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365 AppsApplication · Microsoft

CVE-2026-40363

HIGH · 8.4 CVSS v3.1 Published 2026-05-12
Fix available
A fix is available. Upgrade to 16.0.19822.20190 or later.
See remediation →
89/100
Remediation priority · High
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
Heap-based buffer overflow in Microsoft Office 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 heap-based buffer overflow vulnerability in Microsoft Office enables an authenticated local attacker to execute arbitrary code. The vulnerability stems from improper memory handling when processing specially crafted Office documents, allowing the attacker to overwrite heap metadata and redirect execution flow.

MitigationApply Microsoft security updates for Office as they become available through Windows Update or the Microsoft Update Catalog. Prioritize patching endpoint systems and verify remediation through vulnerability scanning.

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
365 CopilotApplication
Affected:< 16.0.19822.20190
OfficeApplication
Affected:= 2016= 2019
Office Long Term Servicing ChannelApplication
Affected:= 2021= 2024

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
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:N/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. Identify installed Microsoft Office version
    Open Word or Excel, go to File > Account > About [App] to see the version number, or run 'winword.exe /?' from Command Prompt to display version info
    Affected if Version matches 2016, 2019, LTSC 2021, or LTSC 2024 exactly, OR the version is Microsoft 365 Apps (any version), OR for Microsoft 365 Copilot the version is below 16.0.19822.20190
  2. Check Office update channel configuration
    In Office, go to File > Account > Update Options to see if updates are set to automatically install; for Microsoft 365 Apps, check via File > Account > View Account > About to confirm subscription status
    Affected if Updates are disabled or manual, leaving the installed version unpatched
  3. Verify whether targeted Office applications are in use
    Review which Office applications (Word, Excel, PowerPoint, Outlook) are installed and actively used on the system via Programs and Features or 'Get-AppxPackage' PowerShell command
    Affected if Any of the affected Office applications are installed without the latest security patches applied
  4. Confirm user interaction vector
    The vulnerability is triggered when users open specially crafted Office documents; review email filtering and document handling practices in the environment
    Affected if Users routinely open Office documents from untrusted or external sources without additional scrutiny

A system is affected if it runs Microsoft Office 2016, 2019, LTSC 2021, LTSC 2024, any version of Microsoft 365 Apps, or Microsoft 365 Copilot versions below 16.0.19822.20190 without the corresponding security update applied.

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 16.0.19822.20190 or later
Fixed in 16.0.19822.20190
Interim mitigation

Apply Microsoft security updates for Office as they become available through Windows Update or the Microsoft Update Catalog. Prioritize patching endpoint systems and verify remediation through vulnerability scanning.

Recommended fix Moderate confidence

Latest Microsoft 365 Apps / Office 2024 with all security updates applied

  1. Navigate to Microsoft Update or open any Office application and go to File > Account > Update Options > Update Now
  2. Ensure Microsoft Office is updated to the latest available version for your subscription or perpetual license
  3. For Office LTSC 2021 and Office 2024, apply the latest monthly security updates via Windows Update or the Office Deployment Tool
  4. Verify the installed version by going to File > Account in any Office app and confirm it matches or exceeds the latest released version
Caveat Standard update - minimal risk; ensure backup of critical documents before major version updates

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
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,800.

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-2026-40363 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