File Transfer Protocol (FTP) is, as the name suggests , a protocol used to allow remote transfer of files over a network. It uses a client-server model to do this, and- as we'll come on to later- relays commands and data in a very efficient way.
A typical FTP session operates using two channels:
As their names imply, the command channel is used for transmitting commands as well as replies to those commands, while the data channel is used for transferring data.
FTP operates using a client-server protocol. The client initiates a connection with the server, the server validates whatever login credentials are provided and then opens the session.
While the session is open, the client may execute FTP commands on the server.
The FTP server may support either Active or Passive connections, or both.
This separation of command information and data into separate channels is a way of being able to send commands to the server without having to wait for the current data transfer to finish. If both channels were interlinked, you could only enter commands in between data transfers, which wouldn't be efficient for either large file transfers, or slow internet connections.
Try to connect to iy anonymously using the username and passwrod as anonymous and see if you can find something or some files that you can access this should always be your first step if you see the port 21 open.
Similarly to Telnet, when using FTP both the command and data channels are unencrypted. Any data sent over these channels can be intercepted and read.
With data from FTP being sent in plaintext, if a man-in-the-middle attack took place an attacker could reveal anything sent through this protocol (such as passwords). An article written by JSCape demonstrates and explains this process using APR-Poisoning to trick a victim into sending sensitive information to an attacker, rather than a legitimate source.
When looking at an FTP server from the position we find ourselves in for this machine, an avenue we can exploit is weak or default password configurations.