How do you de-elevate privileges for a child process

Question

I know how to launch a process with Admin privileges from a process using:

proc.StartInfo.UseShellExecute = true;
proc.StartInfo.Verb = "runas";

where proc is a System.Diagnostics.Process. But how does one do the opposite?

If the process you're in is already elevated, how do you launch the new process without admin privileges? More accurately, we need to launch the new process with the same permission level as Windows Explorer, so no change if UAC is disabled, but if UAC is enabled, but our process is running elevated, we need to perform a certain operation un-elevated because we're creating a virtual drive and if it's created with elevated permissions and Windows explorer is running unelevated it won't show up.

Feel free to change the title to something better, I couldn't come up with a good description.

Answer 1

You can use ProcessStartInfo.UserName and ProcessStartInfo.Password to specify the account you want your process to run under.

class Program
{
    static void Main(string[] args)
    {
        var psi = new ProcessStartInfo(@"c:\windows\system32\whoami.exe");
        var password = new SecureString();
        password.AppendChar('s');
        password.AppendChar('e');
        password.AppendChar('c');
        password.AppendChar('r');
        password.AppendChar('e');
        password.AppendChar('t');
        psi.Password = password;
        psi.UserName = "username";
        psi.UseShellExecute = false;
        psi.RedirectStandardOutput = true;

        var p = new Process();
        p.StartInfo = psi;
        p.Start();
        p.WaitForExit();

        Console.WriteLine(p.StandardOutput.ReadToEnd());
    }
}

Answer 2

We ended up using the sample from this Code Project article: High elevation can be bad for your application: How to start a non-elevated process at the end of the installation

It seems to work so far, I gather it injects into RunDll32.exe, my C++/Win32 is fairly weak so I didn't look too much into the actual implementation, just it's use. Confirmed that it works in Vista and Win7 both x86 and x64 (at least for us, x86 and x64 require different dll's which is checked for at install time and the proper one is used).