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title, description, ms.manager, ms.date, ms.topic, ms.localizationpriority
| title | description | ms.manager | ms.date | ms.topic | ms.localizationpriority |
|---|---|---|---|---|---|
| WDAC Admin Tips & Known Issues | WDAC Known Issues | jsuther | 11/22/2023 | article | medium |
WDAC Admin Tips & Known Issues
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 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.
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Explicit deny rules - a file is blocked if any explicit deny rule exists for it, 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.
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Explicit allow rules - if any explicit allow rule exists for the file, the file runs.
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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.
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Lastly, WDAC makes a cloud call to the ISG to get reputation about the file, if the policy enables the ISG option.
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If no explicit 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 will 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.
Audit mode policies can change the behavior for some apps or cause app crashes
Although WDAC audit mode is designed to avoid impact to apps, some features are always on/always enforced with any WDAC policy that includes the option 0 Enabled:UMCI. Here's a list of known system changes in audit mode:
- Some script hosts might block code or run code with fewer privileges even in audit mode. See Script enforcement with WDAC for information about individual script host behaviors.
- Option 19 Enabled:Dynamic Code Security is always enforced if any UMCI policy includes that option. See WDAC and .NET.
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 were 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 regenerates the native image at its next scheduled maintenance window.
Signatures using elliptical curve cryptography (ECC) aren't supported
WDAC signer-based rules only work with RSA cryptography. ECC algorithms, such as ECDSA, aren't supported. If you try to allow files by signature based on ECC signatures, you'll see VerificationError = 23 on the corresponding 3089 signature information events. You can authorize the files instead by hash or file attribute rules, or using other signer rules if the file is also signed with signatures using RSA.
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
Slow boot and performance with custom policies
WDAC evaluates all processes that run, including inbox Windows processes. If policies don't build off the WDAC templates or don't trust the Windows signers, you'll see slower boot times, degraded performance and possibly boot issues. For these reasons, you should use the WDAC base templates whenever possible to create your policies.
AppId Tagging policy considerations
If the AppId Tagging Policy wasn't built off the WDAC base templates or doesn't allow the Windows in-box signers, you'll notice a significant increase in boot times (~2 minutes).
If you can't allowlist the Windows signers, or build off the WDAC base templates, it's recommended to add the following rule to your policies to improve the performance:
:::image type="content" source="../images/known-issue-appid-dll-rule.png" alt-text="Allow all dlls in the policy.":::
:::image type="content" source="../images/known-issue-appid-dll-rule-xml.png" alt-text="Allow all dll files in the xml policy.":::
Since AppId Tagging policies evaluate but can't tag dll files, this rule will short circuit dll evaluation and improve evaluation performance.