dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-27921

HIGH · 7.0 CVSS v3.1 Published 2026-04-14
Fix available
A fix is available. Upgrade to 10.0.14393.9060 / 10.0.17763.8644 or later.
See remediation →
72/100
Remediation priority · Elevated
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 concurrent execution shares a resource without proper synchronization. An authorized local attacker can exploit this timing vulnerability to manipulate the shared resource state and elevate privileges to a higher level.

MitigationApply the relevant Microsoft security patch for Windows TCP/IP when available. Until then, minimize local attack surface by restricting physical access and ensuring users run with least privilege. Monitor for unusual process behavior or privilege escalation attempts.

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:< 10.0.14393.9060
Windows 10 1809Operating system
Affected:< 10.0.17763.8644
Windows 10 21h2Operating system
Affected:< 10.0.19044.7184
Windows 10 22h2Operating system
Affected:< 10.0.19045.7184
Windows 11 23h2Operating system
Affected:< 10.0.22631.6936
Windows 11 24h2Operating system
Affected:< 10.0.26100.8246
Windows 11 25h2Operating system
Affected:< 10.0.26200.8246
Windows 11 26h1Operating system
Affected:< 10.0.28000.1836

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
High
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:H/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 version and build number
    Run 'winver' from command prompt or 'systeminfo' from command line. Note the OS Version and Build Number displayed.
    Affected if The build number is below any of these thresholds: 14393.9060 (Windows 10 1607), 17763.8644 (Windows 10 1809), 19044.7184 (Windows 10 21h2/22h2), 22631.6936 (Windows 11 23h2), 26100.8246 (Windows 11 24h2/25h2), or 28000.1836 (Windows 11 26h1)
  2. Confirm TCP/IP stack is in use
    Verify network adapters are configured. Open Control Panel > Network and Internet > Network Connections, or run 'ipconfig /all' from command prompt. Confirm at least one active network adapter has an IP address assigned.
    Affected if TCP/IP is enabled on any network adapter - this is the default state on Windows systems with network connectivity
  3. Check installed security updates
    Open Settings > Windows Update > View update history, or run 'wmic qfe list' from command prompt. Look for Microsoft security updates related to TCP/IP or networking stack.
    Affected if No recent TCP/IP or networking-related security patches are installed, and the Windows build number falls within the affected version ranges listed above

A system is affected if it runs a Windows version with a build number lower than the patched thresholds AND has TCP/IP networking enabled, which is the default configuration on most Windows systems.

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 10.0.14393.9060 / 10.0.17763.8644 / 10.0.19044.7184 or later
Fixed in 10.0.14393.906010.0.17763.864410.0.19044.7184
Interim mitigation

Apply the relevant Microsoft security patch for Windows TCP/IP when available. Until then, minimize local attack surface by restricting physical access and ensuring users run with least privilege. Monitor for unusual process behavior or privilege escalation attempts.

Recommended fix High confidence

Upgrade to the specified build version for your Windows release: 10.0.14393.9060 (Win10 1607), 10.0.17763.8644 (Win10 1809), 10.0.19044.7184 (Win10 21h2), 10.0.19045.7184 (Win10 22h2), 10.0.22631.6936 (Win11 23h2), 10.0.26100.8246 (Win11 24h2), 10.0.26200.8246 (Win11 25h2), or 10.0.28000.1836 (Win11

  1. Identify the current Windows version and build number by running 'winver' or 'systeminfo' in Command Prompt
  2. Determine which Windows 10 or 11 version is running from the list of affected versions
  3. Apply the appropriate Windows Update or manually download and install the cumulative update that includes the fix for this vulnerability
  4. For Windows 10 1607: Upgrade to build 10.0.14393.9060 or later
  5. For Windows 10 1809: Upgrade to build 10.0.17763.8644 or later
  6. For Windows 10 21h2: Upgrade to build 10.0.19044.7184 or later
  7. For Windows 10 22h2: Upgrade to build 10.0.19045.7184 or later
  8. For Windows 11 23h2: Upgrade to build 10.0.22631.6936 or later
Caveat Standard Windows update risks apply - ensure backups and test in staging if possible; some enterprise policies may require coordinated rollout

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

Fix this in Windows 10 1607 Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,600
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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-2026-27921 in production — separate from our analysis above.

No notes yet

Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.

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