Feature or Flaw?

Lance James lancej at securescience.net
Sun Jul 3 18:30:11 EDT 2005


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).

https://slam.securescience.com/threats/mixed.html

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
www.securescience.net
Author of 'Phishing Exposed'
http://www.securescience.net/amazon/
Find out how malware is affecting your company: Get a DIA account today!
https://slam.securescience.com/signup.cgi - it's free!


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