C# – Starting a process with credentials from a Windows Service

cnetwindows-services

I have a Windows service that runs as mydomain\userA. I want to be able to run arbitrary .exes from the service. Normally, I use Process.Start() and it works fine, but in some cases I want to run the executable as a different user (mydomain\userB).

If I change the ProcessStartInfo I use to start the process to include credentials, I start getting errors – either an error dialog box that says "The application failed to initialize properly (0xc0000142). Click on OK to terminate the application.", or an "Access is denied" Win32Exception. If I run the process-starting code from the command-line instead of running it in the service, the process starts using the correct credentials (I've verified this by setting the ProcessStartInfo to run whoami.exe and capturing the command-line output).

I've also tried impersonation using WindowsIdentity.Impersonate(), but this hasn't worked – as I understand it, impersonation only affects the current thread, and starting a new process inherits the process' security descriptor, not the current thread.

I'm running this in an isolated test domain, so both userA and userB are domain admins, and both have the Log On as a Service right domain-wide.

Best Answer

When you launch a new process using ProcessStartInfo the process is started in the same window station and desktop as the launching process. If you are using different credentials then the user will, in general, not have sufficient rights to run in that desktop. The failure to initialize errors are caused when user32.dll attempts to initialize in the new process and can't.

To get around this you must first retrieve the security descriptors associated with the window station and desktop and add the appropriate permissions to the DACL for your user, then launch your process under the new credentials.

EDIT: A detailed description on how to do this and sample code was a little long for here so I put together an article with code.

        //The following security adjustments are necessary to give the new 
        //process sufficient permission to run in the service's window station
        //and desktop. This uses classes from the AsproLock library also from 
        //Asprosys.
        IntPtr hWinSta = GetProcessWindowStation();
        WindowStationSecurity ws = new WindowStationSecurity(hWinSta,
          System.Security.AccessControl.AccessControlSections.Access);
        ws.AddAccessRule(new WindowStationAccessRule("LaunchProcessUser",
            WindowStationRights.AllAccess, System.Security.AccessControl.AccessControlType.Allow));
        ws.AcceptChanges();

        IntPtr hDesk = GetThreadDesktop(GetCurrentThreadId());
        DesktopSecurity ds = new DesktopSecurity(hDesk,
            System.Security.AccessControl.AccessControlSections.Access);
        ds.AddAccessRule(new DesktopAccessRule("LaunchProcessUser",
            DesktopRights.AllAccess, System.Security.AccessControl.AccessControlType.Allow));
        ds.AcceptChanges();

        EventLog.WriteEntry("Launching application.", EventLogEntryType.Information);

        using (Process process = Process.Start(psi))
        {
        }
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