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365 AppsApplication · Microsoft

CVE-2026-20950

HIGH · 7.8 CVSS v3.1 Published 2026-01-13
Fix available
A fix is available. Upgrade to 16.0.10417.20083 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 it has been freed, allowing an unauthorized attacker to execute arbitrary code locally on the affected system.

MitigationApply the latest Microsoft Office security updates to patch the use-after-free vulnerability in Excel.

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:< 16.0.10417.20083

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. Check installed Excel version on Windows
    Open Excel, go to File > Account > About Excel, or run 'excel --version' from Command Prompt, or check Registry key: HKEY_CURRENT_USER\Software\Microsoft\Office\ClickToRun\Configuration or HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun\Configuration for Microsoft 365/Office 365 installs
    Affected if Version is 2016 or later, or the product is Microsoft 365 Apps (any version)
  2. Check installed Microsoft Office suite version
    Open any Office app (Word, Excel, etc.), go to File > Account > About [App], or check Registry under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun\Configuration for the OfficeSwVersion value
    Affected if Version is 2019 or later, or 2021, or 2024 (LTSC)
  3. Check Microsoft Office Online Server version
    On the server, open Windows Explorer, navigate to C:\Program Files\Microsoft Office Web Servers\OfficeWS\, right-click on the ExcelService.dll file, select Properties, and view the File Version in the Details tab
    Affected if Version is below 16.0.10417.20083
  4. Verify vulnerability trigger condition
    This use-after-free vulnerability is triggered when opening a specially crafted malicious Excel file (.xlsx, .xlsm, .xlsb). No specific feature or add-in needs to be enabled for exploitation.
    Affected if User opens a malicious Excel file received via email, download, or other means

Your environment is affected if you run any supported version of Microsoft Excel (2016+), Microsoft Office (2019+), Microsoft 365 Apps, or Office Online Server versions below 16.0.10417.20083, as all of these are within the affected ranges.

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 16.0.10417.20083 or later
Fixed in 16.0.10417.20083
Interim mitigation

Apply the latest Microsoft Office security updates to patch the use-after-free vulnerability in Excel.

Recommended fix Moderate confidence

Latest Microsoft 365/Office updates (check File > Account > Update Options for version info); Office Online Server: 16.0.10417.20083 or later

  1. 1. Open Microsoft Excel or any Office application
  2. 2. Go to File > Account
  3. 3. Click on 'Update Options'
  4. 4. Select 'Update Now' to download and install the latest security updates
  5. 5. Alternatively, check for Windows Updates via Start > Settings > Update & Security > Windows Update
  6. 6. Ensure all pending Microsoft Office updates are installed
  7. 7. Restart Excel and verify the application runs without errors after updating
Caveat Minimal risk - Microsoft security updates typically have no breaking changes; ensure backups of critical Excel files exist before major version upgrades

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
  • Implementation3.0 h
  • Testing4.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,720
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,752.

Scan for this in your stack

Free · runs locally
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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-2026-20950 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