CVE-2026-55899
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 · uneditedStack-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
In the news
Third-party coverage- Microsoft July 2026 Patch Tuesday fixes massive 570 flaws, 3 zero-days
- Microsoft CVE Summary - Bleeping Computer
Surfaced from public web coverage — external links open in a new tab.
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 confidenceA stack-based buffer overflow vulnerability exists in Microsoft Office Excel that allows an unauthorized local attacker to execute arbitrary code. The overflow occurs when Excel processes malformed data, causing memory corruption on the stack that can be leveraged to gain code execution privileges.
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 dataall versions= 2016all versionsall versionsall versionsall versions< 16.0.10417.20175CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Verify Microsoft Excel is installedCheck for Excel executable. On Windows, open Command Prompt and run: dir "C:\Program Files\Microsoft Office\root\Office*\EXCEL.EXE" /s 2>nul OR dir "C:\Program Files (x86)\Microsoft Office\root\Office*\EXCEL.EXE" /s 2>nul. Also check registry at HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\EXCEL.EXEAffected if Excel executable is not found on the system - not affected
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Obtain installed Excel version numberOpen Command Prompt and run: excel --version (if available) OR right-click EXCEL.EXE, select Properties, view File Version. For Office Click-to-run, run: officec2rclient.exe /displayuserversion. Alternatively, open Excel, go to File > Account > About ExcelAffected if Cannot determine version - manual review required
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Compare version against affected rangesReview the detected version against: Microsoft 365 Apps (all versions), Excel 2016 (all versions), Office 2019/2021/2024 (all versions), Office Online Server (versions prior to 16.0.10417.20175). For Office Online Server, check version via: Get-OfficeWebAppsServer or review installer log filesAffected if Version falls within any affected range (which includes essentially all current versions of Excel) - likely affected
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Verify Excel is accessible to usersCheck local user access. Run: net localgroup "Users" or review which accounts have logon rights. Check Excel application permissions via: icacls "C:\Program Files\Microsoft Office\root\Office*\EXCEL.EXE"Affected if Non-privileged or untrusted users have access to run Excel - attack surface exists
If Excel is installed and accessible to users on the system, and the version matches the affected product range (which includes virtually all current Excel versions), the environment is likely affected by this vulnerability.
Generated from the published advisory. Verify against your own configuration.
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.
From vendor data16.0.10417.20175
Apply Microsoft security updates for Office Excel as they become available. Restrict local access to trusted users and employ defense-in-depth measures such as endpoint protection and least-privilege user accounts.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-55899 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-55899 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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