Intune, WDAC and Managed Installer

WDAC has an option (Option 13) to allow apps installed by a Managed Installer. This sounds great! Everything you install using your preferred installer would be allowed, without going to the trouble of creating rules. But there’s a snag. There is no Configuration Service Provider (CSP) to deliver this policy in Intune.

The Managed Installer option actually uses the same method to allow executables to run as the Intelligent Security Graph option (Option 14). When a file is authorised by one of these methods, an extended attribute is written to the file. You can see this attribute with the fsutil utility. The method is documented here: Automatically allow apps deployed by a managed installer with Windows Defender Application Control.

The documentation on Managed Installer is a little confusing. The main documentation shows a policy that allows the Intune Management Extension, as well as the SCCM extension.

<FilePublisherRule Id="55932f09-04b8-44ec-8e2d-3fc736500c56" Name="MICROSOFT.MANAGEMENT.SERVICES.INTUNEWINDOWSAGENT.EXE version or greater in MICROSOFT® INTUNE™ from O=MICROSOFT CORPORATION, L=REDMOND, S=WASHINGTON, C=US" Description="" UserOrGroupSid="S-1-1-0" Action="Allow"> <Conditions> <FilePublisherCondition PublisherName="O=MICROSOFT CORPORATION, L=REDMOND, S=WASHINGTON, C=US" ProductName="*" BinaryName="MICROSOFT.MANAGEMENT.SERVICES.INTUNEWINDOWSAGENT.EXE"> <BinaryVersionRange LowSection="" HighSection="*" /> </FilePublisherCondition> </Conditions> </FilePublisherRule>

So, looking at that, we would obviously be able to allow Intune apps in Intune, right? But we cannot. The reason is that the documentation also describes implementing this policy in a GPO. But in Intune we cannot use GPO’s and, instead, we use Configuration Service Providers (CSP). The Managed Installer option is implemented as an AppLocker policy, and the AppLocker CSP does not contain a section for the Managed Installer rule collection type.

Although we cannot implement this as an Intune policy (because there is no CSP), we could theoretically implement it another way. With a registry key, for example, even if there were no CSP to configure the registry key, we could simply add, change or delete it in script. With AppLocker policies, we can use PowerShell to create a policy from an XML file, using Set-AppLockerPolicy. So the solution is to deliver a custom AppLocker policy with PowerShell, to enable the Intune agent as a Managed Installer in WDAC.

There are three significant drawbacks:

  1. The effort and constraints in managing the policies manually through PowerShell. For example, there is no Remove cmdlet for a policy in PowerShell
  2. Managed Installer tags the installed files, but not automatic updates. To allow the updates, you would either have to reinstall, or apply rules to allow the updated files, which would defeat the purpose.

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