Everhart, Glenn
From:	Neil Moore-Smith [nms@crescendo.ltd.uk]
Sent:	Tuesday, August 11, 1998 6:41 PM
To:	'rick petersen'; 'ntsecurity@iss.net'
Subject:	RE: [NTSEC] Telnet to ports

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Contact ntsecurity-owner@iss.net for help with any problems!
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Rick

A port is like a telephone extension. The IP address is the number of the 
company you need to contact, the "extension" gets you through to the person 
you want to speak to, or in this case, the service, such as SMTP, DNS, 
Telnet, POP3, etc. All of these, and many other standard services, uses 
"well-known" ports. For example, port 25 is used for SMTP and everyone has 
to know that, so that they can exchange email.

The standard Telnet port is 23. But if you load the Windows 95 or NT 
Telnet.exe, and choose "Remote host" from the "Connect" menu, you will see 
that you can specify the port. Try connecting to your web server on port 
80. You get nothing back, but when you type "GET", it returns an error 
code. Some devious person who knows HTTP better than I do could type in a 
proper HTTP command and get all sorts of useful low-level information with 
which to steer an attack.

We had a recent case where someone was telnet-ing on to our SMTP server and 
relaying invitations to examine a porn web site. The resulting emails 
apparently originated from our company, thus masking the offender's 
identity, but embarrassing us!

Neil

On Tuesday, August 11, 1998 7:57 AM, rick petersen 
[SMTP:rpetersen@RFWKLAW.com] wrote:
>
> TO UNSUBSCRIBE: email "unsubscribe ntsecurity" to majordomo@iss.net
> Contact ntsecurity-owner@iss.net for help with any problems!
> 
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>
> This is probably more on how to instead of security. The list keeps
> talking about blocking tcp and udp ports. I understand the concept of
> blocking ports and why but for the life of me I cannot figure out how to
> telnet into a specific port. Before I go blocking ports I would like to
> test the ease of access first.
> Thanks in advance for your support.
> Rick Petersen.