DLL Sideloading Attack possible with Non privileged user for .net 7 WinUI3 Windows single exe file (self-contained)

Question

The .net 7 WinUI3 Windows application single executable file (exe) is prone to DLL Side loading attacks to non privileged users(nomraml users).

I published a .net 7 Windows application as single exe file, self-contained.

When I ran this exe, MSASN1.dll is loaded first before the entry of the app even if I did not use DLLImport anywhere in the code, so I couldn't prevent to load it by adding "SetDefaultDllDirectories" at the OnLaunched of app.xaml.cs.

Is this a design of .net self-contained app?

Or is there any method to prevent loading MSASN1.dll by implementing c# codes?

Please refer to the screenshot of Process Monitor.exe.

Thanks.

BR,

Answer 1

Hi @Byoungtaek Min ,

Since MSASN1.dll is likely loaded by the .NET runtime or a system-level component, it is difficult to prevent its loading through application code alone. The SetDefaultDllDirectories function you’ve tried to use is intended to control the directories searched for DLLs, but it doesn’t prevent DLLs from being loaded if they are required by the runtime or the operating system.

If your concern is about DLL side-loading attacks, ensure that your application is running in a secure environment where untrusted DLLs cannot be placed in directories that are searched by the system. You can also consider using features like Windows Defender Application Control (WDAC) to enforce rules about which DLLs can be loaded by your application.

Best Regards.

Jiachen Li

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