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Re: IP Session Hijacking And Spoofing
From: "simsjs" <sims () interex org>
Date: Mon, 25 Nov 2002 13:28:22 -0800

Charles,

Here is a clip from an article in network magazine:

Source routing can be strict or loose. Strict source routing lets a manager specify the path through all the routers to 
the destination. Return responses use the same path in reverse. Loose source routing lets managers specify an address 
that the packet must pass through on its way to the destination. It is loose source routing that aids an attacker.

You can find the entire article at http://www.networkmagazine.com/article/NMG20000517S0167

There is also a really good book called "Hackers Beware" that goes in detail over session hijacking and IP address 
spoofing that might help you understand a little better.

Glad I could help.

Jeff


*********** REPLY SEPARATOR  ***********

On 11/25/2002 at 1:12 PM charles lindsay wrote:

enlighten me.

How do you get the server to use source routing in its replies?  Source
routing tells the routers between you and the destination the next hops
for the packet.  As far as I am aware, there is no requirement that the
destination employ the reverse path in its replies.



From: simsjs [sims () interex org]
Sent: Friday, November 22, 2002 12:23 PM
To: LEHMANN, TODD; security-basics
Subject: Re: IP Session Hijacking And Spoofing

With IP Spoofing there is no need to guess the sequence number since
there is no session currently open with that IP address. The way that the
traffic would get back to you is by using source routing. This is where
you tell the network how to route the output and input from a session,
then you simply sniff it from the network as it passes by you. But you
have to make sure you put in a route that will both reach its destination
and pass through your own network.

As far as guessing the sequence numbering for session high-jacking, I
really have no idea, but there are programs that will attempt to guess
these for you. The one I am thinking of (whose name escapes me at the
time) will allow you to watch a session, reset a session, or hijack it.

Hope some of this helps.

Jeff


*********** REPLY SEPARATOR  ***********

On 11/19/2002 at 11:33 AM LEHMANN, TODD wrote:

I have read some documentation on IP Spoofing, and from what I have
read,
it
sounds like you must determine the sequence number of the host before
you
can spoof. However, I don't understand why you would have to determine
the
sequence if you are creating a new session with the host under a false
IP.
Wouldn't the creation of the new TCP session negotiate the sequence
number
at that time?

I also failed to understand how the traffic gets back to you if you are
telling it to respond to another host. Can someone shine some light on
this
for me?

When it comes to session high-jacking, how does one go about
determining
the
sequence number on a host that uses a random number seed to create the
sequence? Is it some form of complex algorithms or is it just
impossible
unless you create the session?

Todd Lehmann
Systems Analyst I
VPN Subject Matter Expert




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