Firefox Remote Compromise Technical Details

Before I start, I need to say that this thing has been patched on Mozilla's server. If you take a loo
k at any of the extension install
 pages on their site, you will see that the install function has a bunch of random letters and number
s after it. Even though this
 would probably be an easy thing to bypass, I am not going to attempt it because of the uselessness o
f such a bypass. A patch is already
 in development and so any more work going into fine-tuning this exploit would be a waist of time.

There are three core vulnerabilities being used in my example. A friend of mine (Michael Krax, http:/
/www.mikx.de) helped me with
 the research. 

To understand why the example works, one must understand the basics of how Firefox works. Everything 
you see in firefox is essentially
 a webpage being rendered by a compiler. This is what the gui is made of, and this is why firefox is 
so easy to customize. However,
 it also allows for some security bugs. If one could get one of the chrome pages to request a javascr
ipt:[script] url, that individual
 would be given complete access to the system because chrome urls are given full rights in firefox. M
y example works by tricking the
 addon install function into displaying an icon with a javascript url.

However, this would not be enough to compromise the system. By default, the install feature only work
s when called from a page within
 update.mozilla.org or addon.mozilla.org. Therefore, another (cross site scripting) vulnerability had
 to be found to call the install
 feature from mozilla.org. This vulnerability navigates to a javascript page and displays a link (poi
nting to a mozilla.org page)
 within a frame that follows the user's cursor. After the user clicks, the link is navigated to, whic
h fires the onload event. This
 is a buggy event in Firefox because with it we can now access certain parts of the window object tha
t we shouldnt, such as the history
 object. After the page loads, we use the history object to navigate backwards to the javascript page
. The javascript is executed
 again, now from update.mozilla.org because when we navigated backwards, we essentially navigated to 
a javascript:[script] page. Now
 we call the install addon feature, which displays a dialog with det
 ails of the requested addon, including an image with a specified image. This image points to a javas
cript:[script] url, which gets
 executed in the context of chrome. Now we have compromised the system :)

Whew, that was quite a mouthful.

I am still trying to gather all the details as to how my research was leaked, but recent conversation
s are leading me to believe that
 it was a misplacement of trust, not a server compromise. However, I do not want to jump to conclusio
ns too quickly, as this will
 only lead to more problems. That's all I will say about that subject, as I don't want to offend anyb
ody.

Also, I would like to let everyone know that this is not the only vulnerability that Mikx and I have 
found. We still have a couple
 of tricks up our sleeves, and you can be sure that we will not make the same mistake twice. 

If you want to see the original PoC, here is the url:
http://greyhatsecurity.org/vulntests/ffrc.htm

Paul
Greyhats Security
http://greyhatsecurity.org
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