Defeating SSL using SSLStrip (Marlinspike Blackhat)

Marlinspike made a great presentation in Blackhat this year on how to subvert SSL (HTTPS) protection used bu major sites around the Internet for security. The interesting thing is that he does not really break the SSL protocol itself, but instead demonstrates that as HTTP is the entry point into any SSL communication, subverting HTTP allows a hacker to take control of the HTTPS communication as well.

Marlinspike also released the SSLStrip tool to automate this attack. Download SSLstrip from Moxie's website or from here. Using the SSLStrip tool Marlinspike was able to retreive over 130 usernames and passwords over a Tor network. These credentials were from sites such as Gmail, Yahoo, Linkedin, Paypal etc.

The way the SSLStrip tool works by:

1.  Does an MITM on the HTTP connection
2. Replaces all the HTTPS links with HTTP ones but remembers the links which were changed 
3. Communicates with the victim client on an HTTP connection for any secure link
4. Communicates with the legitimate server over HTTPS for the same secure link
   
5. Communication is transparently proxied between the victim client and the legitimate server
6. Images such as the favicon are replaced by images of the familiar "secure lock" icon, to build trust
7. As the MITM is taking places all passwords, credentials etc are stolen without the Client knowing

 Marlinspike also discusses other techniques such as homograph attacks to make a URL look like a legitimate one. The overall talk is very interesting. You can download the presentation slides here. The video posted below is of the actual Blackhat talk given by Marlinspike.

You can download a High Resolution video of the presentation here.
 

Vivek Ramachandran is a security evangelist and has been working in computer security related fields for the past 7 years. In 2007, Vivek spoke at world renowned conferences Defcon (WEP Cloaking Exposed) and Toorcon (The Caffe Latte Attack). The discovery of the Caffe Latte Attack was covered by CBS5 news, BBC online, Network World etc news agencies.In 2006, Vivek was announced as one of winners of the Microsoft Security Shootout contest held in India among 65,000 participants. He has also been a recipient of a Team Achievement at Cisco Systems for his work on 802.1x and Port Security modules on the Catalyst 6500 switches. Currently he spends all of his time maintaining Security- Freak.Net , SecurityTube.Net and is the co-founder of Axonize. Vivek, is a Bachelor in Electronics and Communications Engineering from the prestigious Indian Institute of Technology, Guwahati.You can contact him at vivek[at]securitytube.net