mailing list archives
RE: Tying a session to an IP address
From: "Wolf, Yonah" <Yonah.Wolf () ujc org>
Date: Mon, 10 May 2004 10:26:49 -0400
I tried this approach a few years ago, and got stymied by the very same logic that you are posing - some web caches
are loadbalanced and although most of them can be programmed to take advantage of session stickiness, they don't. In
addition, we have even run into cases of Session-sharing - i.e. two people behind the same proxy get the same sessionID
- thereby further limiting the application of IP-based controls. Based on the way you are stating this problem, I am
going to assume that Server-level authentication and/or client certificates are not going to work - it sounds like we
are talking about a public web site.
In the past I have heard people wanting to use the HTTP_X_PROXY_FOR header to determine the internal ip address - but
that isn't standard across proxies TTBOMK.
Bear in mind - if two people are at a Wi-Fi hotspot, it is not inconceivable that one can intercept the other's
cookie and then use it to authenticate himself because he is coming from the same proxy.
From: Paul Johnston [mailto:paul () westpoint ltd uk]
Sent: Monday, May 10, 2004 9:14 AM
To: webappsec () securityfocus com
Subject: Tying a session to an IP address
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.
Does anyone here already restrict sessions by IP address?
Internet Security Specialist
Albion Wharf, 19 Albion Street,
Manchester, M1 5LN
Tel: +44 (0)161 237 1028
Fax: +44 (0)161 237 1031
email: paul () westpoint ltd uk
- Re: Tying a session to an IP address, (continued)