deepblue/windows-itpro-docs
1
0
Fork 0
mirror of https://github.com/MicrosoftDocs/windows-itpro-docs.git synced 2025-05-28 05:07:23 +00:00
Code Issues Actions 3 Packages Projects Releases Wiki Activity

Update use-windows-defender-application-control-with-dynamic-code-security.md

Browse Source
This commit is contained in:
jsuther1974 2022-08-10 17:45:16 -07:00
parent 1c552710af
commit 250baa6a9f
1 changed files with 3 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
windows/security/threat-protection/windows-defender-application-control/use-windows-defender-application-control-with-dynamic-code-security.md
View File

@ -20,13 +20,13 @@ ms.technology: windows-sec
# Windows Defender Application Control (WDAC) and .NET
.NET apps (as written in a high-level language like C#) are compiled to an Intermediate Language (IL). IL is a compact code format that can be supported on any operating system or architecture. Most .NET apps use APIs that are supported in multiple environments, requiring only the .NET runtime to run. IL needs to be compiled to native code in order to execute on a CPU, for example Arm64 or x64. When .NET compiles IL to native image (NI) on a device with a WDAC user mode policy, it first checks whether the original IL file passes the current WDAC policies. If so, .NET sets a NTFS extended attribute (EA) on the generated NI file so that WDAC knows to trust it as well. When the .NET app runs, WDAC sees the EA on the NI file and allows it.
.NET apps (as written in a high-level language like C#) are compiled to an Intermediate Language (IL). IL is a compact code format that can be supported on any operating system or architecture. Most .NET apps use APIs that are supported in multiple environments, requiring only the .NET runtime to run. IL needs to be compiled to native code in order to execute on a CPU, for example Arm64 or x64. When .NET compiles IL to native image (NI) on a device with a WDAC user mode policy, it first checks whether the original IL file passes the current WDAC policies. If so, .NET sets an NTFS extended attribute (EA) on the generated NI file so that WDAC knows to trust it as well. When the .NET app runs, WDAC sees the EA on the NI file and allows it.
The EA set on the NI file only applies to the currently active WDAC policies. If one of the active WDAC policies is updated or a new policy is applied, the EA on the NI file is invalidated. The next time the app runs, WDAC will block the NI file. .NET handles this gracefully and will fall back to the original IL code. If the IL still passes the latest WDAC policies, then the app runs without any functional impact. Since the IL is now being compiled at runtime, you may notice a slight impact to performance of the app. When this happens, .NET will also schedule a process to run at the next maintenance window to regenerate all NI files, thus reestablishing the WDAC EA for all code that passes the latest WDAC policies.
The EA set on the NI file only applies to the currently active WDAC policies. If one of the active WDAC policies is updated or a new policy is applied, the EA on the NI file is invalidated. The next time the app runs, WDAC will block the NI file. .NET handles the block gracefully and will fall back to the original IL code. If the IL still passes the latest WDAC policies, then the app runs without any functional impact. Since the IL is now being compiled at runtime, you may notice a slight impact to performance of the app. When .NET must fall back to IL, .NET will also schedule a process to run at the next maintenance window to regenerate all NI files, thus reestablishing the WDAC EA for all code that passes the latest WDAC policies.
In some cases, if an NI file is blocked, you may see a "false positive" block event in the *CodeIntegrity - Operational* event log as described in [WDAC Admin Tips & Known Issues](/windows/security/threat-protection/windows-defender-application-control/operations/known-issues.md#net-native-images-may-generate-false-positive-block-events).
To mitigate any performance impact caused when the WDAC EA is not valid or missing, use any of the following strategies:
To mitigate any performance impact caused when the WDAC EA isn't valid or missing, use any of the following strategies:
1. Work with the app developer to pre-compile their NI and digitally sign it. Then, ensure your WDAC policies allow that signature;
2. Run *ngen.exe update* to force .NET to regenerate all NI files immediately after applying changes to your WDAC policies;