dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-40399

HIGH · 7.8 CVSS v3.1 Published 2026-05-12
Fix available
A fix is available. Upgrade to 10.0.14393.9140 / 10.0.17763.8755 or later.
See remediation →
80/100
Remediation priority · High
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Concurrent execution using shared resource with improper synchronization ('race condition') in Windows TCP/IP allows an authorized attacker to elevate privileges locally.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

A race condition vulnerability exists in the Windows TCP/IP stack where improper synchronization of shared resources allows a locally authenticated attacker to elevate privileges to SYSTEM level by winning a race condition.

MitigationApply Microsoft security updates for Windows TCP/IP when released; given the high CVSS and local privilege escalation vector, prioritize patching on all affected Windows systems.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Windows 10 1607Operating system
Affected:< 10.0.14393.9140
Windows 10 1809Operating system
Affected:< 10.0.17763.8755
Windows 10 21h2Operating system
Affected:< 10.0.19044.7291
Windows 10 22h2Operating system
Affected:< 10.0.19045.7291
Windows 11 23h2Operating system
Affected:< 10.0.22631.7079
Windows 11 24h2Operating system
Affected:< 10.0.26100.8390
Windows 11 25h2Operating system
Affected:< 10.0.26200.8390
Windows 11 26h1Operating system
Affected:< 10.0.28000.2113

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Windows build version
    Run 'winver' from the Run dialog or execute 'systeminfo | findstr /B /C:"OS Name" /C:"OS Version"' in Command Prompt to obtain the exact build number
    Affected if The displayed build number falls below any of these thresholds: 14393.9140 (Win10 1607), 17763.8755 (Win10 1809), 19044.7291 (Win10 21h2/22h2), 22631.7079 (Win11 23h2), 26100.8390 (Win11 24h2), 26200.8390 (Win11 25h2), or 28000.2113 (Win11 26h1)
  2. Confirm TCP/IP stack is in use
    Verify network connectivity is enabled; open Network Connections (ncpa.cpl), right-click your active network adapter, and select Status. Alternatively, run 'netsh interface ipv4 show interfaces' to confirm TCP/IPv4 is bound
    Affected if TCP/IP is a default component in Windows and is typically enabled on any system with network access; most standard installations are affected if the build version is vulnerable
  3. Verify local user authentication context
    Check for existing local user accounts by running 'net user' in Command Prompt. The vulnerability requires an attacker to have authenticated local access to win the race condition
    Affected if The presence of any local user account (beyond the built-in Administrator) indicates a potential attack vector, though this vulnerability can affect any authenticated local user

A system is affected if it runs any Windows version with a build number lower than the thresholds listed for its specific Windows release (10 or 11, version/feature update).

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 10.0.14393.9140 / 10.0.17763.8755 / 10.0.19044.7291 or later
Fixed in 10.0.14393.914010.0.17763.875510.0.19044.7291
Interim mitigation

Apply Microsoft security updates for Windows TCP/IP when released; given the high CVSS and local privilege escalation vector, prioritize patching on all affected Windows systems.

Recommended fix High confidence

Install the appropriate Windows security update containing the fix for CVE-2026-40399 (TCP/IP privilege elevation) matching your Windows version - builds range from 10.0.14393.9140 to 10.0.28000.2113 depending on Windows release

  1. 1. Identify the current Windows version and build number by running 'winver' or 'systeminfo' in Command Prompt
  2. 2. Determine which Windows 10 or 11 version and build is currently installed
  3. 3. For Windows 10 1607: Upgrade to build 10.0.14393.9140 or later
  4. 4. For Windows 10 1809: Upgrade to build 10.0.17763.8755 or later
  5. 5. For Windows 10 21h2: Upgrade to build 10.0.19044.7291 or later
  6. 6. For Windows 10 22h2: Upgrade to build 10.0.19045.7291 or later
  7. 7. For Windows 11 23h2: Upgrade to build 10.0.22631.7079 or later
  8. 8. For Windows 11 24h2: Upgrade to build 10.0.26100.8390 or later
Caveat Standard Windows cumulative update apply; minor restart required - no known breaking changes for this privilege escalation patch

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Windows 10 1607 Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing4.0 h
  • Review / QA2.0 h
15.0 hours of engineering $2,640
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-40399 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data