RE: How to protect against cookie stealing?

["Dawes, Rogan (ZA - Johannesburg)" <rdawes () deloitte co za>]

Hi Death, :-)

The reason that one can't simply link the IP address to the session is that
there are ISP's, in particular AOL, that use cache arrays in a load
balancing configuration. So a request that goes through one proxy could be
followed by one that goes through a different one. 

Plus the fact that all users behind a single proxy would be seen to have the
same IP address.

A lot of people do not permit active content such as ActiveX objects, which
would be the only way to get the MAC address from the client. Besides which,
if the originating site can access this object through a script, so could
the attacker through an XSS, and supply that information to the attacker at
the same time as the sessionid.

I think this is the reason that nothing has been done about this problem:

* If the attacker can't XSS the user, they can't get the sessionid (unless
it is predictable, which is just stupid!), hence there is no problem. 

* If the attacker CAN XSS the user, then they can also get whatever other
information that they need to impersonate the user, except for the IP
address, which unfortunately, we can't rely on anyway, so we CAN'T do
anything about the problem.

Rogan

> -----Original Message-----
> From: .:[ Death Star]:. [mailto:deathstar () optonline net] 
> Sent: 24 July 2003 07:14 PM
> To: 'Dawes, Rogan (ZA - Johannesburg)'; 'Phil Cox'; 
> webappsec () securityfocus com
> Subject: RE: How to protect against cookie stealing?
>
>
> It is possible to associate each session ID with one IP address. In
> other words, you can make your script reject sessions 
> generated from the
> same IP (this is to avoid proxy's having the same IP address for
> different sessions and the same IP address requesting an existing
> session). This can be done by keeping an active table of 
> sessionID's and
> associated IP's.
>
> There is another solution, you can use both sessionID's and 
> cookies, so
> based on the IP address you would look for the cookie before 
> giving the
> user access control. The session ID will store 2 fields 
> (example userid
> and associated ip address) the cookie will hold other fields. 
> And u can
> use multiple sessions and multiple cookies that will be destroyed upon
> opening another page.
>
> Another solution is to create a script that will place an 
> object on the
> user machine this will allow your server not only to check 
> the ip (user
> gateway or proxy) but also the MAC and the local IP associated with it
> (could be the local IP of the user) and this info will also be
> associated with the gateway IP (public IP of the user).
>
> -----Original Message-----
> From: Dawes, Rogan (ZA - Johannesburg) [mailto:rdawes () deloitte co za] 
> Sent: Thursday, July 24, 2003 7:34 AM
> To: 'Phil Cox'; webappsec () securityfocus com
> Subject: RE: How to protect against cookie stealing?
>
> Well, there are only a limited number of things that one can do.
>
> The objective is to detect a change when a request is made. What
> information
> can we check against?
>
> * Source IP address - can change if behind a proxy server 
> array, doesn't
> protect against other users behind the same proxy
> * SSL sessionid - helps if you are using SSL, but this can 
> also change,
> I
> think. Particularly if the session is idle for a while?
>
> What else? Here is a sample request:
>
> POST http://localhost:8080/WebGoat/attack HTTP/1.0
> Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg,
> application/vnd.ms-excel, application/vnd.ms-powerpoint,
> application/msword,
> application/x-shockwave-flash, */*
> Referer: http://localhost:8080/WebGoat/attack
> Accept-Language: en-za
> Content-Type: application/x-www-form-urlencoded
> Proxy-Connection: Keep-Alive
> User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
> Host: localhost:8080
> Content-Length: 0
> Pragma: no-cache
> Cookie: JSESSIONID=5971DC264B764275ED682A353BD3D44C
>
> * Accept header - this is unlikely to change, but is easy to guess
> * Accept-Language - most likely to be en-us, but could vary. Worth
> adding,
> anyway.
> * UserAgent - one would have a reasonably good chance of 
> guessing this.
> A
> single incorrect guess should invalidate the session, although that
> would
> lead to DOS, perhaps.
>
> I would be inclined to make up a validation string comprised of a hash
> of
> (Accept: + User-Agent: + Accept-Language:) at the time of the user's
> login
> and check that on every request. If it ever changes, immediately
> invalidate
> the session, and warn the real user when they make a request with the
> correct string, that someone is trying to access their session.
>
> One could also check against the source IP as a precaution, 
> and at least
> flag sessions where the source IP changes as potentially being
> compromised.
> Quite what you would do with that, I'm not sure :-) 
>
> One flaw with this scheme, though: If the attacker manages to execute
> some
> script or other scheme to get the sessionid to their server, 
> they would
> be
> able to reap the headers as well :-( 
>
> Bang goes that theory. :-(
>
> That brings us back to source IP and SSL sessionid.
>
> IIRC, proxies are supposed to add an X-Forwarded-for header to the
> request
> headers. That could allow the server to track request that 
> occur across
> different proxies. However, an attacker that does not go 
> through a proxy
> would also be in a position to add such a spoofed header, and 
> they would
> be
> able to reap it from the request that delivered the sessionid. If they
> were
> behind a proxy, they could also add that header, but it might be
> overwritten
> by an upstream proxy?
>
> One could, over time, build up a list of IP addresses of 
> known proxies,
> and
> source ranges that they serve. That could work, but would take time to
> build
> up.
>
> Which leaves SSL sessionid. I'm not sure how reliable that is, and it
> doesn't help non secure sites.
>
> Which I think explains why no-one has done anything about 
> this problem!
> :-)
>
> Rogan
>
>
> > -----Original Message-----
> > From: Phil Cox [mailto:Phil.Cox () SystemExperts com] 
> > Sent: 24 July 2003 07:34 AM
> > To: webappsec () securityfocus com
> > Subject: How to protect against cookie stealing?
> >
> >
> > All,
> >
> > I have a question on how people are handling cookie stealing 
> > and session
> > segregation. For example, it is possible to use session 
> > cookie information
> > on multiple systems for most (all?) web applications I know 
> > of.  Here is a
> > scenario:
> >
> > When a user logs in he is assigned a BLAH_SESSIONID cookie 
> > which serves as
> > an authorization mechanism in the application.  The 
> > application  does not
> > associate the cookie to any session-specific information 
> > (e.g., source IP
> > address), so another user can also use the BLAH_SESSIONID 
> > cookie to access
> > the same information (over a different TCP/IP session) that 
> > the legitimate
> > user can.  If an attacker obtains, or guesses a valid 
> > BLAH_SESSIONID cookie
> > for an active session, he can use it without the user's 
> knowledge. For
> > example, I was able to execute the following command using an 
> > BLAH_SESSIONID
> > that was obtained from another session: Command on Linux box: 
> >
> >   # curl -b "BLAH_SESSIONID=0000FDHTNLVY5WX"
> > https://somesite.com/App/Function? 
> >
> >   Returns the page: (some portion of the returned page)
> >
> > Historically I have believed that having the application 
> associate the
> > BLAH_SESSIONID session cookie and its associated privileges 
> > with a specific
> > SSL session or source IP address would prevent this session 
> > stealing. But
> > recently I have been told that this solution does not work 
> > because of the
> > dynamic IP nature of MANY ISP's and the disassociation of 
> > SSL/HTTP. I would
> > like to know what others are doing to solve this problem, or 
> > if they are
> > just not solving it at all.
> >
> > Thoughts and comments are appreciated...
> >
> > Phil
>
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Important Notice: This email is subject to important restrictions, qualifications and disclaimers ("the Disclaimer") 
that must be accessed and read by clicking here or by copying and pasting the following address into your Internet 
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