CVE-2026-55054 in Microsoft Excel and Microsoft 365 Apps
Microsoft Excel has an out-of-bounds read issue that can disclose information when a user opens a crafted file.
Quick answer
Microsoft Excel / Microsoft 365 Apps should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- Microsoft 365 Apps for Enterprise, Excel 2016, Office 2019, Office LTSC 2021/2024, Office for Mac, and Office Online Server versions listed by Microsoft for CVE-2026-55054
Fixed versions
- Apply the July 2026 Microsoft Office security update; Excel 2016 16.0.5561.1001 or later, Office for Mac 16.111.26071215 or later, and Office Online Server 16.0.10417.20175 or later where applicable
How to fix it
Update Microsoft Excel / Microsoft 365 Apps. The old version has a Microsoft security bug that can expose data or raise access.
- Install the latest Microsoft security update for the affected product.
- Restart the app or device if the update asks for it.
- Block use of outdated builds in your software inventory.
- Ask users not to open files or links from unknown sources.
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Verify the fix
- Confirm the installed version matches Apply the July 2026 Microsoft Office security update; Excel 2016 16.0.5561.1001 or later, Office for Mac 16.111.26071215 or later, and Office Online Server 16.0.10417.20175 or later where applicable.
- Run your vulnerability scanner again and confirm this CVE is gone.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-55054?
Microsoft Excel / Microsoft 365 Apps versions listed as affected should be reviewed: Microsoft 365 Apps for Enterprise, Excel 2016, Office 2019, Office LTSC 2021/2024, Office for Mac, and Office Online Server versions listed by Microsoft for CVE-2026-55054.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.