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EV SSL Browser Based Attack


There has been some recent coverage about a security flaw in EV SSL certificates. I think it is worth pointing out the facts (as I see them) of this "flaw". 
 
Firstly there is no security flaw in Extended Validation SSL Certificates. The certificates still function correctly.
 
This flaw is actually a "Man in the middle" attack. It is a fairly common type of attack which has been known for some time. However to be able to attempt the attack there are a number of requirements the attacker needs to fulfil. They must have an existing certificate (this can be a simple domain validated certificate). They must also be able to poison the users DNS records. 
 
The attack is supposed to work by the main domain presenting the EV enabled green address bar for the main site and then the attacker loading iframe content within the website which is secured by a non EV certificate. The iframe content would be controlled by the attacker but the green address bar would still be shown. 
 
To complete the attack the attacker needs to do a number of steps: 
 
The attacker must find a website which utilises an iframe or some form of widget included from a different URL. For example the website https://www.servertastic.com could have an iframe login page loaded from www.mylogin.com (it doesn't this is just an example!)

The attacker would poison the DNS records to point www.mylogin.com to their own webserver. Doing so they could then collect your login data and other information they require. 
 
For this to work the attacker needs to secure the content loaded in the iframe with an SSL certificate so the browser still shows the green address bar from the main frame (www.servertastic.com). This is where I believe the attack does not work. 
 
The attacker would need to obtain a DV certificate for www.mylogin.com which they can not do because they do not own www.mylogin.com. Alternatively they could hijack www.mylogin.com and redirect it to www.attackersdomain.com which they do own and does have a certificate.

But they would still not be able to present a valid certificate for www.mylogin.com and therefore the browser will display a SSL warning error either "mismatched SSL domain", "mixed SSL and non-SSL content" or "redirect to a non-secure SSL warning". 
 
The attack could succeed if the attacker was able to inject code into the EV enabled website (which would make the flaw code based rather than SSL/browser based) or the end user had disabled all the SSL related warnings within their browser. Plus the user would have to be accessing the website via a poisoned DNS cache made possible by an open wi-fi hotspot for example. 
 
Therefore at the moment I do not believe this is a flaw in SSL or browsers. It is just hitting the headlines because it is in relation to EV certificates. If the end user just followed basic security practices such as not accessing unknown internet access points and not disabling the security settings in their browser then this attack should not be possible. 
 
I have not yet seen a demonstration of the "attack" and therefore I may not be understanding the process correctly. Therefore my views may 
be completely incorrect.

Posted by Andy Gambles 

Comments (13)

Jul 23, 2009
WarrenAshcroft said...
Why would they need to use DNS poisoning, surely an attacker could just find an XSS vulnerability to insert their own iframe on the EV page to whichever https URL they control?
Jul 23, 2009
WarrenAshcroft said...
...or change the URL or any existing iframe already on the EV page - this way it gets around having to use DNS poisioning and avoids the mismatched domain issue in your (correct) theory. The solution to this is that browsers should not behave like EV (green) unless all loaded page content is EV.
Jul 23, 2009
Andy Gambles said...
All the articles I have read have discussed iframe DNS poisoning. The XSS vulnerability is more likely to work. But then this is down to the website developers security rather than a flaw in EV / browsers as a lot of articles seem to be suggesting.
Jul 23, 2009
stephenduncan said...
Excellent posting. THANK YOU for the article. It would seem to me that a weak point in the process might be the ability to get a DV certificate nefariously, not a weakness in EV!
Jul 23, 2009
Andy Gambles said...
@warrenashcroft how would you change the iframe URL without access to the website code other than via some form of XSS I can not see it is possible.
Jul 23, 2009
Andy Gambles said...
@stephenduncan This is the only way I can see this as being really effective by being able to obtain a DV cert via some way. I know some SSL certificate authorities who do not complete the domain validation for SSL resellers instead they rely on the reseller to verify the ownership.
Jul 23, 2009
WarrenAshcroft said...
That's what I said, they would need an XSS vulnerability to be able to do it. Both method are equally difficult, and the original would give you the name mismatch.
Jul 23, 2009
Andy Gambles said...
@warrenashcroft Yeah this is why I think the whole talking about EV flaw or attack is over the top. More about DV certificate miss-issuance and XSS.
Jul 27, 2009
Stuart said...
Ok am currently getting an EV SSL cert at the moment for a site, as you said theres warning's in browsers if anything is wrong, have seen many emails in the late that try to fool paypal.com site which uses EV SSL any attempt ive seen always has a warning on screen some of these sites have tried using Iframe method however DV Certs are normally only issued to the domain they are intended for playing around with the code will in most cases break the cert, Unless someone has alot of time on there hands it's gona be quiet hard to do anyway. Nothing better than manually typing the address in yourself and actually look at where your entering details if someone dont then I would find that lazy esp in todays world you should check anything that requires anything personal going in to a browser.
Jul 27, 2009
Andy Gambles said...
Stuart thank you for taking the time to comment. If you want help with your EV certificate let us know http://bit.ly/fyFVD
Sep 01, 2009
Ultima Hosts said...
Has Verisign stepped in with any comments on this EV flaw?
Sep 01, 2009
Andy Gambles said...
As per the article there is no flaw in EV certificates.
Sep 01, 2009
Allen Kelly said...
Tim Callan, vice president of product marketing at VeriSign, responds to these Black Hat presentations in his new SSL blogpost:

https://blogs.verisign.com/ssl-blog/2009/07/busy_day_at_black_hat.php

He fills some of the holes that these researchers dug.

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