Windows Network Address Translation (NAT) allows an unauthorized attacker to perform spoofing over an adjacent network.

How urgent is CVE-2026-56181?

Priority 39/100. High severity; On your watchlist

Software pages

Windows vulnerabilities · Windows Server vulnerabilities

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References

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