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Windows 10 1809 Windows 10 1809 Out-of-band update
Out-of-band

KB5091573

KB5091573: Cumulative update for Windows 10, version 1809, April 2026. Secure Boot certificates face expiration; Azure checks updated

In short

Includes updated Azure-hosted device certificate checks. Microsoft also warns that Secure Boot certificates have started expiring and recommends preparing in advance.

Does it affect you? Applies to: The page lists Windows 10, version 1809 Enterprise LTSC 2019 under Applies to, but also says this out-of-band update applies to Windows Server 2019 only. The page does not resolve this inconsistency.

Build
17763.8647
Restart
Required

Microsoft publishes separate notes for this KB for Windows Server.

What changes

Improvement 1 change

Servicing stack update (SSU)

For: Azure-hosted devices

  • The included SSU improves checks that determine whether a device is hosted on Azure.1
    The SSU uses an updated certificate chain for Azure-hosting validation. Azure-hosted devices need access to the required certificate-update domains to download and install certificate updates.

Technical details

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

Data sheet

Released
2026-04-19
Classification
Updates
Type
Cumulative update
Restart
Required
Replaces
KB5082123, KB5078752, KB5075904, KB5078131
+17 earlier KB5077795, KB5073723, KB5074975, KB5071544, KB5068791, KB5066586, KB5065428, KB5066187, KB5063877, KB5062557, KB5060531, KB5061978, KB5058392, KB5059091, KB5058922, KB5050008, KB5037425
Replaced by
KB5087538
VersionBuildChannel
1809 17763.8647 General availability

Security

No vulnerabilities are listed for this update.

Updated components

31 files changed since the previous update for the same versions.

Top changed componentsFiles
Secure Boot6
Remote Desktop4
Security and sign-in2

Sources

Updated
Cited passages from Microsoft's official notes (1)
  1. 1. This servicing stack update (SSU) includes enhanced logic to verify whether a device is hosted on Azure, leveraging an updated certificate chain for validation. support.microsoft.com
Checked automatically: 8 of 8 checks passed, 1 quoted passage · compared with Microsoft's page on Sep 25, 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 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