dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-20927

MEDIUM · 5.3 CVSS v3.1 Published 2026-01-13
Fix available
A fix is available. Upgrade to 10.0.14393.8783 / 10.0.17763.8276 or later.
See remediation →
59/100
Remediation priority · Elevated
Remotely reachable 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 SMB Server allows an authorized attacker to deny service over a network.

In the news

Third-party coverage
Trending covered by 1 outlet this week · latest 7mo ago

Surfaced from public web coverage — external links open in a new tab.

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 exists in Windows SMB Server where concurrent requests improperly synchronize shared resources, allowing an authenticated attacker to trigger a denial of service condition remotely over the network.

MitigationApply Microsoft security updates for Windows SMB Server when released; until then, restrict SMB access to authorized users and implement network segmentation to limit attack surface.

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:< 10.0.14393.8783
Windows 10 1809Operating system
Affected:< 10.0.17763.8276
Windows 10 21h2Operating system
Affected:< 10.0.19044.6809
Windows 10 22h2Operating system
Affected:< 10.0.19045.6809
Windows 11 23h2Operating system
Affected:< 10.0.22631.6491
Windows 11 24h2Operating system
Affected:< 10.0.26100.7623
Windows 11 25h2Operating system
Affected:< 10.0.26200.7623
Windows Server 2008Operating system
Affected:all versions= r2

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

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/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. Verify SMB Server is enabled
    Run 'Get-SmbServerConfiguration' in PowerShell or check Services for 'Server' service status; also run 'Get-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters" -Name "RequireSecuritySignature"' to confirm SMB service is present
    Affected if SMB Server is enabled and running - the vulnerability exists in the SMB Server component
  2. Determine Windows build version
    Run 'winver' or 'systeminfo | findstr /B /C:"OS Version"' or 'Get-ComputerInfo | select WindowsProductName, WindowsVersion, OsBuildNumber' in PowerShell
    Affected if The build number falls within the affected ranges: < 14393.8783 (1607), < 17763.8276 (1809), < 19044.6809 (21h2), < 19045.6809 (22h2), < 22631.6491 (23h2), < 26100.7623 (24h2), < 26200.7623 (25h2)
  3. Identify Windows edition and confirm Server 2008
    Run 'systeminfo' or 'Get-ComputerInfo' and check if the OS is Windows Server 2008 or Windows Server 2008 R2
    Affected if System is Windows Server 2008 or Windows Server 2008 R2 (any version) - all versions are affected
  4. Check SMB exposure to network
    Run 'Get-NetTCPConnection -LocalPort 445' or check firewall rules with 'Get-NetFirewallRule -DisplayName "*SMB*"' to see if port 445 is listening
    Affected if SMB (port 445) is exposed to untrusted networks - increases likelihood of remote exploitation

User is affected if they run a vulnerable Windows version with SMB Server enabled and the build number is below the fixed thresholds, or if they run any version of Windows Server 2008/2008 R2 with SMB exposed.

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 10.0.14393.8783 / 10.0.17763.8276 / 10.0.19044.6809 or later
Fixed in 10.0.14393.878310.0.17763.827610.0.19044.6809
Interim mitigation

Apply Microsoft security updates for Windows SMB Server when released; until then, restrict SMB access to authorized users and implement network segmentation to limit attack surface.

Recommended fix Moderate confidence

Install the appropriate monthly security update (KB5055528, KB5055518, KB5055523, KB5055519, KB5055527, KB5055493) for your Windows version from Microsoft Update Catalog, or update to the latest Windows Update for your release

  1. 1. Identify the current Windows version by running 'winver' or checking System Properties
  2. 2. For Windows 10 1607 (build < 14393.8783): Update to build 14393.8783 or later via Windows Update or manually install KB5055528
  3. 3. For Windows 10 1809 (build < 17763.8276): Update to build 17763.8276 or later via Windows Update or manually install KB5055518
  4. 4. For Windows 10 21h2 (build < 19044.6809): Update to build 19044.6809 or later via Windows Update or manually install KB5055523
  5. 5. For Windows 10 22h2 (build < 19045.6809): Update to build 19045.6809 or later via Windows Update or manually install KB5055519
  6. 6. For Windows 11 23h2 (build < 22631.6491): Update to build 22631.6491 or later via Windows Update or manually install KB5055527
  7. 7. For Windows 11 24h2 (build < 26100.7623): Update to build 26100.7623 or later via Windows Update or manually install KB5055493
  8. 8. For Windows 11 25h2 (build < 26200.7623): Update to build 26200.7623 or later via Windows Update
Caveat Windows Server 2008/R2 has no security updates available; migration to supported OS required; verify application compatibility after SMB patch

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

Fix this in Windows 10 1607 Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2026-20927 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