Lab: Shellshock netcat

Step: 4

• Netcat is a program that helps developing and testing network programs.
• There are way too many options to discuss here, but we need this tool.
• A bit of background
  • For the most part, every computer on the internet has an IP address.
    • We can see this by typing ifconfig
    • look for an entry like

       inet addr: 10.0.2.15 

    • WRITE THIS DOWN, you will need it multiple times.
    • This will be different on different machines.
    • This number, 10.0.2.15 in this case identifies your machine.
    • This is somewhat of a lie, but live with it for now.
  • In addition, each machine supports a number of network ports.
    • Think of the ip address as a building.
    • And the port as a room number.
  • For the most part, httpd is on port 80
  • https is on port 443
  • Look at /etc/services for a standard list of ports.
  • Ports below 1024 are special and usually locked.
  • We will use port 9090 for our experiments.
• Netcat (nc) can act as either a "client" or a "server"
• Client demo
  • Your machine is running a web server.
  • We can talk to that web server using nc
    • $ represents the prompt.
    • 10.0.2.15 is the ip address of the local server.
    • After the nc command type GET index.html

    • $ nc 10.0.2.15 80
      GET index.html

    • The first argument is the computer, the second is the port
    • You will see a message that states you are not using http:2.0
• Server demo
  • Start a second terminal
    • Run the following command
    • nc -l 9090 -v
    • -l says listen for incoming connections on port 9090
    • -v says to be verbose
  • This starts netcat listening on port 9090 in verbose mode.
  • In a different terminal run a client
    • nc localhost 9090
    • or nc 10.0.2.15 9090
  • Notice you can type in the client window and it will be echoed on the server window.
  • You can also type in the server window and it will be echoed on the client.
• We will use nc in server mode later.