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
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?
Secure Science Corporation
Author of 'Phishing Exposed'
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