C#: Creating and Sending UDP Packets


I needed to test an application today that accepts UDP packets so I searched the internet for a simple program to create and send UDP packets and found a bunch of complex programs that didn’t work (or at least that I couldn’t figure out within a couple of minutes!). So, after I wasted a bunch of time I just decided to write my own method to create and send the UDP packets myself. I would have saved a ton of time had I just done this from the beginning!

using System.Net;
using System.Net.Sockets;

...

/// <summary>
/// Sends a sepcified number of UDP packets to a host or IP Address.
/// </summary>
/// <param name="hostNameOrAddress">The host name or an IP Address to which the UDP packets will be sent.</param>
/// <param name="destinationPort">The destination port to which the UDP packets will be sent.</param>
/// <param name="data">The data to send in the UDP packet.</param>
/// <param name="count">The number of UDP packets to send.</param>
public static void SendUDPPacket(string hostNameOrAddress, int destinationPort, string data, int count)
{
    // Validate the destination port number
    if (destinationPort < 1 || destinationPort > 65535)
        throw new ArgumentOutOfRangeException("destinationPort", "Parameter destinationPort must be between 1 and 65,535.");

    // Resolve the host name to an IP Address
    IPAddress[] ipAddresses = Dns.GetHostAddresses(hostNameOrAddress);
    if (ipAddresses.Length == 0)
        throw new ArgumentException("Host name or address could not be resolved.", "hostNameOrAddress");

    // Use the first IP Address in the list
    IPAddress destination = ipAddresses[0];            
    IPEndPoint endPoint = new IPEndPoint(destination, destinationPort);
    byte[] buffer = Encoding.ASCII.GetBytes(data);

    // Send the packets
    Socket socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);           
    for(int i = 0; i < count; i++)
        socket.SendTo(buffer, endPoint);
    socket.Close();            
}

Update: So, it turns out that the .NET Framework actually already has a class for sending UDP packets called UdpClient. The documentation for it can be found here. It definitely provides a lot more options but if you are looking for a simple method, the above works too!

Reverse DNS Lookup Using cmd.exe


Here is an awesome script that utilizes cmd.exe for reverse DNS lookup. It was posted on the Security Reliks blog by Skyler Onken.

WEAPONIZING CMD.EXE – DNS REVERSE LOOKUP

Enjoy!

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