Starting MSTSC using powershell from C#

Question

I am attempting to start an MSTSC / RDP session from C#. For various reasons I've settled on invoking Powershell to do this, partly because I know the powershell commands work, although I wouldn't be averse to attempting other methods to start the session. I have RDSH enabled and am happily able to start multiple RDP sessions on this machine.

Running the following command in Powershell starts the RDP session exactly as I would expect: cmdkey /generic:TERMSRV/localhost /user:username /pass:password; mstsc /v:localhost

Attempting to translate this to C# using the code below and System.Management.Automation.dll however fails with the error:

Invalid connection file (True) specified

Please note that this is a Remote Desktop Connection error, not a powershell or C# error.

The code I am using is:

void StartRDP(string username, string password)
{
    using (PowerShell PowerShellInstance = PowerShell.Create())
    {
        // create cached credential to use for remote session
        PowerShellInstance.AddCommand("cmdkey");
        PowerShellInstance.AddParameter("/generic:TERMSRV/localhost");
        PowerShellInstance.AddParameter("/user:" + username);
        PowerShellInstance.AddParameter("/pass:" + password);

        // append mstsc command
        PowerShellInstance.AddStatement();

        // start remote desktop connection to localhost
        PowerShellInstance.AddCommand("mstsc");
        PowerShellInstance.AddParameter("/v:localhost");

        // invoke command, creating credential and starting mstsc
        PowerShellInstance.Invoke();
    }
}

This is called using:

StartRDP(username, password);

I have also tested it with hardcoded variables with the same result. Any advice much appreciated!

Edit: Having inspected the credentials cached on the system, I can see that this method is appending "True" to the end of all the parameters... see the difference between a credential created directly in Powershell and one created in C#:

Powershell:

Target: LegacyGeneric:target=TERMSRV/localhost
Type: Generic
User: username

C#:

Target: LegacyGeneric:target=TERMSRV/localhost True
Type: Generic
User: username True

This seems to be the issue, although I am no closer to solving it.

What if you add the `mstsc` command as simply more parameters for cmdkey? `PowerShellInstance.AddParameter("; mstsc /v:localhost")` — Theo, Aug 14 '18 at 14:47
@Theo Thanks, but doing so results in no activity at all: I assume because mstsc is not invoked anymore by System.Management.Automation. — Phueal, Aug 14 '18 at 14:59

score 0 · Answer 1 · answered Aug 14 '18 at 15:22

Having further explored this I've identified the issue; leaving this answer here as well in case it helps others in future.

Parameters with an object as well as the parameter (e.g. /username user as opposed to just /username) need to be provided in this format PowerShell.AddParameter("user:","username")

This amended code works:

void StartRDP(string username, string password)
{
    using (PowerShell PowerShellInstance = PowerShell.Create())
    {
        // create cached credential to use for remote session
        PowerShellInstance.AddCommand("cmdkey");
        PowerShellInstance.AddParameter("generic","TERMSRV/localhost");
        PowerShellInstance.AddParameter("user:",username);
        PowerShellInstance.AddParameter("pass:",password);

        // append mstsc command
        PowerShellInstance.AddStatement();

        // start remote desktop connection to localhost
        PowerShellInstance.AddCommand("mstsc");
        PowerShellInstance.AddParameter("/v","localhost");

        // invoke command, creating credential and starting mstsc
        PowerShellInstance.Invoke();
    }   
}

Starting MSTSC using powershell from C#

1 Answers1