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Date: Fri, 6 Oct 1995 19:28:25 -0700
From: "Russell L. Carter" <rcarter@geli.com>
Message-Id: <199510070228.TAA27362@geli.clusternet>
To: chuckr@eng.umd.edu, terry@lambert.org
Subject: Re: Fiskars UPS support...
Cc: freebsd-hackers@FreeBSD.ORG
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|> I don't find 'privileged ports' in my trusty O'Reillly TCP/IP book, could 
|> you give me a reference?  I just don't see, right now, what would stop 
|> someone with a packet sniffer, finding how I communicate, then spoofing 
|> the remote.  I know how to set up connections, I'm wondering about 
|> security, and how much is enough, when I'm talking about something that 
|> can shut down the machine.
|
|man rresvport
|
|A port in the range 1-1023 can only be allocated by root.  That is,
|those ports can only be answered by a Trojan Horse if your monitoring
|system has been fully compromised.
|
|The spoofing is prevented because the systems that can be spoofed make
|the connection to the monitoring system.  That means someone can not
|pretend to be the monitoring system and sending a failure warning and
|cause a shutdown because connections are not made in that direction.
|
|The worst that someone can do is register with the monitoring system
|and get powerfail notifications, and then only if you don't put
|restrictions on who is allowed to connect to the monitoring system
|in the first place (ie: it should be inside your firewall in any case).
|
|
|					Terry Lambert
|					terry@lambert.org

You might also have a look at Stevens' `Unix Network Programming'
Chapter 6, section 8. "Reserved Ports".

Besides the SMM, this book and the TCP/IP Illustrated books should
be required for FreeBSD hackers, dontchathink?  Maybe WC could
go into the bookseller business, or fix up promotional deals
with Computer Literacy.

Russell