dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-40406

HIGH · 7.5 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 →
84/100
Remediation priority · High
Remotely reachable No privileges 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
Use after free in Windows TCP/IP allows an unauthorized attacker to disclose information over a network.

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 use-after-free vulnerability in the Windows TCP/IP stack allows an unauthenticated remote attacker to trigger the vulnerability by sending specially crafted network packets, leading to disclosure of sensitive memory contents.

MitigationApply the Microsoft security update for CVE-2026-40406 to all affected Windows systems; prioritize internet-facing and high-value assets.

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

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

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. Check installed Windows build number
    Run 'winver' from command prompt or 'systeminfo | findstr /B /C:"OS Name" /C:"Build"' to retrieve the exact build number
    Affected if Build number is below the safe threshold for your Windows version (10.0.14393.9140 for 1607, 10.0.17763.8755 for 1809, 10.0.19044.7291 for 21h2, 10.0.19045.7291 for 22h2, 10.0.22631.7079 for 11 23h2, 10.0.26100.8390 for 11 24h2, 10.0.26200.8390 for 11 25h2, 10.0.28000.2113 for 11 26h1)
  2. Identify Windows version family
    Run 'winver' or check System Properties to determine if you are on Windows 10 1607, 1809, 21h2, 22h2, or Windows 11 23h2/24h2/25h2/26h1
    Affected if The version matches any of the affected products listed in the CVE
  3. Verify TCP/IP stack is enabled
    Check network adapter status via Control Panel > Network and Internet > Network Connections, or run 'netsh interface show interface' to confirm TCP/IP protocol is bound to active network adapters
    Affected if TCP/IP is bound and active on any network adapter (this is the default state for most Windows installations)
  4. Confirm network exposure
    Review which network adapters are active (Ethernet, Wi-Fi, VPN) using 'ipconfig /all' and identify if the system has any internet-facing or routable IP addresses
    Affected if The system has active network connectivity, particularly if it is directly exposed to untrusted networks

You are affected if your Windows build number falls below the safe threshold for your specific Windows version family and the TCP/IP stack is enabled (which is the default configuration).

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 the Microsoft security update for CVE-2026-40406 to all affected Windows systems; prioritize internet-facing and high-value assets.

Recommended fix High confidence

Upgrade to the respective fixed build: Windows 10 1607 to 10.0.14393.9140, Windows 10 1809 to 10.0.17763.8755, Windows 10 21h2 to 10.0.19044.7291, Windows 10 22h2 to 10.0.19045.7291, Windows 11 23h2 to 10.0.22631.7079, Windows 11 24h2 to 10.0.26100.8390, Windows 11 25h2 to 10.0.26200.8390, or Window

  1. Identify the current Windows version and build number by running 'winver' or 'systeminfo' in Command Prompt
  2. Determine which version branch your system is on (e.g., Windows 10 22h2, Windows 11 23h2) from the build number
  3. For Windows 10 systems: Navigate to Settings > Update & Security > Windows Update and check for updates
  4. For Windows 11 systems: Navigate to Settings > Windows Update and check for updates
  5. Alternatively, manually download and install the specific monthly security update from the Microsoft Update Catalog matching your Windows version (e.g., KB506XXXX for the respective month)
  6. After updates are installed, restart the system to apply the TCP/IP stack patches
  7. Verify the installed build number matches or exceeds the fixed version for your branch (e.g., 10.0.19045.7291 for Win10 22h2) using 'winver'
Caveat Standard Windows cumulative updates typically have minimal breaking changes; verify application compatibility after patching

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 / QA1.0 h
10.0 hours of engineering $1,750
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Scan for this in your stack

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dbcve dependency scanner

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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-2026-40406 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