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Exchange Server 2019 CU14 Exchange Server 2019 CU14 ESU only Security update
Patch Tuesday Final update for this version

KB5128897

KB5128897: Security update for Exchange Server 2019 CU14, October 2026. Remote-code-execution flaw patched; published calendar errors fixed

In short

Addresses six Exchange Server vulnerabilities, including one critical flaw, and resolves HTTP 500 errors affecting published calendar subscriptions. It is available only to organizations enrolled in the Extended Security Update program.

Does it affect you? Applies to: Exchange Server 2019 CU14 organizations enrolled in the Period 2 Extended Security Update (ESU) program. This update installs build 15.2.1544.50.

Build
15.2.1544.50
Servicing branch
CU14
Security
6 fixed · 1 critical

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

  • The update addresses six security vulnerabilities, including one critical remote-code-execution flaw.1
    Addresses CVE-2026-70571 (remote code execution); CVE-2026-77910, CVE-2026-87692, CVE-2026-87695, and CVE-2026-87696 (elevation of privilege); and CVE-2026-70279 (spoofing).

Published calendars (.ics)

  • Published calendar subscriptions that return HTTP 500 are resolved by this update.2
    The linked resolution article lists KB5128897 as a resolving update. The reported symptoms followed the August 2026 security update for Exchange Server Subscription Edition, build 15.2.2562.46.

Technical details

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

Data sheet

Released
2026-10-13
Classification
Security Updates
Type
Cumulative update
Servicing branch
CU14
Replaces
KB5129957
VersionBuildChannel
2019 15.2.1544.50 General availability

Security

6 vulnerabilities fixed
1 critical 5 important
VulnerabilitySeverityCVSS
CVE-2026-70571
Microsoft Exchange Server Remote Code Execution Vulnerability
 Critical 8.1
CVE-2026-70279
Microsoft Exchange Server Spoofing Vulnerability
 Important 9.3
CVE-2026-77910
Microsoft Exchange Server Elevation of Privilege Vulnerability
 Important 8.8
CVE-2026-87692
Microsoft Exchange Server Elevation of Privilege Vulnerability
 Important 7.8
CVE-2026-87695
Microsoft Exchange Server Elevation of Privilege Vulnerability
 Important 7.8
CVE-2026-87696
Microsoft Exchange Server Elevation of Privilege Vulnerability
 Important 7.5

Updated components

1,007 files changed since the previous update for the same versions.

Top changed componentsFiles
Management and PowerShell123
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 (2)
  1. 1. This security update resolves vulnerabilities in Microsoft Exchange Server. support.microsoft.com
  2. 2. Description of the security update for Microsoft Exchange Server 2019 CU14 October 13, 2026 (KB5128897) support.microsoft.com
Checked automatically: 8 of 8 checks passed, 2 quoted passages · 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