September 2025 SharePoint 2016 CU - Configuration Wizard failed

[Applies to SharePoint 2016; not tested on other versions of SharePoint]

While the farm account is in the local admins group (regardless of being present in the WSS_WPG group), running the psconfigui.exe (SharePoint Configuration Wizard) or psconfig.exe with the farm account gets stuck at the last step (step 10 of 10). Associated behaviors are:

  • CopySideBySideFiles_*.log showing the endless repetition of: “\16\TEMPLATE\LAYOUTS\accessrequestcontrol.debug.js Access is denied. Waiting 30 seconds… Retrying…”.
  • Unable to close the Config Wizard by hitting the Cancel or X button on the GUI; it has to be killed in Task Manager.
  • The “Upgrade Status” page on Central Admin, however, shows the green status “Succeeded” even though it's not.

Diagnosis

Microsoft has deployed the security hardening with the 2025 September CU. The farm service account can no longer be used interactively from now on. Previously, this was not a requirement, despite the documentation at https://learn.microsoft.com/en-us/sharepoint/security-for-sharepoint-server/plan-for-administrative-and-service-accounts:


Remedy
 
Ensure your farm admin user account has the rights as specified by the MS documentation (URL above) and use that account, not the farm service account, to run the psconfig (or psconfigui/Config Wizard). Having the farm service account in the local admins group will not prevent you from running the psconfig successfully, but it still needs to be removed for security reasons. 

Note:

If you create any new database using your farm admin user account with PowerShell, your account will become the owner of the database:



This may interfere with some PowerShell-based database operations in future unless permission settings are tightly configured on the SQL and server sides. However, if you create a new content database from Central Admin (caUrl/_admin/cntdbadm.aspx), the farm service account becomes the owner of the database and will cause no issue down the road. More to come on this topic later...


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