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Exchange Server 2019 CU14 Exchange Server 2019 CU14 ESU only Security update
Patch Tuesday

KB5071874

KB5071874: Security update for Exchange Server 2019 CU14, December 2025. Exchange privilege escalation and spoofing flaws addressed

In short

Addresses two important Exchange Server vulnerabilities: one involving privilege escalation and one involving spoofing. Only organizations enrolled in the Extended Security Update program are eligible.

Does it affect you? Applies to: Exchange Server 2019 CU14 systems at organizations enrolled in the Extended Security Update program. Exchange Server 2019 has reached end of support.

Build
15.2.1544.37
Servicing branch
CU14
Security
2 fixed
Review notes Additional details from the official release notes (1) Read note
  • In detail Exchange Server 2019 ESU security updates are scheduled to end on October 31, 2026.

The official sources are linked at the end of the page.

For servers running Cumulative Update 14: each cumulative update gets its own update. Support for this version ended on October 14, 2025: Microsoft releases this update only to organizations enrolled in the Extended Security Update (ESU) program, not through Microsoft Update. The others should move to Exchange Server Subscription Edition. Which version am I on?

What changes

Fixes 2 changes

Exchange Server

2 items
  • An Exchange Server elevation-of-privilege vulnerability is addressed.1
    CVE-2025-64666.
  • An Exchange Server spoofing vulnerability is addressed.1
    CVE-2025-64667.

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
CU14
Replaces
KB5066368
Replaced by
KB5074994
VersionBuildChannel
2019 15.2.1544.37 General availability

Security

2 vulnerabilities fixed
2 important
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

Updated components

1,017 files changed since the previous update for the same versions.

Top changed componentsFiles
Management and PowerShell129
Transport93
Client access (POP, IMAP, ActiveSync)33
Mailbox replication33
Search27
Compliance and eDiscovery26
Exchange Web Services and Autodiscover17
Outlook on the web8
Setup8

Sources

Updated
Cited passages from Microsoft's official notes (1)
  1. 1. - CVE-2025-64666 - Microsoft Exchange Server Elevation of Privilege Vulnerability - CVE-2025-64667 - Microsoft Exchange Server Spoofing Vulnerability support.microsoft.com
Checked automatically: 8 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: passed

A second AI read the text against the sources: correctness 5/5, 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