Re: anonymous messages


raj@PARIS.ICS.UCI.EDU
Tue, 08 Nov 88 09:33:54 -0800


I've been meaning to bring this topic up for quite a while so maybe this is
the time to do it. We all know (don't we?) that anyone can use telnet to
connect to the SMTP port on a machine and directly type in mail, thus making
it appear as though it comes from anyone they like. This has been taken
advantage of here at UCI by our undergrads a few times. (Enough that it
started becoming a bother!) It seems to me as if we could solve this whole
problem once and for all by simply requiring the originating port for SMTP
deliveries to be a privileged port ( < 512 ). As a matter of fact, we could
probably require the originating port to be 25 as well as the destination port.
(Afterall, a pair of IP addresses and port numbers fully specify a TCP
connection and why would you want 2 SMTP deliveries between the same pair of
machines at the same time? Anyway, if you do we can always make it simply
"any port number < 512.")

Now, before people start complaining about how this change isn't backward
compatible, etc., let me finish. For a period of a year or so everyone could
simply insert a header like:

X-Warning: This message arrived at xyz.site through an insecure port.

into any message originating from a non-privileged port. This way, people
would know to question the authenticity of that message. After everyone has
changed their SMTP delivery processes (a very minor change, afterall), we
could all remove this notice and actually reject connections from unprivileged
ports, but this may take quite a while (consider how long it's taking for some
places to change over to using nameservers!).

Well, what's wrong this idea? I figure there has to be something wrong with
it or else it would have been suggested long ago.

-----------------------------------------------------------------------------
Richard A. Johnson raj@ics.uci.edu (Internet)
UCI ICS Assistant Support Manager ucbvax!ucivax!raj (UUCP)
Postmaster / Network Services raj@tertius.ics.uci.edu (via Nameservers)



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