Forget AppLocker and all its weaknesses and start using Microsoft Defender Application Control for superior application whitelisting in Windows 10 1903 and later.

This is a guide to get you started within an hour or two with what I call “AppLocker Deluxe” and that is Microsoft Defender Application Control, formerly known as Device Guard and up until recently Windows Defender Application Control (WDAC).

Most customers that did not use AppLocker before Wannacry and other types of ransomware attacks are now using AppLocker to prevent malicious software to run on their Windows devices. As many security specialists have shown, there are numerous ways to bypass AppLocker and still get code to execute. One of them being using regsvr32 to download and execute script directly from the internet for instance.

What is superior to AppLocker is Microsoft Defender Application Guard (MDAC). This takes application whitelisting to a new level and with Windows 10 version 1903 it becomes the first time since Windows 10 launched that it is actually usuable in many common day scenarios as the administration can now be on a level which is really to manage. The reason for this it being rather easy to manage now is primarily:

  • Multiple policies. You can have multiple policies complementing each other so that you do not have to sign everything nor have to create an entirely new baseline each time you want to allow new things to run.
  • Path rules. You can use path rules as of Windows 10 version 1903. As always, this is a balance between security and useability and administration so bear in mind and use this with caution. What is good is that MDAC comes with a use writable protection.

Pre-reqs for getting started

So to get started in something that looks like a real world scebario you need this:

  • 2 physical machines, different hardware models, that run Windows 10 version 1903 or preferably 1909 or later as that gives you some better insights.
  • A couple of hours of your time to get going!

High level steps

  1. Create a baseline on each hardware model.
  2. Merge the baselines into one general baseline.
  3. Create a supplemental policy.
  4. Deploy the two policies.
  5. Start the testing.
  6. Switch from Audit to Enforced mode!

1. Create a baseline on each hardware model

Let’s start with creating a baseline policy from two different machines, which will later be merged to one baseline policy. We will start with auditing, and eventually in the end of this guide switch to enforced mode.

$CIPolicyfileXML = "C:\temp\CIpolicy_model.xml"
New-CIPolicy -MultiplePolicy -filePath $CIPolicyfileXML -ScanPath C: -level FilePublisher -UserPEs -Fallback Hash

Now we set the necessary options for the code integrity policy, which is to use Microsofts Intelligent Security Graph for whitelisting (option 14), to allow supplemental policies to be used (option 17) and then we set Hardware Virtualized Code Integrity (HVCI) to Enabled.

#Automatically trust what Microsoft has deemed trustworthy using the Intelligent Security Graph
Set-RuleOption -FilePath $CIPolicyfileXML -Option 14
#Set the following option to make sure the policy can be applied without reboot
Set-RuleOption -FilePath $CIPolicyfileXML -Option 16
#Set this policy to allow supplemental policies, otherwise we can't supplement this basepolicy
Set-RuleOption -FilePath $CIPolicyfileXML -Option 17
#Now activating Hardware Virtualized Code Integrity (HVCI) and set it to enabled
Set-HVCIOptions -Enabled -FilePath $CIPolicyfileXML

Repeat the above process for at least two models, but preferably for each model you have in your environment (or at least the top five mot used models).

Note: Enabling the Intelligent Security Graph option will white list the installer for 7-Zip for instance. It will then also white list all executables that the 7-Zip installer puts on your system.

2. Merge the baselines into one general baseline

We will now merge the baselines from the two models (or more) and create one single baseline policy.

#When done collecting CIPolicies, merge them to create a common baseline
$CIPolicyfileXMLMerged = "C:\temp\Merged.xml"
$CIPolicyfileBin = "c:\temp\Merged.cip"
Merge-CIPolicy -OutputFilePath C:\temp\merged.xml -PolicyPaths "C:\temp\CIPolicy_modelX.xml","C:\temp\CIPolicy_modellY.xml"
#Then convert to binary format
ConvertFrom-CIPolicy -XmlfilePath $CIPolicyfileXMLMerged -BinaryFilePath $CIPolicyfileBin

Last but not least you must change the name of the Merged.cip file to match the Policy ID of the file which can be found at the bottom in the Merged.xml file, see the <PolicyID> section. The end result should look like {76300157-42A0-4A2D-A383-AF140D64AAE0}.cip.

3. Create a supplemental policy

Now we will create the first supplemental policy to supplement the baseline policy created in step 1 and 2. This is using path rules which is something that was added with Windows 10 version 1903.

#Now create a supplemental policy with file path rules
$CIPolicyfileXMLSupplemental = "C:\temp\Supplemental.xml"
$rules = New-CIPolicyRule -FilePathRule "C:\Program files\*"
$rules += New-CIPolicyRule -FilePathRule "C:\Program files (x86)\*"
$rules += New-CIPolicyRule -FilePathRule "\\server1\installation\*"
New-CIPolicy -FilePath $CIPolicyfileXMLSupplemental -Rules $rules -UserPEs
Set-CIPolicyIdInfo -FilePath $CIPolicyfileXMLSupplemental -BasePolicyToSupplementPath $CIPolicyfileXMLMerged
#now lookup the PolicyGUID from the bottom of the Supplemental.xml file.
ConvertFrom-CIPolicy -XmlFilePath $CIPolicyfileXMLSupplemental -Binary Supplemental.cip

You must change the name of the Supplemental.cip file to match the Policy ID of the supplemental file which can be found at the bottom in the Supplemental.xml file, see the <PolicyID> section. The end result should look like {56B75B7A-06D3-49EF-BCF8-8FC47C6ADA20}.cip.

4. Deploy the two policies

Now, lets deploy the two policies by copying them to C:\Windows\System32\CodeIntegrity\CIPolicies\Active.

For the sake of it, restart the machine. You could also use the below PowerShell command to refresh the policy without reboot:

Invoke-CimMethod -Namespace root\Microsoft\Windows\CI -ClassName PS_UpdateAndCompareCIPolicy -MethodName Update -Arguments @{FilePath = 'C:\Windows\System32\CodeIntegrity\CiPolicies\Active\{GUID}.cip'}

5. Start the testing

Now you can start the testing and see what is blocked by fetching the log files which are located in Event Viewer under Applications and Services Logs > Microsoft > Windows > Code Integrity > Operational.

6. Switch from audit mode to enforced mode!

Out of everything that would have been blocked by fetching the logs as mentioned in step 5, create additional supplemental policies and deploy until everything you need to run is white listed. Then, switch from audit mode to enforced!

Set-RuleOption -FilePath $CIPolicyfileXML -Delete -Option 3

Deploying via Intune

Even though there are existing configuration settings for enabling Microsoft Defender Application Control in an Intune endpoint restrictions policy, enabling it via those settings will mean very limited control and you cannot use supplemental policies. So, therefore you need to deploy these control policies in another way.

1. Create a source folder in C:\ named MDAC, in which you create a folder named Source, where you copy the .CIP files.

2. Create a textfile named SchTask.ps1 and add the following content.

New-Item -Path "c:\" -Name "CI" -ItemType "directory"
Copy-Item -Path ".\{76300157-42A0-4A2D-A383-AF140D64AAE0}.cip" -Destination "C:\CI" -Force
Copy-Item -Path ".\{56B75B7A-06D3-49EF-BCF8-8FC47C6ADA20}.cip" -Destination "C:\CI" -Force
Copy-Item -Path ".\MDAC.ps1" -Destination "C:\CI" -Force
$Time = New-ScheduledTaskTrigger -Once -At 12:00
$User = "SYSTEM"
$Action = New-ScheduledTaskAction -Execute "powershell.exe" -Argument "-ex bypass -file `"C:\CI\MDAC.ps1`""
Register-ScheduledTask -TaskName "CI" -Trigger $Time -User $User -Action $Action -Force
Start-ScheduledTask -TaskName "CI"
Return 0

3. Create a textfile named MDAC.ps1 and add the following content. 

Copy-Item -Path "C:\CI\{56B75B7A-06D3-49EF-BCF8-8FC47C6ADA20}.cip" -Destination "C:\Windows\System32\CodeIntegrity\CiPolicies\Active" -Force
Copy-Item -Path "c:\CI\{76300157-42A0-4A2D-A383-AF140D64AAE0}.cip" -Destination "C:\Windows\System32\CodeIntegrity\CiPolicies\Active" -Force
Return 0

4. As we will deploy this using a Win32 app, download the Intune content prep tool and run the following command from the extracted IntuneWinAppUtil.exe.

IntuneWinAppUtil.exe -c C:\MDAC\Source -s SchTask.ps1 -o C:\MDAC

5. Create a new Win32 app in Intune and use the following parameters when adding it:

Program install and uninstall command:
powershell.exe -ExecutionPolicy Bypass .\SchTask.ps1
Running as System.

Detection rules:
Type: File
Path: C:\Windows\System32\CodeIntegrity\CiPolicies\Active
File or folder: {GUID}.cip
Detection method: file or folder exists

6. Assign the app and wait for the MDAC policy to apply. This can be verified by running msinfo32.exe and watching the status for Windows Defender Application Control.

Next steps: Looking at the CSP for Application Control for even smoother deploying via Intune.