Great Circle Associates Firewalls
(January 1995)
 

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Subject: re: Steve Bellovin's explanation.
From: "Daniel O'Callaghan" <danny @ www . unimelb . edu . au>
Date: Wed, 25 Jan 1995 19:06:04 +1100 (EST)
To: "Jon E. Price" <jon @ nytimes . com>
Cc: firewalls @ GreatCircle . COM, gordy @ nytimes . com
In-reply-to: <9501242328 . AA09537 @ mailgate . nytimes . com>


On Tue, 24 Jan 1995, Jon E. Price wrote:

> In Steve Bellovin's explanation on how a break-in can occur, he uses a tcp
> sequence number guesser as part of the break-in.
> 
> Why is a tcp sequence number guesser needed for the break-in?
> 
> If a machine B is running rsh and trusts machine A, why can't machine X just
> rsh to machine B spoofing the ip packets with A's  ip address?

This has already been mentioned in the last 12 hours.
B has to receive an acknowledgement of its SSN from A before it believes 
it has a connection.  Thus, A has to send the correct SSN ack to B.

Danny



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