Microsoft Defender Application Control and the unwanted reboot

I came across this issue again this week on a customer site. Windows 10 computers were being rebooted without warning. 

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I narrowed this down to Microsoft Defender Application Control in Microsoft Endpoint Manager, "Application control code integrity policies" being set, even to Audit Only. 

This is created as a Windows 10 configuration profile, choosing the Endpoint Protection template, then selecting the Microsoft Defender Application Control.

If you use the tooltip and follow the "Learn more" link, you are directed to the Applocker CSP page, so clearly that's what is in use here. 

According to the Microsoft docs, prior to Windows 10 version 1709, Windows Defender Application Control was known as configurable code integrity (CCI). Interestingly, this is the only AppLocker setting that causes a reboot. It's well documented on the Applocker CSP page. 

"The AppLocker CSP will schedule a reboot when a policy is applied or a deletion occurs using the AppLocker/ApplicationLaunchRestrictions/Grouping/CodeIntegrity/Policy URI".

I can verify that the reboot occurs when you apply the policy but also when you remove it.

Some of my colleagues have suggested ways to avoid the reboot. 

• Peter van der Woude talks about creating a custom code integrity policy using OMA-URI and the Application Control CSP.
• Rudy Ooms talks about the WDAC wizard.
  
• You can read about creating a new base policy in the official docs using the WDAC wizard. 

This reboot is not a problem when you configure the same setting with ConfigMgr.

In ConfigMgr, the WDAC wizard allows us to de-select the check box to enforce the required reboot.

I hope this helps.

Until next time.......

Software updates issue - access denied

We encountered this problem recently on a customer site. The customer uses ConfigMgr to patch their Windows 10 estate. They've not had any major issues for quite some time but then the January CU for Windows 10 v1909 (KB5009545) started to fail with the Access is denied error (0x80070005).

We could see the error in the UpdatesHandler.log file.

WSUS update (92c58401-7a51-4e9d-9457-ca1a93c3e3d9) installation result = 0x80070005, Reboot State = NoReboot

Update execution failed.

But what did that mean? Nothing had changed so why all of a sudden was access denied? What specifically was being denied access?

We found the answer in the CBS.log file. CBS refers to Component-Based Servicing. Some components might be installed or uninstalled during Windows updates, and CBS.log is a file that includes details of these components. This file logs detailed information from your most recent Windows installed updates, and thus it can be used for troubleshooting issues related to your updates.

This log file is located in %windir%\Logs\CBS\ folder. There were several errors like this repeating over and over

2022-02-08 19:32:05, Info                  DPX    DpxMoveFileExW failed, source: \\?\C:\Windows\SoftwareDistribution\Download\55d2d88ec6c8540e1de4d959136d1809\inst\_Windows10.0-KB5009545-x64.cab_\$dpx$.tmp\4f76f8be37b84846a53e298df591e679.tmp, destination: \\?\C:\Windows\SoftwareDistribution\Download\55d2d88ec6c8540e1de4d959136d1809\inst\_Windows10.0-KB5009545-x64.cab_\amd64_microsoft-windows-e..-unifiedwritefilter_31bf3856ad364e35_10.0.18362.449_none_f216a3681960d832\r\uwfservicingscr.scr, hr 0x80070005

We could see similar issues using Procmon

8:51:31.2419935 PM  TiWorker.exe  10516  SetRenameInformationFile C:\Windows\SoftwareDistribution\Download\7998dad7da209654d66a9b53acb8a555\inst\_Windows10.0-KB5010345-x64.cab_\$dpx$.tmp\8bdd9ac34e21374c8fe95160faa8a43e.tmp        ACCESS DENIED            ReplaceIfExists: True, FileName: C:\Windows\SoftwareDistribution\Download\7998dad7da209654d66a9b53acb8a555\inst\_Windows10.0-KB5010345-x64.cab_\x86_microsoft-windows-photoscreensaver_31bf3856ad364e35_10.0.18362.1316_none_1d493b2302fc0b6b\r\photoscreensaver.scr

This error referred to TiWorker.exe which is the TrustedInstaller process and suggested that it did not have Full Control or Full Access to all the folders or sub-folders within the directory named SoftwareDistribution (C:\Windows\SoftwareDistribution). This didn't make much sense as nothing had changed in the environment.

We noticed that all the files that were blocked had a .SCR extension. These were screensaver files that were being updated by the January CU. Then we discovered that there was a McAfee access protection rule in place to block access to .SCR files. 

The fix was then straightforward. We excluded the TiWorker.exe process from the Block all SCR rule and the updates started to install.

I hope this helps if you find yourself in a similar situation. CBS logs and Procmon are your friends 😀

Until next time........