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365 AppsApplication · Microsoft

CVE-2026-40359

HIGH · 7.8 CVSS v3.1 Published 2026-05-12
Fix available
A fix is available. Upgrade to 16.0.10417.20128 or later.
See remediation →
81/100
Remediation priority · High
No privileges

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 Microsoft Office Excel allows an unauthorized 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

A use-after-free vulnerability exists in Microsoft Office Excel where memory is accessed after being freed, allowing an attacker to manipulate heap memory and achieve arbitrary code execution locally on the target system.

MitigationApply Microsoft security updates for Excel immediately, ensure Microsoft Office is kept current via automatic updates, and enable Exploit Protection in Microsoft Defender where available.

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
365 AppsApplication
Affected:all versions
ExcelApplication
Affected:= 2016
OfficeApplication
Affected:= 2019
Office Long Term Servicing ChannelApplication
Affected:= 2021= 2024
Office Online ServerApplication
Affected:< 16.0.10417.20128

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
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/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. Verify Excel is installed
    Check for the presence of EXCEL.EXE in typical installation paths: %ProgramFiles%\Microsoft Office\root\Office16 (or Office15/Office14 depending on version), %ProgramFiles%\Microsoft Office\Office16, or %ProgramFiles% (x86)\Microsoft Office\Office16. Alternatively, check the Windows Registry under HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\EXCEL.EXE
    Affected if Excel is installed and the CVE applies to the installed Excel version per the affected version ranges provided.
  2. Determine installed Excel version via file properties
    Right-click EXCEL.EXE in the installation directory, select Properties, then go to the Details tab to view the File Version. Alternatively, open Excel, go to File > Account > About Excel, or run 'winver' command for Office version when Excel is the primary Office app.
    Affected if The displayed version matches or falls within the affected ranges: Excel 2016 (= 2016), Office 2019 (= 2019), LTSC 2021 (= 2021), LTSC 2024 (= 2024), or Microsoft 365 Apps (all versions).
  3. Check Office version via registry for Office Click-to-Run
    For Microsoft 365 Apps or subscription Office, check the registry key: HKLM\SOFTWARE\Microsoft\Office\ClickToRun\Configuration or HKLM\SOFTWARE\Microsoft\Office\16.0\Common\InstallRoot, looking for the Version key value.
    Affected if The registry shows a Microsoft 365 Apps installation (all versions affected) or matches the specific version numbers listed.
  4. Determine Microsoft Office Long Term Servicing Channel version
    For LTSC 2021 or LTSC 2024 installations, check the installed version through Excel's About dialog (File > Account > About Excel) or via the Office Setup program in Programs and Features. LTSC versions are identified by perpetual license, not subscription.
    Affected if The installation is Office LTSC 2021 (= 2021) or LTSC 2024 (= 2024), as both are listed as affected.
  5. Check Microsoft Office Online Server version
    On the server hosting Office Online Server, open the Office Online Server Management Shell and run Get-OfficeOnlineServerVersion, or navigate to the installation directory (typically C:\Program Files\Microsoft Office Web Server\15\ or 16\) and check the version of WacServer.exe or WacBootstrapper.exe via Properties > Details.
    Affected if The installed build number is less than 16.0.10417.20128.

A system is affected if it runs any version of Microsoft 365 Apps, Excel 2016, Office 2019, Office LTSC 2021, Office LTSC 2024, or Office Online Server with a build below 16.0.10417.20128.

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 16.0.10417.20128 or later
Fixed in 16.0.10417.20128
Interim mitigation

Apply Microsoft security updates for Excel immediately, ensure Microsoft Office is kept current via automatic updates, and enable Exploit Protection in Microsoft Defender where available.

Recommended fix Moderate confidence

Apply Microsoft Office security updates released after the CVE publication date (latest monthly security update for Office)

  1. Open Microsoft Excel or any Office application
  2. Go to File > Account > Update Options
  3. Click 'Update Now' to check for and install the latest security updates
  4. Alternatively, visit aka.ms/officeupdates to download the latest patches
  5. Restart Excel after the update is applied
  6. Verify the update was installed by checking the Office version in File > Account
Caveat Standard Office security updates typically have no breaking changes and are drop-in replacements

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

Fix this in 365 Apps Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
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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-2026-40359 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