Great Circle Associates Firewalls
(November 1994)

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Subject: Telnet to SMTP
From: padgett @ tccslr . dnet . mmc . com (A. Padgett Peterson, P.E. Information Security)
Date: Fri, 11 Nov 94 08:39:09 -0500
To: "firewalls @ greatcircle . com"

>Would it not be possible to construct a 'smart' SMTP wrapper which tried some
>telnet option negotiation commands to detect telnet at the far end?  Would 
>this sort of thing violate SMTP?  Perhaps this could be incorporated into the 
>greeting message.

Certainly possible if the TELNET is using standard (e.g. VT) terminal
emulation since a "What Are You" request (<esc>[0c - 7 bit mode, CSI 0c - 8
bit mode, or <esc> Z - VT52 mode) should generate a response.

However TELNET does not *have* to use anything like this - for instance
FTP's PCTCP also offers the option TNGLASS which emulates a "dumb terminal"
with no intelligence. 

But then, this assumes the use of TELNET. It would be relatively simple for
anyone with access to the SMTP source to make it do anything desired. True,
few of the wannabees have bothered to learn C however, I have to consider what
a professional *could* do and that would not only look identical to an
SMTP process, it would think it *was* a SMTP process.

Be careful out there.

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