Hi all,

I wanted to introduce something that has probably been known for some time now, but has never been really addressed due to possible conflicting views of how SSL certificates should work, and where the CA's should (or should not) fit in. As we all know, the recent attention to the phishing threat vector has spawned some interesting views of how we look at certain responses that a web browser might appropriate in regards to certain conditions set by the server. Some of these include the recent "javascript dialog" box vulnerability, since there are requests that a javascript dialog box should display it's origin, etc... (see http://secunia.com/multiple_browsers_dialog_origin_vulnerability_test). In light of that, I thought it might be relevant to address a question that's been on my mind, and figure that the cryptography list may be the best place to find the answer. (the answer is 42, just kidding).

I've set up a site that requires a bit of imagination since I don't wish to expose any financial institutions (bankone is just a random example that I chose) that may be vulnerable to cross-user attacks, but I can tell you that this discovery of impact was done within an audit that explicitly demonstrated a problem. Also, I use a thawte signed certificate, so some mozilla browsers do not seem to regard it as a valid CA, please ignore that if you get a warning, as it is only a distraction of the real problem (aka, if it were a verisign cert it would not warn).


This site is set so that there is a frame of https://www.bankone.com inside my https://slam.securescience.com/threats/mixed.html site. The imaginative part is that you may have to reverse the rolls to understand the impact of this (https://www.bankone.com with https://slam.securescience.com frame -> done via cross-user attacks trivially). At the bottom you will see the securescience.com certificate, but no indication of the bankone certificate. You will also not get any warnings due to the fact that the bankone certificate is validly signed by a CA. With the Cross-User threat vector, a phisher can easily use a validly signed Cert to perform a site takeover with no warning that an outside (the domain) certificate exists within the site. The lock does show that it's secure, and there are no indications that this site should not be "trusted" according to the rules that are dispersed to the mainstream public. Unfortunately, this "Mixed" attack in a cross-user scenario could be encrypting/decrypting the login page with the attacker cert and no one is the wiser without heavy inspection of the source code.

Feature, or flaw?

Best Regards,
Lance James
Secure Science Corporation
Author of 'Phishing Exposed'
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