dbcve.org
Windows 10 1607Operating system · Microsoft

CVE-2026-40403

HIGH · 8.8 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 →
90/100
Remediation priority · Urgent
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 Win32K - GRFX allows an authorized attacker to execute code 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 Win32K graphics subsystem (GRFX) allows an authorized local attacker to execute arbitrary code via specially crafted graphical operations.

MitigationApply Microsoft security updates for Windows when available; prioritize patching endpoint systems given the local code execution risk.

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
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/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 version and build number
    Open Command Prompt or PowerShell and run: winver or systeminfo | findstr /B /C:"OS Name" /C:"OS Version" or [System.Environment]::OSVersion.Version in PowerShell
    Affected if The installed version is lower than any of the following: 10.0.14393.9140 (Win10 1607), 10.0.17763.8755 (Win10 1809), 10.0.19044.7291 (Win10 21h2), 10.0.19045.7291 (Win10 22h2), 10.0.22631.7079 (Win11 23h2), 10.0.26100.8390 (Win11 24h2), 10.0.26200.8390 (Win11 25h2), 10.0.28000.2113 (Win11 26h1)
  2. Verify Win32K.sys driver presence
    Check that the Win32K graphics subsystem driver exists at System32\drivers\win32k.sys or via PowerShell: Get-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Services\Win32k' -ErrorAction SilentlyContinue
    Affected if The Win32k driver is present and loaded (standard on all affected Windows versions)
  3. Confirm system is not a server edition
    Run: systeminfo | findstr /C:"OS Name" or check System Information in Control Panel - look for Server editions (Windows Server)
    Affected if The installed OS is a client Windows edition (Windows 10 or 11) matching the affected version ranges above

Your environment is affected if you are running any of the listed Windows 10 or Windows 11 versions below the specified build numbers, and the Win32K.sys graphics driver is present (which is the default configuration for these Windows editions).

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 when available; prioritize patching endpoint systems given the local code execution risk.

Recommended fix High confidence

Upgrade to the specific Windows build number for your release channel (e.g., Windows 10 22h2 -> 10.0.19045.7291 or later; Windows 11 24h2 -> 10.0.26100.8390 or later)

  1. 1. Identify the current Windows version by running `winver` or `systeminfo` in Command Prompt
  2. 2. Determine which Windows 10 or 11 release channel your system is on (e.g., 21h2, 22h2, 23h2, 24h2, 25h2, or 26h1)
  3. 3. For Windows 10 1607 systems: upgrade to Windows 10 build 10.0.14393.9140 or later via Windows Update or your organization's update management solution
  4. 4. For Windows 10 1809 systems: upgrade to Windows 10 build 10.0.17763.8755 or later
  5. 5. For Windows 10 21h2 systems: upgrade to Windows 10 build 10.0.19044.7291 or later
  6. 6. For Windows 10 22h2 systems: upgrade to Windows 10 build 10.0.19045.7291 or later
  7. 7. For Windows 11 23h2 systems: upgrade to Windows 11 build 10.0.22631.7079 or later
  8. 8. For Windows 11 24h2 systems: upgrade to Windows 11 build 10.0.26100.8390 or later
Caveat Standard Windows update risks apply: ensure critical data is backed up before applying updates; some legacy applications may require compatibility testing after major version updates

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
  • Testing4.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,120
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,392.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2026-40403 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

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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-2026-40403 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