1. 1 A Cautionary Note on Automatic Proxy Configuration 11 th December 2003 CNIS 2003 Andreas Pashalidis

2. 2 “There are probably thousands of organizations using automatic proxy configuration.” - Dr. Ian Cooper (editor of IETF “Web Proxy Auto-Discovery Protocol” Draft) e-mail excerpt, August 18 th, 2003.

3. 3 Agenda Why do we need it ? How does it work ? What can go wrong ? What else can go wrong ? Live demo ! Countermeasures. Conclusions.

4. 4 Agenda Why do we need it ? How does it work ? What can go wrong ? What else can go wrong ? Live demo ! Countermeasures. Conclusions.

5. 5 Why do we need it ?

6. 6 We want selection to occur automatically & in real time!

7. 7 Why do we need it ? To eliminate manual configuration.

8. 8 Agenda Why do we need it ? How does it work ? What can go wrong ? What else can go wrong ? Live demo ! Countermeasures. Conclusions.

9. 9 How does it work ? Just by ticking this checkbox!

10. 10 How does it work ?

11. 11 How does it work ?

12. 12 How does it work ?

13. 13 How does it work ?

14. 14 How does it work ?

15. 15 How does it work ?

16. 16 How does it work ?

17. 17 How does it work ?

18. 18 Agenda Why do we need it ? How does it work ? What can go wrong ? What else can go wrong ? Live demo ! Countermeasures. Conclusions.

19. 19 What can go wrong ?

20. 20 What can go wrong ? Interception Web spoofing

21. 21 What can go wrong ? Interception Web spoofing

22. 22 What can go wrong ? Interception Web spoofing

23. 23 What can go wrong ?

24. 24 What can go wrong ?

25. 25 Agenda Why do we need it ? How does it work ? What can go wrong ? What else can go wrong ? Live demo ! Countermeasures. Conclusions.

26. 26 What else can go wrong ?  The attack can be massive or selective.  The attack can be hidden. ( e.g. “use attack proxy only during weekends/for specific sites” )  Web browsers cannot display the configuration.

27. 27 What else can go wrong ? SSL/TLS Interception

28. 28 Agenda Why do we need it ? How does it work ? What can go wrong ? What else can go wrong ? Live demo ! Countermeasures. Conclusions.

29. 29 Agenda Why do we need it ? How does it work ? What can go wrong ? What else can go wrong ? Live demo ! Countermeasures. Conclusions.

30. 30 Countermeasures Authentication of proxy servers ( realistic? ) Firewalls (protection against outsiders). Use SSL/TLS to authenticate proxy, BUT New certificate type for this purpose. Change web browsers’ code path. Authentication failure = fatal error.

31. 31 Agenda Why do we need it ? How does it work ? What can go wrong ? What else can go wrong ? Live demo ! Countermeasures. Conclusions.

32. 32 Conclusion Think about these things before deploying an automatic proxy configuration solution.

33. 33 Thanks! Questions?