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

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Date: Fri, 07 Sep 2007 17:00:51 +0300
From: "Eddy Nigg (StartCom Ltd.)" <eddy_nigg@...rtcom.org>
To: Alexander Klink <a.klink@...ops.de>
Cc: full-disclosure@...ts.grok.org.uk, dev-security@...ts.mozilla.org,
	dev-tech-crypto@...ts.mozilla.org
Subject: Re: Firefox 2.0.x: tracking unsuspecting users
	using TLS client	certificates

Alexander Klink wrote:
> Here is how it works:
> - Because Firefox's standard configuration is to automatically choose a
>   TLS client certificate to be sent out, the certificate including
>   the personal data will now be sent out to any website that requests it.
>   Contrary to a typical cookie, this includes websites that are on a
>   completely different domain. The user will not notice this at all.
>   
Personally I'd prefer to have the default settings for "When a website 
requires a certificate" to be "Ask me every time". Specially if one has 
various certificates from the same CA, the clueless user logs in always 
with the first certificate on the list. Not really something one might 
expect.

However information stated in certificates signed by CAs isn't usually 
"private" and depending on the CA policy even published via directories 
and other different channels, so I'm not sure if this could be an 
invasion of privacy. Also tracking visitors can be done in different 
ways and doesn't have to be with cookies - again I'm not sure what's the 
difference. IChanging the default selection for certificate 
authentication could solve the problem you stated in any case. Perhaps 
file a bug for this?

>
> What other browsers do:
> - Firefox 1.5: Does not allow you to install a client certificate that
>   is from a CA which you don't trust. I still believe this was a decent
>   default setting.
>   
Are you sure there was a change? I don't remember this to be the case of 
pre-2.0 Firefox either.

-- 
Regards 

Signer:  	Eddy Nigg, StartCom Ltd. <http://www.startcom.org>
Jabber:  	startcom@...rtcom.org <xmpp:startcom@...rtcom.org>
Blog:  	Join the Revolution! <http://blog.startcom.org>
Phone:  	+1.213.341.0390

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