Network Security Tools

Overview of SMTP Authentication

In this section we will demonstrate how to add SMTP authentication protocol support to Hydra. Mail servers commonly use SMTP authentication to identify a user as being valid prior to accepting email for delivery.

A number of different standards for SMTP authentication exist, many of which are not RFC standards. We are demonstrating an authentication method using the AUTH LOGIN method, as shown in Example 3-1.

Example 3-1. An SMTP AUTH session

220-mail.xxxxxxxx.com ESMTP Exim 4.34 #1 Wed, 23 Jun 2004 17:35:13 -0700 
EHLO mail.myserver.com
250-mail.xxxxxxxx.com Hello mail.myserver.com [192.168.0.156]
250-SIZE 52428800
250-PIPELINING
250-AUTH PLAIN LOGIN
250-STARTTLS
250 HELP
AUTH LOGIN
334 VXNlcm5hbWU6
bXl1c2VybmFtZQ==
334 UGFzc3dvcmQ6
bXlwYXNzd29yZA==
235 Authentication succeeded

The AUTH LOGIN authentication method is well supported by many common SMTP servers, and as such, it is a good protocol to use. The protocol is a simple process that uses unencrypted credentials. Even though the protocol is insecure, a number of mail servers support it in their default configurations as a lowest-common-denominator protocol for SMTP authentication.

The protocol can be demonstrated by using the telnet command to port 25 on an available mail server. The mail server then responds with a connection message:

220-mail.xxxxxxxx.com ESMTP Exim 4.34 #1 Wed, 23 Jun 2004 17:35:13 -0700

The mail server responds with a header containing the SMTP response code 220. Similar to ...