The App class is the server. To start the server on port 4444, the command is $java App 4444 To start the client and correspondingly cause google chrome to on the server, the command is $java client 4444 google-chrome The first arg for the port number which server is listening on, second argument for the command attacker intend to execute No hostname required as it is a local loopback. Gadget chain class one magic method -> class two troll method -> class three invoke method