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Office Online Server OOS Office Online Server Security update
Patch Tuesday

KB5002824

KB5002824: Cumulative update for Office Online Server, version OOS, January 2026. Two critical Excel remote-code-execution flaws addressed

In short

The update addresses two critical Excel remote-code-execution vulnerabilities and one other vulnerability. Office Online Server updates for all editions end on December 31, 2026.

Does it affect you? Applies to: Computers running the release version of Office Online Server.

Build
16.0.10417.20083
Security
3 fixed · 2 critical
Restart
Required

What changes

Fix 1 change

Excel

Verified in package

For: Office Online Server administrators

  • A Microsoft Excel remote-code-execution vulnerability is addressed.1

Technical details

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

Data sheet

Released
2026-01-13
Classification
Security Updates
Type
Cumulative update
Restart
Required
Replaces
KB5002817, KB5002801, KB5002797, KB5002776
+11 earlier KB5002752, KB5002740, KB5002728, KB5002707, KB5002699, KB5002690, KB5002679, KB5002677, KB5002648, KB5002601, KB5002503
Replaced by
KB5002835
VersionBuildChannel
OOS 16.0.10417.20083 General availability

Security

3 vulnerabilities fixed
2 critical 1 important
VulnerabilitySeverityCVSS
CVE-2026-20955
Microsoft Excel Remote Code Execution Vulnerability
 Critical 7.8
CVE-2026-20957
Microsoft Excel Remote Code Execution Vulnerability
 Critical 7.8
CVE-2026-20950
Microsoft Excel Remote Code Execution Vulnerability
 Important 7.8

Downloads (Microsoft Update Catalog)

Package OOS
1.0 GB
wacserver-x-none.cab Main update · KB5002824 SHA-1: 3f9b9121…a73099

Updated components

1,597 files changed since the previous update for the same versions.

Top changed componentsFiles
Office web apps369
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. support.microsoft.com
Checked automatically: 7 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: not passed

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