[Full-disclosure] Firefox 2.0.x: tracking unsuspecting users using TLS client certificates

[Brendan Dolan-Gavitt]

It occurs to me that this could be used to good effect to track someone
using Tor across various domains you control. Most Tor users know to kill
JS, Flash, and are more than normally paranoid about cookies, but may not
think twice about accepting a client certificate. I'm CC'ing the Tor mailing
list to see what they think...

Can anyone see if this works through Privoxy and the other things in the
standard Tor bundle?

-Brendan

On 9/7/07, Eddy Nigg (StartCom Ltd.) <eddy_nigg at startcom.org> wrote:
>
>  Hi Alexander,
>
> Alexander Klink wrote:
>
> Granted, if this is a "real" CA. But if you use it like in my PoC not
> for the typical CA scenario, but for user tracking, you could put all
> kinds of data in the certificate.
>
>  That's right. Still I believe that the generation of a private key and
> issuance of the certificate is pretty "noisy". However I agree, some
> explanation would be better. Obviously on a CA, this process is explained at
> the web site, but as in your scenario, the user isn't supposed to know a lot
> about it....There is something to your claim....
>
> Tracking visitors in an unnoticed way over several domains is typically
> not as easy as this, I believe.
>
>  Well ,well... ;-)
>
> I've actually tested that again and it also works in Firefox 1.5 - and
> even "better" there, because the certificate installation does not show
> any dialog at all.
>
>  Right! In 1.5 no "Installation Message" appears, which in 2.0 has been
> corrected. I suggest to file a bug with the request to change the default
> settings for handling certificate authentication. Please send the bug
> number, so we can vote for it...
>
> --
>   Regards      Signer:  Eddy Nigg, StartCom Ltd. <http://www.startcom.org>
> Jabber:  startcom at startcom.org  Blog:  Join the Revolution!<http://blog.startcom.org>
> Phone:  +1.213.341.0390
>
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