CVE-2026-55138
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 · uneditedUntrusted pointer dereference in Microsoft Office Excel allows an unauthorized attacker to disclose information 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 confidenceThis is a memory safety vulnerability in Microsoft Office Excel where an untrusted pointer dereference allows a local unauthorized attacker to read arbitrary memory locations, potentially exposing sensitive information. The flaw does not require authentication and is exploited through a specially crafted file or operation within 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 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
- None
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
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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Determine installed Excel versionOpen Excel, go to File > Account > About Excel, or run 'winword --version' or 'excel --version' from command line, or check HKLM\SOFTWARE\Microsoft\Office\ClickToRun\Configuration in registryAffected if version is Microsoft Excel 2016 or later, or part of Microsoft 365 Apps, Office 2019, Office 2021, Office 2024, or Office Online Server versions below 16.0.10417.20175
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Check Office Online Server versionIf using Office Online Server, run 'Get-OfficeOnlineServerHealthReport' or check the installed version via Programs and Features, looking for version 16.0.10417.20175 or higherAffected if Office Online Server version is below 16.0.10417.20175
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Verify Excel file handling exposureConfirm that Excel is configured to open files from untrusted sources without Protected View enabled. Check via File > Options > Trust Center > Trust Center Settings > Protected ViewAffected if Protected View is disabled and users can open Excel files from untrusted or unknown sources directly
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Confirm lack of specific security updateCheck Windows Update history or patch management system for installation of Microsoft security updates addressing CVE-2026-55138 for Office/ExcelAffected if no security update specifically addressing CVE-2026-55138 has been installed
User is affected if running any Microsoft Excel version 2016 or later, or Microsoft 365/Office 2019/2021/2024/2025, or Office Online Server below version 16.0.10417.20175, without the CVE-2026-55138 security update applied.
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. Until the patch is released, exercise caution with files from untrusted sources and consider enabling Protected View in Excel to mitigate risks.
- Consultation1.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-55138 — 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-2026-55138 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
- No spam, self-promotion, credentials, or personal data