White Hat Security Guide "How To Hack With Telnet"

This is a White Hat computer security training guide. To use this guide you must have your own TCP/IP network. This can be as simple as two computers connected over a single wire connection or as complex as a network with thousands of routers. Casual readers are advised that if you use these procedures on any network, such as the networks connected to the Internet, without the permission of the owner that it could be a violation of national or international law. If you are responsible for the security of one or more Internet networks this guide can significantly enhance your understanding of how exploitation of networks is accomplished using the very simple hacker Telnet protocol.

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Telnet is an Internet Network Virtual Terminal (NVT) protocol that is easier to use than to explain. The Telnet protocol is used by other Internet applications, such as the Control Connection in FTP, so knowledge of Telnet is useful within multiple applications. This general applicability of Telnet within the Internet enables a hacker to reap lots of information and potentially exert control over many applications. By using Telnet, a human hacker can emulate any number of Internet applications disguising the human as just another Internet computer.

Within the Internet, each application (Well Known Port) is assigned a number in accordance with Internet Standard 002. A few of these numbers are enumerated below:

Internet Application Numbers


WWW Example - Use of Telnet to emulate a WWW client for information gathering.

telnet 80  
Telnet to server application port 80
note: the server will not provide an automatic response...
GET / HTTP 1.1  

Instruct the WWW server to return 
data using HTTP 1.1 format

HTTP/1.1 200 OK
Date: Mon, 05 Nov 2007 14:55:33 GMT
Server: Apache/2.2.3 (FreeBSD) DAV/2
PHP/5.1.6 with Suhosin-Patch mod_ssl/2.2.3 OpenSSL/0.9.7e-p1
Last-Modified: Mon, 08 Oct 2007 00:41:47 GMT
ETag: "1c8216-2562-847088c0"
Accept-Ranges: bytes
Content-Length: 9570
Connection: close
! Content-Type: text/html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/
<html xmlns="http://www.w3.org/1999/xhtml">

Lots of information is returned. We see that the 
web server is running on a FreeBSD Unix server. 
The WWW server is Apache version 2.2.3. 
The server is also running PHP version 
5.1.6 and SSL version 0.9.7.

SMTP (email) Spoofing Example - Use of Telnet 
to hack (forge) email

telnet 25  
Telnet to the email application
Connected to host.
Escape character is '^]'.
220 ESMTP Sendmail 8.13.8/8.13.8; Mon, 5 Nov 2007 10:42:59 -0500 (EST)
Server response.
Make up a hostname...or pick a real hostname 
from DNS
The remote server returns  
250 Hello [], 
pleased to meet you
MAIL FROM: <[email protected]>  
Type any address you like
Server accepts address  
250 2.1.0 <This email address is being protected from spambots. You need JavaScript enabled to view it.>
... Sender ok
RCPT TO:<This email address is being protected from spambots. You need JavaScript enabled to view it.>  
This should be a username used within this domain...
Server checks its usernames then replies Recipient ok
Server replies 354 Enter mail, end with "." 
on a line by itself

Type your message followed by a line with just a period.


Server replies 250 2.0.0 lA5FgxM4000833 Message accepted for delivery
Server replies 221 2.0.0 closing connection
Connection closed by foreign host.

Resulting Message...

From This email address is being protected from spambots. You need JavaScript enabled to view it. Tue Nov 6 12:04:30 2007
Date: Tue, 6 Nov 2007 12:01:19 -0500 (EST)
From: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: Email Forgery
To: undisclosed-recipients:;

This email was forged using the Telnet protocol.


Telnet is a simple protocol designed to provide compatible terminal services across TCP/IP networks. The simple character mode design of the Internet Protocols like Telnet make them great tools for hackers looking for information about your hardware and software infrastructure. Telnet provides you with an excellent White Hat tool to familiarize yourself with this level of network interactions. The knowledge will prove itself invaluable as you configure routers, switches, and other devices on your network.

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