Skip to the content
The Update Bureau
Exchange Server 2019 CU14 Exchange Server 2019 CU14 ESU only Security update
Patch Tuesday

KB5074994

KB5074994: Security update for Exchange Server 2019 CU14, February 2026. Spoofing flaw needs a separate mitigation step

In short

The update addresses a spoofing vulnerability in Exchange Server, but the CVE bulletin's mitigation instructions are also needed. Only organizations enrolled in the Extended Security Update program are eligible.

Does it affect you? Applies to: This update is for Exchange Server 2019 CU14 (build 15.2.1544.39). Only organizations enrolled in the Extended Security Update (ESU) program are eligible to receive it.

Build
15.2.1544.39
Servicing branch
CU14
Security
1 fixed
Review notes Additional details from the official release notes (1) Read note
  • What changes KB5074994 was superseded by KB5094142 on 2026-09-26.

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

Fix 1 change

Microsoft Exchange Server

  • The update resolves a spoofing vulnerability, but mitigating it also requires following the instructions in the CVE bulletin.1
    CVE-2026-21527.

Improvement 1 change

Update replacement

  • This update replaces the December 9, 2025 security update, KB5071874.2

Technical details

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

Data sheet

Released
2026-02-10
Classification
Security Updates
Type
Cumulative update
Servicing branch
CU14
Replaces
KB5071874
Replaced by
KB5094142
VersionBuildChannel
2019 15.2.1544.39 General availability

Security

1 vulnerability fixed
1 important
VulnerabilitySeverityCVSS
CVE-2026-21527
Microsoft Exchange Server Spoofing Vulnerability
 Important 6.5

Updated components

1,012 files changed since the previous update for the same versions.

Top changed componentsFiles
Management and PowerShell134
Transport93
Client access (POP, IMAP, ActiveSync)33
Mailbox replication33
Search27
Compliance and eDiscovery25
Exchange Web Services and Autodiscover17
Outlook on the web8
Setup8

Sources

Updated
Cited passages from Microsoft's official notes (2)
  1. 1. This security update resolves vulnerabilities in Microsoft Exchange Server. support.microsoft.com
  2. 2. This security update replaces the following previously released updates: Description of the security update for Microsoft Exchange Server 2019 CU14: December 9, 2025 (KB5071874) support.microsoft.com
Checked automatically: 8 of 8 checks passed, 2 quoted passages · 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 5/5, 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