Re: Tying a session to an IP address

[Rogan Dawes <discard () dawes za net>]

Actually, it is not so trivial to spoof a TCP connection long enough to 
get something useful from it. Especially an HTTP connection.

The original fear with spoofed connections was rlogin/rsh, which used IP 
addresses as authentication. The mechanism for exploitation was usually 
something like:

Send SYN packet from "authenticated/permitted" IP address.
Do not receive the SYN/ACK.
Send ACK packet, with a payload of something like

"echo '+ +' >> .rhosts"

Even if you do not receive a response, you have cracked the box.

This is still possible from some web apps, particularly those that allow 
you to execute admin functions if you come from a specific IP address, 
and don't use session cookies, etc.

BUT, the majority of apps on the Internet now require you to go through 
multiple levels in order to actually achieve something.

e.g. submit a GET to get a form to fill in, submit a POST with the 
values, submit a POST as a confirmation, etc.

It is not a simple as the rsh attack described above.

Personally, I think that tracking the IP address CAN add some value. It 
is not foolproof, and can cause problems in certain circumstances, but 
it helps to raise the bar where those circumstances do not apply to you.

Rogan

exon wrote:

> Paul Johnston wrote:
>
> > Hi,
> >
> > I'm interested in the merits of restricting a session to an IP 
> > address. I realise this isn't great security as often many users will 
> > appear to come from the same IP address (NAT, proxies, etc.) However, 
> > if you consider the case where an attacker uses an XSS vulnerability 
> > to steal the session ID, then the IP address restriction raises the 
> > bar considerably for an arbitrary remote attacker to exploit this. I'm 
> > worried that the IP address restriction wouldn't work for all users - 
> > e.g. if their ISP uses load-balanced web caches. Does anyone know how 
> > common such arrangements are in practice? Perhaps something to be done 
> > then is just check the top 16 bits of the IP address. This is likely 
> > to work for all such network arrangements and still raises the bar a 
> > lot for remote attacks.
> I'd say it doesn't do diddly squat to add to security, since it's 
> trivial to spoof ones address.
>
> > Does anyone here already restrict sessions by IP address?
> >
> > Regards,
> >
> > Paul

--
Rogan Dawes

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