25, 465, 587 - SMTP

Banner Grabbing

Telnet

telnet 10.0.0.3 25

Netcat

nc -n 10.0.0.3 25

Openssl (SMTPS)

openssl s_client -starttls smtp -crlf -connect 10.0.0.3:587

Parameters

• s_client: SSL/TLS client program.

• -starttls <protocol>: send the protocol-specific message(s) to switch to TLS for communication.

• -crlf: translate a line feed from the terminal into CR+LF.

Enumeration

smtp-commands NSE Script

nmap -p 25,465,587 --script smtp-commands 10.0.0.3

smtp-enum-users NSE Script

nmap -p 25,465,587 --script smtp-enum-users 10.0.0.3

NTLM Information Disclosure

On Windows, with NTLM authentication enabled, sending a SMTP NTLM authentication request with null credentials will cause the remote service to respond with a NTLMSSP message disclosing information to include NetBIOS, DNS, and OS build version.

Manually

telnet example.com 587
...
>> HELO
250 example.com Hello [x.x.x.x]
>>AUTH NTLM 334
NTLM supported
>>TlRMTVNTUAABAAAAB4IIAAAAAAAAAAAAAAAAAAAAAAA=
334 TlRMTVNTUAACAAAACgAKADgAAAAFgooCBqqVKFrKPCMAAAAAAAAAAEgASABCAAAABgOAJQAAAA9JAEkAUwAwADEAAgAKAEkASQBTADAAMQABAAoASQBJAFMAMAAxAAQACgBJAEkAUwAwADEAAwAKAEkASQBTADAAMQAHAAgAHwMI0VPy1QEAAAAA

smtp-ntlm-info NSE Script

nmap -p 587 --script smtp-ntlm-info --script-args smtp-ntlm-info.domain=example.com 10.0.0.3

Commands

HELO        Identify to the SMTP server.
EHLO        Alternative HELO for Extended SMTP protocol.
MAIL FROM:  Sender's email address.
RCPT TO:    Recipient's email address.
DATA        Initiate message content transfer. Command is terminated with a line containing only a .
RSET        Reset the session. Connection will not be closed.
VRFY        Verify username or mailbox.
NOOP        No-op. Keeps connection open.
QUIT        Ends session.

Note: Sessions must start with HELO and end with QUIT.

Configuration files

sendmail.cf
submit.cf

Other

The following Python script opens a TCP socket, connects to the SMTP server, and issues a VRFY command for a given username:

#!/usr/bin/python
import socket
import sys

if len(sys.argv) != 2:
        print "Usage: vrfy.py <username>"
        sys.exit(0)

# Create a Socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Connect to the Server
connect = s.connect(('10.11.1.217',25))

# Receive the banner
banner = s.recv(1024)
print banner

# VRFY a user
s.send('VRFY ' + sys.argv[1] + '\r\n')
result = s.recv(1024)
print result

# Close the socket
s.close()