Mail servers often store very sensitive information. It is critical that organizations use strong password policies, so penetration testers need to perform brute force password auditing against them to check for weak passwords.
This recipe will show you how to launch dictionary attacks against SMTP servers with Nmap.
To launch a dictionary attack against an SMTP server with Nmap, enter the following command:
$ nmap -p25 --script smtp-brute <target>If any valid credentials are found, they will be included in the script output section:
PORT STATE SERVICE REASON 25/tcp open stmp syn-ack | smtp-brute: | Accounts | acc0:test - Valid credentials | acc1:test - Valid credentials | acc3:password - Valid credentials | acc4:12345 - Valid credentials | Statistics |_ Performed 3190 guesses in 81 seconds, average tps: 39