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Office Online Server OOS Office Online Server Security update
Patch Tuesday

KB5002855

KB5002855: Cumulative update for Office Online Server, version OOS, April 2026. Excel flaws that could run code or expose information fixed

In short

The update fixes five Important vulnerabilities, including Excel flaws that could let attackers run code or expose information. Office Online Server updates end for all editions on December 31, 2026.

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

Build
16.0.10417.20113
Security
5 fixed
Restart
Required

What changes

Fixes 2 changes

Excel

Verified in package 2 items
  • A flaw in Excel could let an attacker run code on the server.1
    Addresses a Microsoft Excel remote code execution vulnerability.
  • A flaw in Excel could expose information.1
    Addresses a Microsoft Excel Information Disclosure vulnerability.

Technical details

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

Data sheet

Released
2026-04-14
Classification
Security Updates
Type
Cumulative update
Restart
Required
Replaces
KB5002846, KB5002835, KB5002824, KB5002817
+14 earlier KB5002801, KB5002797, KB5002776, KB5002752, KB5002740, KB5002728, KB5002707, KB5002699, KB5002690, KB5002679, KB5002677, KB5002648, KB5002601, KB5002503
Replaced by
KB5002871
VersionBuildChannel
OOS 16.0.10417.20113 General availability

Security

5 vulnerabilities fixed
5 important
VulnerabilitySeverityCVSS
CVE-2026-32189
Microsoft Excel Remote Code Execution Vulnerability
 Important 7.8
CVE-2026-32197
Microsoft Excel Remote Code Execution Vulnerability
 Important 7.8
CVE-2026-32198
Microsoft Excel Remote Code Execution Vulnerability
 Important 7.8
CVE-2026-32199
Microsoft Excel Remote Code Execution Vulnerability
 Important 7.8
CVE-2026-32188
Microsoft Excel Information Disclosure Vulnerability
 Important 7.1

Downloads (Microsoft Update Catalog)

Package OOS
1.0 GB
wacserver-x-none.cab Main update · KB5002855 SHA-1: bb767f88…b6cc55

Updated components

1,583 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 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