Sunday, June 21, 2009

Detecting MITM/Hacking Proxies Via SSL

There are several different ways for MITM/hacking proxies to handle SSL. They can create a self signed root cert that the attacker/user accepts once, they can do a per site snake oil cert, or they can simply downgrade the attacker/user to HTTP (a la Moxie’s sslstrip). Any of those work, and it’s kind of a matter of preference and circumstance as to which is better. But what if I’m running a site and I want to see if the user coming in is using a hacking proxy? There’s a few techniques to do that.

First of all there’s really not all that much you can do within SSL itself to create more than binary options (there are some exceptions to that rule, and I’ll post about that later) but those binary options are actually just enough. Let’s say I have several sites. One of which is a banking site. The others just have something as simple as a tracking pixel on them. Firstly, the time difference between when the user pulls the SSL certificate and actually instantiates the site might indicate whether they are going directly to the site or if they had to take some time to accept a self signed-per site certificate (a la Burp Suite).

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