Why does my IL generated Assembly, ilasm.exe called by C#, need UAC?

Question

I'm trying to compile an IL Code to an Assembly. The ilasm.exe should get called by my C# Application. I'm invoking the ilasm.exe through an ProcessStartInfo Instance. The generation of the PE works fine and my Assembly is working.

My problem is that the files that were created by my application, afterwards need administrator privileges to be executed.

If I call ilasm.exe manually from command line, no admin rights are needed.

Used ilasm.exe command: ilasm.exe /qui /output="c:\test\newFile.exe" <path to il file>

My Application calling the ilasm.exe:

ProcessStartInfo startInfo = new ProcessStartInfo();
startInfo.CreateNoWindow = false;
startInfo.UseShellExecute = false;
startInfo.FileName = @"C:\Windows\Microsoft.NET\Framework\v4.0.30319\ilasm.exe";
startInfo.WindowStyle = ProcessWindowStyle.Hidden;
startInfo.Arguments = ilFilePath + " /qui /output=" + outputPath + "testFile.exe";


try
{
    using (Process exeProcess = Process.Start(startInfo))
    {
        exeProcess.WaitForExit();
    }
}
catch
{
    // Log error.
}

Am I doing anything wrong? Do I need to specify anything else when calling another Process from C#?

I'm running my Application and the commandline without admin rights.

Answer 1

It's requiring UAC because you're not supplying a path to a writable location in output, so it's trying to write to the same folder ilasm is in (or the current folder for your app).

A non-admin user doesn't have write access to anything under %WINDIR% (the Windows folder) or %ProgramFiles%, so it's asking for elevation to a user that does have write access to the folder.

Answer 2

What is patchFile?

This comment by @Chris is relevant to this puzzle, I don't see it in the question. You are probably dealing with a difficult problem that Microsoft needed to solve with UAC. Supporting old programs that need UAC privileges but don't ask for it because they were written before Vista. Like installers. And patch programs.

My crystal ball says that your actual program name is not newFile.exe like your question says but has a name like "update.exe" or "patch.exe". And furthermore, it isn't obvious either, that you don't include a manifest in the program you generated. A manifest that says that the program is Vista aware with the <requestedExecutionLevel> element. And furthermore, also not obvious, that when you run this from the command line by hand that you use another name for the .exe.

That's a lot of guesses, but put them together and it makes sense: Windows goes "aha! Old program, sounds like it is going to want to write to .exe files in a restricted directory. Better display the UAC prompt".