110,995 - Pentesting POP

Basic Information

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

Enumeration

Banner Grabbing

nc -nv <IP> 110
openssl s_client -connect <IP>:995 -crlf -quiet

Manual

You can use the command CAPA to obtain the capabilities of the POP3 server.

Automated

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).

POP3 bruteforce

POP syntax

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: [e-mail]
 Dear Billy Dean,

 Here is your login for remote desktop ... try not to forget it this time!
 username: billydean
 password: PA$$W0RD!Z