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Automatic and Precise Client-Side Protection against CSRF Attacks

Automatic and Precise Client-Side Protection against CSRF Attacks. Road Map. Background / Example Problem of Current Countermeasures Main Ideas Evaluation the Assumption. Background. CSRF: Cross Site Request Forgery

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Automatic and Precise Client-Side Protection against CSRF Attacks

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  1. Automatic and Precise Client-Side Protection against CSRF Attacks

  2. Road Map • Background / Example • Problem of Current Countermeasures • Main Ideas • Evaluation the Assumption

  3. Background • CSRF: Cross Site Request Forgery • Two domains A and B. Content of origin B initiate requests to origin A, and the browser will treat these requests as being part of the ongoing session with A. • The problem is: if the session with A is authenticated session, B can initiate privileges requests to A, without the user being involved.

  4. Example <html> <body> <form action=”https://mdsec.net/auth/390/NewUserStep2.ashx” method=”POST”>Chapter 13 Attacking Users: Other Techniques 505 <input type=”hidden” name=”realname” value=”daf”> <input type=”hidden” name=”username” value=”daf”> <input type=”hidden” name=”userrole” value=”admin”> <input type=”hidden” name=”password” value=”letmein1”> <input type=”hidden” name=”confirmpassword” value=”letmein1”> </form> <script> document.forms[0].submit(); </script> </body> </html> POST /auth/390/NewUserStep2.ashx HTTP/1.1 Host: mdsec.net Cookie: SessionId=8299BE6B260193DA076383A2385B07B9 Content-Type: application/x-www-form-urlencoded Content-Length: 83 realname=daf&username=daf& userrole=admin&password=letmein1& confirmpassword=letmein1

  5. Problem of Current Countermeasures • Server-Side: • Require server-side modifications on source code level and it may take a very long time. • Client-Side: • Too strict • Server-Proxy: • Have not published

  6. Main Idea • Except expected request, client-side state is stripped from all cross-origin requests. • Expected Request: A cross-origin request from A to B is expected if B previously delegated to A. • B delegates to A if • B issues a POST request, or • B redirects to A with parameters Conclusion: When origin A trying to send request to origin B, client-side state is stripped, Unless, B trust A.

  7. Main Idea • Two reasons: • Non-malicious collaboration scenarios follow this pattern. • It is hard for attacker to bypass the countermeasure.

  8. Filtering Algorithm

  9. Evaluating the Trusted-Delegation Assumption • Assumption: An origin won’t be attacked by a “trusted” origin. • Origin A trust origin B only if A post message to B or A redirect to B with parameters. • 10 out of 23 hundred origins are left unprotected by the countermeasure.

  10. Redirecting Search Engines http://www.google.com.hk/url?sa=t&rct=j&q=books&source=web&cd=3&ved=0CFAQFjAC&url=http%3A%2F%2Fwww.bookdepository.co.uk%2F&ei=Y_2RT7LLApKQ8wSn8bDvAw&usg=AFQjCNF8hAxvKCjeraYiftw74cony0jTkQ GET Redirect [Trust] http://www.bookdepository.com/

  11. URL shorteners http://www.malicious.com/2012/04/20/world/meast/bahrain-f1-explainer/index.html?hpt=wo_c2 https://bitly.com/ http://bit.ly/IFLzqI Redirect http://www.malicious.com/2012/04/20/world/meast/bahrain-f1-explainer/index.html?hpt=wo_c2

  12. Questions

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