> 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?
You never do create a session. A session requires that you have a three-way handshake, which you can't have when the packets being sent from the victim are going to the address you are spoofing and not to you. > 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? That's the trick; they don't get back to you. :) > 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? Yes, it is something very complex, to be sure. There are tools for doing it, and the degree of difficulty is based on the method used to create pseudo-random numbers on the target OS. This is what you are seeing when you nmap a host with the -O switch and get back, "Random Positive Increments: GOOD LUCK!". It is saying that is going to be very hard to predict sequence numbers on that host for doing these sorts of attacks. --danielrm26
