full-disclosure - Re: Firefox 2.0.x: tracking unsuspecting users using TLS client certificates

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Message-ID: <46E18B0F.1040301@lava.net>
Date: Fri, 07 Sep 2007 07:31:59 -1000
From: Peter Besenbruch <prb@...a.net>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: Firefox 2.0.x: tracking unsuspecting users
 using	TLS client certificates

With apologies to Alexander. I keep forgetting that replying to full 
disclosure messages sends an e-mail to him, and not the list. Here is my 
reply to the list:

Alexander Klink wrote:
 > ... I realised that you can do something with Firefox 2.0.x that
 > you could not do with Firefox 1.5.x: track an unsuspecting user
 > using TLS client certificates.

...

 > Proof of Concept:
 > - http://0x90.eu/ff_tls_poc.html

So, one can use certificates as a kind of super-cookie. You mention in a 
follow-up message that all kinds of information can be stored in a 
certificate. With cookies, a third party advertiser can place a cookie 
and track you across sites, building up a profile of your interests.

While I can see the same use here, it seems you are saying anyone could 
have a look at certificates on your system, while cookies generally are 
limited to viewing by the issuing domain. What I don't understand is if 
there is a simple of knowing what certificate to ask for? For this to be 
useful, that would be pretty important. Another question, is it possible 
to issue a "give me all your stored certificates" command? The follow-on 
link to Apache's cert-export page can't seem to do that. I made two 
certs and the cert-export page grabbed that last one.

Oh well, time to change Firefox's default certificate handling.
-- 
Hawaiian Astronomical Society: http://www.hawastsoc.org
HAS Deepsky Atlas: http://www.hawastsoc.org/deepsky

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