Post Office Protocol (POP) is a type of computer networking and Internet standard protocol that extracts and retrieves email from a remote mail server for access by the host machine. POP is an application layer protocol in the OSI model that provides end users the ability to fetch and receive email (from here).
The POP clients generally connect, retrieve all messages, store them on the client system, and delete them from the server. There are 3 versions of POP, but POP3 is the most used one.
Default ports: 110, 995(ssl)
PORT STATE SERVICE
110/tcp open pop3
nc -nv <IP> 110
openssl s_client -connect <IP>:995 -crlf -quiet
You can use the command CAPA to obtain the capabilities of the POP3 server.
nmap --scripts "pop3-capabilities or pop3-ntlm-info" -sV -port <PORT> <IP> #All are default scripts
The pop3-ntlm-info plugin will return some “sensitive” data (Windows versions).
POP commands:
USER uid Log in as "uid"
PASS password Substitue "password" for your actual password
STAT List number of messages, total mailbox size
LIST List messages and sizes
RETR n Show message n
DELE n Mark message n for deletion
RSET Undo any changes
QUIT Logout (expunges messages if no RSET)
TOP msg n Show first n lines of message number msg
CAPA Get capabilities
From here
Example:
root@kali:~# telnet $ip 110
+OK beta POP3 server (JAMES POP3 Server 2.3.2) ready
USER billydean
+OK
PASS password
+OK Welcome billydean
list
+OK 2 1807
1 786
2 1021
retr 1
+OK Message follows
From: [email protected]
Dear Billy Dean,
Here is your login for remote desktop ... try not to forget it this time!
username: billydean
password: PA$$W0RD!Z