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Office Online Server OOS Office Online Server Security update
Patch Tuesday

KB5002871

KB5002871: Cumulative update for Office Online Server, version OOS, May 2026. Excel code execution and information disclosure flaws fixed

In short

Resolves three Important Excel vulnerabilities, including remote code execution and information disclosure flaws.

Does it affect you? Applies to: Servers running the release version of Office Online Server. The update package is for x64 systems.

Build
16.0.10417.20128
Security
3 fixed
Restart
Required

What changes

Fix 1 change

Microsoft Excel

Verified in package

For: Office Online Server administrators

  • Excel remote code execution and information disclosure vulnerabilities are resolved.1
    The update resolves three Important vulnerabilities in Microsoft Excel.

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released
2026-05-12
Classification
Security Updates
Type
Cumulative update
Restart
Required
Replaces
KB5002855, KB5002846, KB5002835, KB5002824
+15 earlier KB5002817, KB5002801, KB5002797, KB5002776, KB5002752, KB5002740, KB5002728, KB5002707, KB5002699, KB5002690, KB5002679, KB5002677, KB5002648, KB5002601, KB5002503
Replaced by
KB5002875
VersionBuildChannel
OOS 16.0.10417.20128 General availability

Security

3 vulnerabilities fixed
3 important
VulnerabilitySeverityCVSS
CVE-2026-40359
Microsoft Excel Remote Code Execution Vulnerability
 Important 7.8
CVE-2026-40360
Microsoft Excel Information Disclosure Vulnerability
 Important 7.8
CVE-2026-40362
Microsoft Excel Remote Code Execution Vulnerability
 Important 7.8

Downloads (Microsoft Update Catalog)

Package OOS
1.0 GB
wacserver-x-none.cab Main update · KB5002871 SHA-1: de6d58b5…979b20

Updated components

1,578 files changed since the previous update for the same versions.

Top changed componentsFiles
Office web apps367
PowerPoint322
Excel260
Document conversion74
Word50

Verified in package: changed files confirm Microsoft Excel.

Sources

Updated
Cited passages from Microsoft's official notes (1)
  1. 1. This security update resolves Microsoft Excel remote code execution vulnerability and Microsoft Excel Information Disclosure vulnerability. support.microsoft.com
Checked automatically: 8 of 8 checks passed, 1 quoted passage · compared with Microsoft's page on Sep 26, 2026
  • Quotes found in the official pages: passed
  • Numbers found in the sources: passed
  • Vulnerabilities from the dossier only: passed
  • Links to allowed domains only: passed
  • Every official change covered: passed
  • Readable plain text: passed
  • Changes confirmed by the file list: passed
  • Sources agree: passed

A second AI read the text against the sources: correctness 5/5, clarity 4/5, completeness 5/5. How we work

Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake