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Exchange Server 2019 CU14 Exchange Server 2019 CU14 ESU only Security update
Patch Tuesday Zero-day

KB5094142

KB5094142: Security update for Exchange Server 2019 CU14, June 2026. Actively exploited spoofing flaw; mitigation services error fixed

In short

The update addresses seven of the eight listed vulnerabilities, including the critical, actively exploited Exchange spoofing flaw; it does not include the fix for CVE-2026-45583. It also fixes an “Unknown Issuer” error in mitigation and flighting services.

Does it affect you? Applies to: Organizations enrolled in the Extended Security Update (ESU) program that run Exchange Server 2019 CU14. Exchange Server 2019 is out of support, and organizations outside ESU are not eligible for these updates.

Build
15.2.1544.41
Servicing branch
CU14
Security
8 fixed · 1 critical · 1 exploited

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

Exchange mitigation and flighting services

  • Exchange mitigation and flighting services no longer fail with an “Unknown Issuer” error.1

Technical details

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

Data sheet

Released
2026-06-09
Classification
Security Updates
Type
Cumulative update
Servicing branch
CU14
Replaces
KB5074994
Replaced by
KB5103214
VersionBuildChannel
2019 15.2.1544.41 General availability

Security

8 vulnerabilities fixed
1 exploited 1 critical 7 not rated
VulnerabilitySeverityCVSS
CVE-2026-42897 Exploited
Microsoft Exchange Server Spoofing Vulnerability
 Critical 8.1
CVE-2026-45500
Microsoft Exchange Server Spoofing Vulnerability
 Not rated —
CVE-2026-45501
Microsoft Exchange Server Spoofing Vulnerability
 Not rated —
CVE-2026-45502
Microsoft Exchange Server Information Disclosure Vulnerability
 Not rated —
CVE-2026-45503
Microsoft Exchange Server Information Disclosure Vulnerability
 Not rated —
CVE-2026-45504
Microsoft Exchange Server Elevation of Privilege Vulnerability
 Not rated —
CVE-2026-45583
Microsoft Exchange Server Remote Code Execution Vulnerability
 Not rated —
CVE-2026-47631
Microsoft Exchange Server Spoofing Vulnerability
 Not rated —

Updated components

1,276 files changed since the previous update for the same versions.

Top changed componentsFiles
Management and PowerShell155
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 (1)
  1. 1. Exchange mitigation and flighting services fail due to "Unknown Issuer" error 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 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