Sunday, August 9, 2009

Telnet - Part 1

Although the networking technologies have immensely evolved over the years, some things have remained the same. Telnet is one of them. The use of Telnet is pivotal in understanding the functioning of any network and helps us to develop an exploit. It can also point out the vulnerabilities of a particular network. So let's start with getting to know what exactly is telnet.

Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive communications facility. Telnet can be used to connect to a remote machine through any open port. So virtually, it stands like this. Telnet can intrude any machine with an open port. This is what mesmerizes the black hat hackers about Telnet. The most common use of Telnet stands to enable remote authentication and access.

Some of the common Telnet ports are these:

Port 21 - File Transfer Protocol
Port 22 - SSH Remote Login Protocol
Port 23 - Telnet Server
Port 25 - Simple Mail Transfer Protocol (SMTP)
Port 53 - Domain Name Server (DNS)
Port 69 - Trivial File Transfer Protocol (TFTP)
Port 70 - Gopher
Port 80 - Hyper Text Transfer Protocol (HTTP)

Once you get connected to a remote machine, you need to issue some simple Unix based commands which help you in interacting with the remote service. This can be used to check which services are running on a particular machine. This process is known as daemon tracking.

Black hat hackers can also use telnet to sniff network packets which might contain sensitive information such as usernames and passwords. This is achieved by using telnet and network utilities such as tcpdump and wireshark.

Now let's start by learning how to connect to some remote machine using telnet.

1>>Go to Run and type "cmd"
2>>In the command line type "telnet www.google.com 80".

You just got connected to Google server on port 80.

Note: The web address or URL can be replaced by any valid IP address.
Now try this. Get the IP address of some friend and use a port scanner to search for open ports on their system. Telnet the ports and play around!

Telnet till next time! :D

Related Posts

Telnet Tutorial - Part 2

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