dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-40409

HIGH · 7.8 CVSS v3.1 Published 2026-06-09
Fix available
A fix is available. Upgrade to 10.0.14393.9234 / 10.0.17763.8880 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
Windows Universal Disk Format File System Driver (UDFS) Elevation of Privilege Vulnerability

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

This is an Elevation of Privilege vulnerability in the Windows Universal Disk Format (UDFS) file system driver. The vulnerability exists in kernel-mode code and allows a local attacker to escalate privileges from a standard user account to SYSTEM-level access. Exploitation would involve triggering a flaw in the UDFS driver's handling of disk operations.

MitigationApply the Microsoft security update addressing CVE-2026-40409 once available through Windows Update or manual patch deployment. For defense-in-depth, restrict user access to mounting UDFS-formatted media and monitor for unauthorized kernel-level module loading.

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:< 10.0.14393.9234
Windows 10 1809Operating system
Affected:< 10.0.17763.8880
Windows 10 21h2Operating system
Affected:< 10.0.19044.7417
Windows 10 22h2Operating system
Affected:< 10.0.19045.7417
Windows 11 23h2Operating system
Affected:< 10.0.22631.7219
Windows 11 24h2Operating system
Affected:< 10.0.26100.8655
Windows 11 25h2Operating system
Affected:< 10.0.26200.8655
Windows 11 26h1Operating system
Affected:< 10.0.28000.2269

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
    Open Command Prompt or PowerShell and run `winver` or `systeminfo | findstr /B /C:"OS Version"` to obtain the full Windows build number
    Affected if The build number is lower than 14393.9234 for Windows 10 1607, 17763.8880 for Windows 10 1809, 19044.7417 for Windows 10 21h2, 19045.7417 for Windows 10 22h2, 22631.7219 for Windows 11 23h2, 26100.8655 for Windows 11 24h2, 26200.8655 for Windows 11 25h2, or 28000.2269 for Windows 11 26h1
  2. Confirm Windows edition matches affected range
    Run `winver` to verify if your Windows edition (Windows 10 or Windows 11) and version (such as 21h2, 22h2, 23h2, 24h2, 25h2, 26h1) corresponds to the build number you retrieved
    Affected if Your Windows edition and version correspond to a build number that falls below the threshold listed for that specific version in the affected products list
  3. Check if UDF filesystem driver is present
    Open Command Prompt as Administrator and run `sc query udfs` or check driver presence via `driverquery /v | findstr -i udfs`
    Affected if The UDFS driver (udfs.sys) is installed on the system, making the vulnerability potentially exploitable if the version is also vulnerable
  4. Check for mounted UDF volumes
    Run `mountvol` or check Disk Management (diskmgmt.msc) for any removable media or ISO files mounted using the UDF filesystem
    Affected if Any UDF-formatted volumes are currently mounted or accessible on the system

You are affected if your Windows build number falls below the threshold for your specific Windows version and the UDF filesystem 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 10.0.14393.9234 / 10.0.17763.8880 / 10.0.19044.7417 or later
Fixed in 10.0.14393.923410.0.17763.888010.0.19044.7417
Interim mitigation

Apply the Microsoft security update addressing CVE-2026-40409 once available through Windows Update or manual patch deployment. For defense-in-depth, restrict user access to mounting UDFS-formatted media and monitor for unauthorized kernel-level module loading.

Recommended fix High confidence

Windows 10 1607: 10.0.14393.9234 | Windows 10 1809: 10.0.17763.8880 | Windows 10 21h2: 10.0.19044.7417 | Windows 10 22h2: 10.0.19045.7417 | Windows 11 23h2: 10.0.22631.7219 | Windows 11 24h2: 10.0.26100.8655 | Windows 11 25h2: 10.0.26200.8655 | Windows 11 26h1: 10.0.28000.2269

  1. Open Windows Settings and navigate to Windows Update
  2. Click 'Check for updates' to download and install the latest cumulative security update
  3. Alternatively, manually install the appropriate KB patch for your Windows version from the Microsoft Update Catalog
  4. Restart the system after installing the update
  5. Verify the installed build version matches or exceeds the fixed version for your Windows release
Caveat Standard Windows update; no breaking changes expected for this security 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
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
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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-2026-40409 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