Just finished reading about Surf Jacking from Ronald van den Heetkamp (and Sandro Gauci and Mike Perry), the demonstration movie that Sandro published really set in stone how interesting this vulnerability is. Sandro’s whitepaper describes the attack in detail, the primary attack scenario being the following:

• Victim logs into the secure web service at https://somesecurebank.com/.
• The secure site issues a session cookie as the client logs in.
• While logged in, the victim opens a new browser window and goes to http://www.example.org/
• An attacker sitting on the same network is able to see the clear text traffic to www.example.org.
• The attacker sends back a “301 Moved Permanently” in response to the clear text traffic to www.example.org. The response contains the header “Location: http://somesecurebank.com/”, which makes it appear that www.example.org is sending the web browser to somesecurebank.com. Notice that the URL scheme is HTTP not HTTPS.
• The victim’s browser starts a new clear text connection to http://somesecurebank.com and sends an HTTP request containing cookie in the HTTP header in clear text
• The attacker sees this traffic and logs the cookie for later (ab)use.

The first thing I did after reading this paper was to check my online banking, and I was relieved to see that the session cookies sent by the server were set to “Encrypted Only”.

…almost.

So, in the spirit of bringing ubiquitous two-factor authentication closer to the masses (because excuses are disappearing) I spent a few hours hacking together a Wordpress hack (plugin) that integrates Twitter’s direct message capabilities to provide a one time PIN when you log in to your Wordpress administration screen. The intent being that direct messages get sent to your mobile via SMS, hence SMS one time PIN generation, mimicking SMS PIN authentication as used by financial institutes.

Of course, by using this hack you introduce a number of dependencies, primarily that being Twitter’s service itself which doesn’t have a great track record, but also your mobile phone’s network. In addition, the fact that it is a hack, not a plugin, is also potentially a pitfall. The last issue is because I don’t actually know how to write a Wordpress plugin properly. Not for lack of trying, I can’t help it that one of the “pluggable” functions in Wordpress didn’t want to be overloaded. In fact, I’m not entirely sure that functions in version 2.6 can be overloaded(?).

I also have to admit that whilst the motivation is to introduce a second factor of authentication, such as a thing you know (your password) and a thing you have (your mobile phone), by using Twitter’s services you don’t actually need a mobile phone to get your PIN. So if you check your direct messages via the web interface, it’s actually a one-by-one factor authentication, not really two-factor, and we all know what 1 x 1 equals don’t we? But you get the point.

In regards to the good work done on the Phonefactor plugin I just want to comment that I was half way through this hack when I read about Phonefactor and it didn’t support calling Australia, so that meant I was out. The quality of their work is great though.

I’ll release the details soon..