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Efficient Client-Side Protection for CSRF Attacks: The Complete Roadmap

This document provides a comprehensive road map for automatic and precise client-side protection against Cross-Site Request Forgery (CSRF) attacks. It covers the background and example of CSRF vulnerabilities, the limitations of current countermeasures, main ideas for protection, and evaluation of assumptions regarding trusted origins. The text highlights the need for protection against unauthorized requests initiated by malicious domains and offers insights into filtering algorithms and trusted delegation assumptions. Additionally, it explores the challenges posed by non-malicious collaborations and the efficiency of the proposed countermeasures. The concept of origin trust and delegation is analyzed to ascertain potential vulnerabilities and mitigations. Key points include server-side modifications, client-side strictness, and the role of server proxies in safeguarding against CSRF attacks.

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Efficient Client-Side Protection for CSRF Attacks: The Complete Roadmap

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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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