dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-40407

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
Heap-based buffer overflow in Windows Common Log File System Driver 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

Heap-based buffer overflow in Windows Common Log File System Driver (CLFS), a kernel-mode logging subsystem. The vulnerability allows a locally authenticated attacker to overflow heap memory allocations in kernel context, potentially achieving arbitrary code execution and local privilege elevation from medium integrity to SYSTEM.

MitigationApply Microsoft security updates for Windows addressing this CLFS vulnerability when released; until then, limit local system access to trusted administrators only and monitor for suspicious process activity.

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. Check Windows build number
    Run 'winver' or 'systeminfo | findstr /B /C:"OS Version"' or 'ver' command to obtain the full Windows version and build number
    Affected if The build number is lower than any of these thresholds: 14393.9140 (Windows 10 1607), 17763.8755 (Windows 10 1809), 19044.7291 (Windows 10 21h2), 19045.7291 (Windows 10 22h2), 22631.7079 (Windows 11 23h2), 26100.8390 (Windows 11 24h2), 26200.8390 (Windows 11 25h2), or 28000.2113 (Windows 11 26h1)
  2. Identify Windows edition family
    Check if the system is Windows 10 1607, 1809, 21h2, 22h2, or Windows 11 23h2, 24h2, 25h2, 26h1 using 'systeminfo' or 'winver' output
    Affected if The system runs any of the listed Windows 10 or Windows 11 versions AND the build number is below the corresponding threshold from step 1
  3. Verify CLFS driver presence
    Confirm the clfs.sys driver exists in the system: check 'C:\Windows\System32\drivers\clfs.sys' or run 'driverquery /v | findstr clfs'
    Affected if The CLFS driver (clfs.sys) is present on the system, which is true for all standard Windows installations since CLFS is a built-in kernel logging subsystem

You are affected if your Windows build number is lower than the version-specific threshold listed for your Windows edition, and the clfs.sys driver is present on the system.

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 addressing this CLFS vulnerability when released; until then, limit local system access to trusted administrators only and monitor for suspicious process activity.

Recommended fix High confidence

Windows 10 1607 (10.0.14393.9140+), Windows 10 1809 (10.0.17763.8755+), Windows 10 21h2 (10.0.19044.7291+), Windows 10 22h2 (10.0.19045.7291+), Windows 11 23h2 (10.0.22631.7079+), Windows 11 24h2 (10.0.26100.8390+), Windows 11 25h2 (10.0.26200.8390+), Windows 11 26h1 (10.0.28000.2113+)

  1. Check current Windows version by running 'winver' or 'systeminfo' in Command Prompt
  2. Identify which Windows 10 or 11 version range your current installation falls into from the affected versions list
  3. Apply Windows Updates: Open Settings > Windows Update > Check for Updates
  4. Install all available cumulative updates until the build number reaches or exceeds the fixed version for your Windows release
  5. For Windows 10 1607, upgrade to build 10.0.14393.9140 or later
  6. For Windows 10 1809, upgrade to build 10.0.17763.8755 or later
  7. For Windows 10 21h2, upgrade to build 10.0.19044.7291 or later
  8. For Windows 10 22h2, upgrade to build 10.0.19045.7291 or later
Caveat Standard Windows update risks apply - ensure backups of critical data exist before applying updates

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
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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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-2026-40407 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