Windows 10 October 2021 cumulative update preview: KB5006738/19043(4).1320 #KBAlert #WinTen21H2


Hi all,

Before getting into what’s changed in today’s cumulative update preview (optional update), a few important things:

  1. Windows 10 Version 21H2 now has a name: November 2021 Update.
  2. Starting from this KB alert, Windows 10 Version 21H2 release notes will be published, hence build 19043(4) in the subject line (Version 21H2 is build 19044). Note that build 19044 is going through final testing before going out to everyone soon.
  3. A new hashtag, #WinTen21H2 will be reserved for Windows 10 21H2 discussion.
  4. As usual, whenever a feature update is released for Windows 10 (and next year, Windows 11), cumulative update notices for the immediate past update will be sent here for about 60 days. Therefore KB alert posts will mention Version 21H1 (build 19043/May 2021 Update) for about 60 days after release of Windows 10 21H2 in November, so until January 2022 at the earliest.
  5. As noted previously, Windows 10 November 2021 Update (build 19044) will work with screen readers compatible with Version 21H1.
  6. I will mention this again in November, but for smoother experience when upgrading to Windows 10 21H2, please upgrade to at least Windows 10 21H1. This is more so now for Version 2004 (May 2020 Update/build 19041) users as it is going out of support this December.


With that out of the way:

October 2021 optional cumulative update for Windows 10 (KB5006738/build 19043(4).1320) is now available from Windows Update:

October 26, 2021—KB5006738 (OS Builds 19041.1320, 19042.1320, and 19043.1320) Preview (



Updates an issue an issue that might prevent subtitles from displaying for certain video apps and streaming video sites. 

Updates an issue that prevents Kana input mode users from inserting a question mark (?) using the Shift-0 key combination.

Updates an issue that sometimes causes your lock screen background to appear black if you have set up a slideshow of pictures as your lock screen background. 




Version 21H1 (19043.1320):

Addresses an issue that prevents you from accessing the pre-provisioning page during the out-of-box experience (OOBE). This issue occurs when the credentials page for signing in to Azure Active Directory appears, and you press the Windows key five times.

Adds a feature that facilitates certain cross-browser data transfers.

Addresses an issue with Assigned Access kiosks that are configured with Microsoft Edge as a kiosk application. These kiosks might sometimes fail to restart Microsoft Edge if users close the browser window.

Addresses an issue in which the use of App-V intermittently causes black screens to appear when signing in on the credentials page.

Addresses an issue that might prevent subtitles from displaying for certain video apps and streaming video sites.

Addresses an issue that prevents Windows 10 virtual private network (VPN) users from connecting to Windows Server 2019 Routing and Remote Access service (RRAS) servers.

Addresses an issue that prevents Software-Defined Networking (SDN) virtual machines from working when you configure the Generic Routing Encapsulation (GRE) VPN bandwidth limitation.

Addresses a Primary Refresh Token (PRT) update issue that occurs when VPN users sign in using Windows Hello for Business when the VPN connection is offline. Users receive unexpected authentication prompts for online resources that are configured for user sign-in frequency (SIF) in Azure Active Directory-Conditional Access.

Addresses an issue that causes Windows to go into BitLocker recovery after a servicing update.

Addresses an issue that might cause Kerberos.dll to stop working within the Local Security Authority Subsystem Service (LSASS). This occurs when LSASS processes simultaneous Service for User (S4U) user-to-user (U2U) requests for the same client user.

Addresses an issue in Code Integrity that might cause a memory leak.

Enhances Microsoft Defender for Endpoint’s ability to identify and intercept ransomware and advanced attacks.

Addresses an issue in the OOBE that might cause Windows AutoPilot provisioning to fail.

Addresses an issue that prevents Kana input mode users from inserting a question mark (?) using the Shift-0 key combination.

Addresses an issue that sometimes causes the lock screen to appear black if you set up slideshow.

Addresses a reliability issue with LogonUI.exe, which affects the rendering of the network status text on the credentials screen.

Addresses an issue that causes Server Message Block (SMB) Query Directory Requests to fail when the buffer size is large.

Addresses a memory leak issue in lsass.exe on domain controllers in the forest root domain that occurs when you have multiple forests and multiple domains in each forest. The SID-Name mapping functions leak memory when a request comes from another domain in the forest and crosses forest boundaries.

Addresses an issue with the virtual machine (VM) Load Balancing feature, which ignores a site’s fault domain.

Addresses a known issue that might prevent the successful installation of printers using the Internet Printing Protocol (IPP).


Version 21H2 preview (19044.1320): same as 21H1.




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