windows-itpro-docs/windows/security/threat-protection/windows-defender-application-control/operations/known-issues.md

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WDAC Admin Tips & Known Issues	WDAC Known Issues	security, malware	windows-client	ITPro	jsuther1974	jogeurte	jogeurte	jsuther	aaroncz	04/04/2023	itpro-security	article	medium

WDAC Admin Tips & Known Issues

Applies to:

• Windows 10
• Windows 11
• Windows Server 2016 and later

Note

Some capabilities of Windows Defender Application Control are only available on specific Windows versions. Learn more about the Application Control feature availability.

This article covers tips and tricks for admins and known issues with Windows Defender Application Control (WDAC). Test this configuration in your lab before enabling it in production.

WDAC policy file locations

Multiple policy format WDAC policies are found in the following locations depending on whether the policy is signed or not, and the method of policy deployment that was used.

• <OS Volume>\Windows\System32\CodeIntegrity\CiPolicies\Active\{PolicyId GUID}.cip
• <EFI System Partition>\Microsoft\Boot\CiPolicies\Active\{PolicyId GUID}.cip

The {PolicyId GUID} value is unique by policy and defined in the policy XML with the <PolicyId> element.

For single policy format WDAC policies, in addition to the two preceding locations, also look for a file called SiPolicy.p7b that may be found in the following locations:

• <EFI System Partition>\Microsoft\Boot\SiPolicy.p7b
• <OS Volume>\Windows\System32\CodeIntegrity\SiPolicy.p7b

Note

A multiple policy format WDAC policy using the single policy format GUID {A244370E-44C9-4C06-B551-F6016E563076} may exist under any of the policy file locations.

File Rule Precedence Order

When the WDAC engine evaluates files against the active set of policies on the device, rules are applied in the following order. Once a file encounters a match, WDAC stops further processing.

1. Explicit deny rules - if any explicit deny rule exists for the file, it's blocked even if other rules are created to try to allow it. Deny rules can use any rule level. Use the most specific rule level practical when creating deny rules to avoid blocking more than you intend.

2. Explicit allow rules - if any explicit allow rul exists for the file, it's allowed by the policy.

3. WDAC then checks for the Managed Installer extended attribute (EA) or the Intelligent Security Graph (ISG) EA on the file. If either EA exists and the policy enables the corresponding option, then the file is allowed.

4. Lastly, WDAC makes a cloud call to the ISG to get reputation about the file, if the policy enables the ISG option.

5. If no rule exists for the file and it's not allowed based on ISG or MI, then the file is blocked implicitly.

Known issues

Boot stop failure (blue screen) occurs if more than 32 policies are active

If the maximum number of policies is exceeded, the device may bluescreen referencing ci.dll with a bug check value of 0x0000003b. Consider this maximum policy count limit when planning your WDAC policies. Any Windows inbox policies that are active on the device also count towards this limit.

Managed Installer and ISG may cause excessive events

When Managed Installer and ISG are enabled, 3091 and 3092 events are logged when a file didn't have Managed Installer or ISG authorization, regardless of whether the file was allowed. These events have been moved to the verbose channel beginning with the September 2022 Update Preview since the events don't indicate an issue with the policy.

.NET native images may generate false positive block events

In some cases, the code integrity logs where Windows Defender Application Control errors and warnings are written include error events for native images generated for .NET assemblies. Typically, native image blocks are functionally benign as a blocked native image falls back to its corresponding assembly and .NET will regenerate the native image at its next scheduled maintenance window.

MSI installers are treated as user writeable on Windows 10 when allowed by FilePath rule

MSI installer files are always detected as user writeable on Windows 10, and on Windows Server 2022 and earlier. If you need to allow MSI files using FilePath rules, you must set option 18 Disabled:Runtime FilePath Rule Protection in your WDAC policy.

MSI Installations launched directly from the internet are blocked by WDAC

Installing .msi files directly from the internet to a computer protected by WDAC fails. For example, this command fails:

msiexec –i https://download.microsoft.com/download/2/E/3/2E3A1E42-8F50-4396-9E7E-76209EA4F429/Windows10_Version_1511_ADMX.msi

As a workaround, download the MSI file and run it locally:

msiexec –i c:\temp\Windows10_Version_1511_ADMX.msi