Me and Earl and the Microsoft Store Apps

This blog will be about securing the forgotten Microsoft Store. The Microsoft App Store is ideal for downloading Spotify/Netflix or games on a Company-owned device. Of course, you want to block or limit access.

In my opinion, you will need to start using all the features of the Company Portal and distributing apps with it.

Will you start blocking access to the Microsoft Store, restricting UWP apps that can be installed, or only showing the private Company Microsoft Store? And what about installing App packages manually? How are you going to deal with those packages?

1. Requiring a Private Store

We will begin with the option to only show the private store and nothing more. I guess it’s the most restrictive solution you have.

It only requires a CSP to do so.

./User/Vendor/MSFT/Policy/Config/ApplicationManagement/RequirePrivateStoreOnly

Or if you prefer the Settings Catalog (Duh… of course, you do). Just search Require Private Store Only and enable it.

But beware of the licensing requirements. The RequirePrivateStoreOnly needs a Windows 10 Education or Enterprise edition to function.

Testing it!

When you take a look at the Microsoft Store in Windows 10, you will notice only your Private/Store Company Microsoft Store apps are available.

The same setting in Windows 11 will cause some different behavior because in Windows 11 there is no such thing as a Private store. The Require Private Store device configuration profile will block all access to the Microsoft Store in Windows 11!

2. Limit Applications

If you don’t have the proper licensing but you still want to restrict access to the Microsoft Store, you could configure some Applocker Store App Rules

With Applocker, we can define which UWP apps may be installed from the Microsoft Store

To set up Applocker, you still need to create a custom CSP Rule. Configuring Applocker with the settings catalog isn’t supported.

OMA-URI:

./Vendor/MSFT/AppLocker/ApplicationLaunchRestrictions/StoreAppsGroup/StoreApps/Policy

Content of the XML

<RuleCollection Type="Appx" EnforcementMode="Enabled">
	<FilePublisherRule Id="617edd5b-3360-4281-9724-21e453587fce" Name="Alle ondertekende toepassingspakketten" Description="Hiermee kunnen leden van de groep Iedereen ondertekende toepassingspakketten uitvoeren." UserOrGroupSid="S-1-1-0" Action="Allow">
		<Conditions>
			<FilePublisherCondition PublisherName="CN=MICROSOFT CORPORATION, O=MICROSOFT CORPORATION, L=REDMOND, S=WASHINGTON, C=US" ProductName="*" BinaryName="*"> 
				<BinaryVersionRange LowSection="0.0.0.0" HighSection="*" />
			</FilePublisherCondition>
		</Conditions>
	</FilePublisherRule>
	<FilePublisherRule Id="617edd5b-3360-4281-9724-21e443587fce" Name="Whitelist Microsoft Windows app" Description="" UserOrGroupSid="S-1-1-0" Action="Allow">
		<Conditions>
			<FilePublisherCondition PublisherName="CN=MICROSOFT Windows, O=MICROSOFT CORPORATION, L=REDMOND, S=WASHINGTON, C=US" ProductName="*" BinaryName="*">
				<BinaryVersionRange LowSection="0.0.0.0" HighSection="*" />
			</FilePublisherCondition>
		</Conditions>
	</FilePublisherRule>
</RuleCollection>

Looking at the XML above, you will notice I am using FIlePublisherRules to make sure only Microsoft Apps may be installed. All other Apps will fail to install.

When deploying this Applocker policy to all devices, you could check if the new Applocker policy has been applied by taking a look at this Applocker folder c:\Windows\System32\AppLocker\MDM\

Testing it!

After you are sure the Applocker policy is applied, you can try to download Spotify from the Microsoft Store. It will not even download nor it will install it!

Also, take a look at the “Store Event log”.  To translate it: “Packet distribution is blocked by a policy”.

Also,, downloading and installing the App Package manually will be restricted, and you will be prompted with an error code: 0x800704ec and the mention that it is blocked by Applocker.

Please note

Not all apps in the Microsoft Store are Store Apps! For example Discord or GIMP. Those apps aren’t UWP apps but Win32Apps

Guess what doesn’t block Win32 Apps from being installed from the Microsoft Store. Yep!! Appx Applocker Rules. To block Win32Apps from being installed, you also need to make sure you deploy an Applocker policy to restrict executables from launching.

Deploy Applocker to Intune with PowerShell (call4cloud.nl)

3. Preventing access to the whole Microsoft App Store

When you don’t want to go down the road to limit access to the store, you could also block access to the Microsoft App Store. But you must ask yourself: Do you really want to block the Microsoft App store?

BEWARE!!!:

When you prevent access to the whole Microsoft Store for your whole device instead of your users, all of your Modern Apps are not going to be updated because they can only be updated via the Store or Windows Updates for Business, not with existing software management solutions or WSUS. Does this sound like a security/vulnerability problem to me? Yes, it does!

Device

HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\WindowsStore\RemoveWindowsStore REG_DWORD 1

User:

HKEY_CURRENT_USER\Software\Policies\Microsoft\WindowsStore\RemoveWindowsStore REG_DWORD 1

If you enable this setting, access to the Store application is denied. As mentioned earlier access to the Store is required for installing app updates.

Still, reading? You could configure this setting by configuring an administrative Template. Beware! This policy is not going to work when you have a Windows 10 Pro license, you will need enterprise!

Testing it!

4. Turning off access to the Microsoft Store??

If preventing access to the Microsoft Store is not enough, we could also remove the possibility to search the whole Microsoft Store. Let’s look at this administrative template: “Turn off access to the store” and what Microsoft has to say about it.

When reading the above text, we will know when we configure this option the end-user will not have the possibility to “open with” anymore when they try to open a file with an unhandled file type. HUH? So, turning off access to the Microsoft Store will only remove the possibility of searching the Microsoft Store when you have a file with an unknown file protocol?

I have created a simple file with a file extension to test it. ubk

As shown above, no Microsoft Store…… but changing it back to .txt will return the possibility to “search the Microsoft Store.”

So please skip this one!… The name Microsoft has given it doesn’t do what you would expect when you are reading the title: Turn off access to the Microsoft Store. But I needed to mention this policy because I think it’s a weird one.

5. Removing all Access to the Microsoft Store and installed Apps

If you want to step it up a notch, you could also remove all access to the Microsoft Store and all installed applications.

Unfortunately, there is no GUI method for configuring this setting. Luckily, a CSP is available. (Beware of the Enterprise requirement!)

OMA-Uri:

./User/Vendor/MSFT/Policy/Config/ApplicationManagement/DisableStoreApps

Data Type : Integer

Value: 1

When the CSP is deployed to your device you could try to open the Microsoft Store. It will give you a nice error message

BEWARE: It also blocks the Company Portal App! Check out this blog to read the whole story behind it!

6. Blocking App Store packages only

Now we have made sure the Microsoft App Store is limited or blocked we also need to take a look at how to prevent manually Appx installations because they don’t need the store to install Apps? Of course, when you have configured Applocker, the Applocker rules will also be applied when you want to install the appx files manually

If you enable this policy, non-administrators will be unable to initiate the installation of Windows app packages.

But beware: All users will still be able to install Windows app packages via the Microsoft Store!!

You can configure this setting by also creating a new settings catalog: Block Non Admin user Install aka BlockNonAdminUserInstall

Okay, it looks kinda weird you need to switch the flip to Allow… but reading the information will show you what to choose!

“If you enable this policy, non-administrators will be unable to initiate the installation of Windows app packages.”

“If you disable or do not configure this policy, all users will be able to initiate the installation of Windows app packages”

TESTING IT

Download yourself an Appx Package and try to install it

https://github.com/microsoft/winget-cli/releases/download/v-0.2.10191-preview/Microsoft.DesktopAppInstaller_8wekyb3d8bbwe.appxbundle

As shown below, we will end up with the error BlockNonAdminUserInstall and the error code 0x80070005

Conclusion:

Why block access to the Microsoft Store, when you can manage it? Blocking access to the Microsoft Store is not the way to go in my opinion!!!!