File Transfer Protocol (FTP). 
Purpose: Facilitates the transfer of files between a client and a server over a network.
Vulnerabilities: Weak authentication (e.g., default credentials), FTP bounce attacks, Command injection, Data leakage, FTP protocol vulnerabilities (e.g., PORT command exploitation), FTP bounce attacks, Brute force attacks.
Tools: Nmap, Hydra, Metasploit, Wireshark, ftp, FileZilla.