1. Internet Cache Pollution Attacks and Countermeasures Yan Gao, Leiwen Deng, Aleksandar Kuzmanovic, and Yan Chen Electrical Engineering and Computer Science Department Northwestern University

2. 2 Outline Motivation Pollution Attacks Evaluation of Pollution Effects Counter-Pollution Techniques & Evaluation Conclusion

3. 3 Motivation Caching has been widely applied in the Internet –Decrease the amount of requests in server side –Reduce the amount of traffic in the network –Improve the client-perceived latency Open proxy caches are used for various abuse-related activities Proxy caches themselves become victims –Little attention given to such attacks –Existing pollution attacks mostly on content pollutions on P2P systems

4. 4 Contributions Propose a class of pollution attacks targeted against Internet proxy caches –Locality-disruption (LD) attacks –False-locality (FL) attacks Analyze the resilience of the current cache replacement algorithms to pollution attacks Propose two cache pollution detection mechanisms –Detect LD, FL attacks, and their combination –Leverage data streaming computation techniques

5. 5 Outline Motivation Pollution Attacks Evaluation of Pollution Effects Counter-Pollution Techniques & Evaluation Conclusion

6. 6 Pollution Attack Scenarios (I) Attacking a web cache Attacking an ISP cache

7. 7 Pollution Attack Scenarios (II) ① ② ③ ④ ⑤ ⑥ ⑦ ⑧ Pollution attack against a local DNS server

8. 8 Pollution Attack: Locality Disruption ….... Cache ….... Cache Before attackAfter attack Popular files New unpopular files Goal: degrade cache efficiency by ruining its file locality Activities: continuously generate requests for new unpopular files

9. 9 Pollution Attack: False Locality ….... Cache ….... Cache Before attackAfter attack Popular files Bogus popular files Goal: degrade the hit ratio by creating false file locality Activities: repeatedly request the same set of unpopular files

10. 10 Outline Motivation Pollution Attacks Evaluation of Pollution Effects Counter-Pollution Techniques & Evaluation Conclusion

11. 11 Evaluation Methodology Discrete-event simulator –Multiple DoS behaviors –Multiple workload characterizing behaviors –Effects of access and local network capacities Workloads –P2P [K. Gummadi et al. ACM SOSP 03] –Web [F. Smith et al. SIGMETRICS 01] –NAT effects

12. 12 Cache Replacement Algorithms Least Recently Used (LRU) algorithm –Evict the least recently accessed document first Least Frequently Used (LFU) algorithm –Evict the least frequently accessed document first Greedy Dual-Sized Frequency (GDSF) algorithm –Consider the frequency of the documents –Allow smaller document to be cached first –Use dynamic aging policy

13. 13 Baseline Experiments Locality-disruption attacks Small percent of malicious requests can significantly degrade the overall hit ratio Total hit ratio = Including attackers’ requests and regular users’ requests Stealthy! (4%)

14. 14 Baseline Experiments False-locality attacks Total hit ratio is not a good indicator for attacks

15. 15 BHR(n)—byte hit ratio of regular clients without attacks BHR(a)—byte hit ratio of regular clients with attacks Byte damage ratio =

16. 16 Replacement Algorithms Locality-disruption attacks LRU and LFU are more resilient to attacks, but still can not protect cache from pollution

17. 17 Outline Motivation Pollution Attacks Evaluation of Pollution Effects Counter-Pollution Techniques & Evaluation Conclusion

18. 18 Detecting Locality Disruption Attacks Observations: –Low total hit ratio –Short average life-time of all cached files Design: –Detection: compute the average durations for all files in the cache –Mitigation: recognize the attackers

19. 19 Detecting False Locality Attacks Observations: –Clients who request a similar set of files residing in the cache –The repeated requests from the same IP to cached files Design: –Large number of repeated requests –Large percent of repeated requests Scalability: –Attacker-based detection: Bloom filter –Object-based detection: Probabilistic Counting with Stochastic Averaging (PCSA)

20. 20 Evaluation of Pollution Detection Results for false-locality attacks, more in paper For attacker’s file detection: True positive ratio =

21. 21 Realize the counter-pollution mechanisms Code and more details http://networks.cs.northwestern.edu/AE/ Implementation

22. 22 Conclusions Propose and evaluate two classes of attacks: locality-disruption and false- locality attacks Show that pollution attacks are stealthy, but powerful, and different replacement algorithms have different resiliency Propose and evaluate a set of scalable and effective counter-pollution mechanisms