Skip to the content
The Update Bureau
Exchange Server Subscription Edition RTM Exchange Server Subscription Edition RTM Security update
Patch Tuesday

KB5071876

KB5071876: Security update for Exchange Server Subscription Edition RTM, December 2025. Exchange privilege and spoofing flaws addressed; OWA integration fixed

In short

Addresses three Exchange Server vulnerabilities and fixes a Skype for Business integration failure in Outlook on the web.

Does it affect you? Applies to: Exchange Server Subscription Edition RTM servers. The update package is for x64 and updates the server to build 15.2.2562.35.

Build
15.2.2562.35
Servicing branch
RTM
Security
3 fixed
Restart
Required

What changes

Fix 1 change

Outlook on the web

Verified in package
  • Skype for Business integration with Outlook on the web works after enabling the Dedicated Hybrid Application.1

Technical details

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

Data sheet

Released
2025-12-09
Classification
Security Updates
Type
Cumulative update
Servicing branch
RTM
Restart
Required
Replaces
KB5066366, KB5066373
Replaced by
KB5074992
VersionBuildChannel
SE 15.2.2562.35 General availability

Security

3 vulnerabilities fixed
2 important 1 not rated
VulnerabilitySeverityCVSS
CVE-2025-64666
Microsoft Exchange Server Elevation of Privilege Vulnerability
 Important 7.5
CVE-2025-64667
Microsoft Exchange Server Spoofing Vulnerability
 Important 5.3
CVE-2025-59249
Microsoft Exchange Server Elevation of Privilege Vulnerability
 Not rated —

Updated components

1,031 files changed since the previous update for the same versions.

Top changed componentsFiles
Management and PowerShell141
Transport93
Client access (POP, IMAP, ActiveSync)33
Mailbox replication33
Search27
Compliance and eDiscovery26
Exchange Web Services and Autodiscover17
Outlook on the web8
Setup8

Verified in package: changed files confirm Outlook on the web.

Sources

Updated
Cited passages from Microsoft's official notes (1)
  1. 1. Skype for Business OWA integration fails after enabling the Dedicated Hybrid Application support.microsoft.com
Checked automatically: 7 of 8 checks passed, 1 quoted passage · compared with Microsoft's page on Oct 20, 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 5/5, clarity 5/5, 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