Towards Scalable and Robust Distributed Intrusion Alert Fusion with Good Load Balancing Zhichun Li, Yan Chen and Aaron Beach Lab for Internet & Security Technology (LIST) Northwestern University

2 The Spread of CodeRed

3 Distributed IDSes Distributed Intrusion Detection Systems (IDSes) –Crucial to identify large-scale attacks early –Robust to various scan techniques –Locate the attackers/zombies when spoofed –E.g, Symantec has 20,000 sensors in 180 countries General architecture –IDS nodes »Generate the alarms »Heterogeneous: host- or network- based –Sensor fusion centers (SFCs) »Fuse the alarms »A subset of IDSes or dedicated hosts

4 Desired Features of DIDS Infrastructure Scalability –15 million daily intrusion alerts reported to DShield Route only related alarms to the same SFC –Over 18,000 vulnerabilities found [CERT] –17,500 Win32 threats and their variants [Symantec] –Hierarchical fusion cannot scale w/ diverse alerts Distributed queries over multiple SFCs Good load balancing Attack resiliency

5 Outline Motivation CDDHT Design Features of CDDHT Evaluation Related Work Conclusion

6 Cyber Disease Distributed Hash Tables (CDDHT) General intrusion alert fusion framework, can plug-in any alert generation or alert fusion algorithm Part of the Router-based Anomaly/Intrusion Detection and Mitigation (RAIDM) system in LIST –High-speed network measurement with reversible sketches [IMC 2004, INFOCOM 2006] –Online flow-level anomaly/intrusion detection [IEEE ICDCS 2006] [IEEE CG&A, Security Visualization 06] –Router-based polymorphic worm signature generation[IEEE Symposium on Security and Privacy 2006]

7 CDDHT Design Leverage DHT systems –O(log(n)) hops distance where n is the # of nodes –O(log(n)) maintenance overhead for routing –Guaranteed success for deterministic routing –Fault-tolerant, robust, and DoS attack resilient –Becoming increasingly popular for serious use »Eg, eMule P2P system uses Kademila Primitives of CDDHT –Put (disease key, symptom report) –Summary report = Get (disease key)

8 Architecture of CDDHT Internet IDS Node ID : “0” + sha2(IP of the IDS) IDS + SFC Node ID: “1” + sha2(IP of the IDS) DIDS Coverage Attack Injected Attack Injected

9 Disease Key Design Challenge: fuse the vast, diverse symptoms from heterogeneous IDSes with different views –Key generation in a decentralized and deterministic manner Key idea: generate the disease keys which capture the uniqueness of certain attacks Focus on popular types of attacks Improve with features –Load balancing –Attack resilience

10 The Disease Key Currently, model four types of attacks Extensible design IntrusionIDCharacterization Field(s)Length DoS Attack000Victim IP (subnet)35 bits Scans0010 (for vertical & block scan) Source IP36 bits 1 (for horizontal & coordinated scan) Dest port # Src IP (horizontal scan)52 bits 0 (coordinated scan) Viruses/ Worms 0100 (for known)Worm ID (32bit)36 bits 1 (for unknown)Dst port #20 bits Botnets01100 (for DDNS entry)Botnet ID (32bit)37 bits 01 (for URL entry)Botnet ID (32bit)37 bits

11 Port Scan Disease Key Design Vertical scan and block scan –Source IP Horizontal scan and Coordinated scan –Scan port –Horizontal: + Source IP

12 Viruses/Worms and Botnets Disease Key Design Viruses/Worms –Known worms: hash of the worm name –Unknown worms: worm scan port # Botnets –Assume botnets use centralized C&C –IRC based bots: dynamic DNS –Web based bots: URL –Botnet ID = hash of the DDNS or URL

13 Outline Motivation CDDHT Design Features of CDDHT Evaluation Related Work Conclusion

14 Load Balancing Challenges to load balancing –Large key space in DHT –Highly skewed alert distribution Number of ports picked Number of subnets picked

15 Load Balancing II Proactive balancing with stable hot spots –Reduce key space of port # to 7 bits –64 buckets for 64 most popular port # –Remaining 64 buckets randomly assigned to other port # Balancing load of the key space –Node migration –Virtual node –Load-aware bootstrap Balancing load of single hot key –IDS alarm rate limiting Aggregation tree for large-scale attacks –Received alarms by the final SFC bounded by O(log(n))

16 Attack Resilience DoS resilience comparison with hierarchical model –Proved the average number of alerts unreachable to their corresponding SFCs given one node loss »Hierarchical DIDS: O(log (n)) »CDDHT: O(1) More in the paper –Authenticity of alarms –Dealing with compromised nodes

17 Outline Motivation CDDHT Design Features of CDDHT Evaluation Related Work Conclusion

18 Methodology Implementation –Preliminary CDDHT system based on Chord simulator –Event-driven simulation »Each alarm is an event with a timestamp from certain IDSes Datasets –DShield firewall logs (Jan. 2004) –Results from each day’s data are similar –Use January 2 nd 2004 as illustration »25 million scan logs from 1,417 providers »Randomly choose 10% to be SFCs Scan typeVerticalHorizontalBlockCoordinated # of scans

19 Evaluation Metrics Fusion effectiveness –100% due to deterministic routing of CDDHT Load balancing –Consider number of alerts received at each SFC –Maximum vs. mean ratio (MMR) –Coefficient of variation (CV)

20 Proactive Balancing with Stable Hot Ports Proactive load balancing can reduce CV by 60% and reduce MMR by 40%

21 The Load Variation Comparison Between Hierarchical Scheme and CDDHT Median, 10- and 90- percentile of 10 runs CDDHT with proactive balancing (PB) and virtual nodes (VN) Compared with Hierarchical schemes, CDDHT reduces the MMR by a factor of 5.5 and CV by a factor of 5.2 Hierarchical CDDHT CDDHT w/ PB CDDHT w/ PB+VN Hierarchical CDDHT CDDHT w/ PB CDDHT w/ PB+VN

22 Outline Motivation CDDHT Design Features of CDDHT Evaluation Related Work Conclusion

23 Related Works CDDHTCentralized /Hierarchic al Model Publish/ Subscribe Model P2P Querying Failure/ attack resilience HighLowHigh Fusion overhead Low HighLow Query overhead Low High WormShield uses DHT specifically to find popular content fingerprints as worm signatures, but does not work for polymorphic worms

24 Conclusion Large number and diverse alerts from many distributed IDSes calls for efficient fusion of these alerts CDDHT: Cyber Disease DHT –Efficient route alarms of different intrusions to different SFCs –Highly scalable and robust –Good load balancing –High attack resilience Future work –Disease keys for more types of attacks and querying of CDDHT

Backup Slides

26 Introduction to DHT DHT (Distributed Hash Table): An infrastructure that enables the distribution of an ordinary hash table onto a set of cooperating nodes KeyObject 0x2535“Apple” 0x2353”Banana” 0x3978”Peach” 0x9123”Strawberry” 0x7234”Grape” 0x5942”Watermelon” node A node D node B node C Each node only stores part of the hash table Basic operations –Put(Key, Object) : From Key to find the corresponding node via DHT routing and store the Object on the node –Object=Get(Key) : From Key to find the corresponding node via DHT routing and retrieve the Object from the node

27 Introduction to DHT II Different DHT systems –Chord –CAN –Pastry –Tapestry -Kademlia -Kademia has been used in eMule P2P software Chord DHT routing DHT routing –Distributed and deterministic routing –The max hops to find the node corresponding to a key is bounded by O( log (n) )

28 DoS Attack Disease Key Design Most DoS attack target specific IP addresses (the server) or the subnet (Bandwidth consuming attack) But the victim IP (subnet) can be destination or source (in backscatter) Other parts all can be variants

29 Related Works Centralized/Hierarchical Model Publish/subscribe Model –O(n 2 ) communicate vs. O(n) P2P Query –Scalability with frequent fusion

30 Attack Resilience DoS resilience comparison with hierarchical model –Proved the average number of disconnected nodes given one node loss »in a k-way hierarchical DIDS is O(log (n)) »but the DHT based is O(1). Authenticity of alarms –Valid the source subnets of IDS by Whois and BGP tables –Use PKI to verify the messages send by IDSes/SFCs

31 Attack Resilience II Dealing with compromised nodes –IDS nodes »Voting the importance of the results by # of IDSes, IP coverages »Probability based verification for alarm aggregation –SFC nodes »The “trust but verify” principle »Envision that there is a centralized authority randomly check the fusion results for the SFCs

32 Proactive Balancing with Stable Hot Ports Use 7 bits encoding, can reduce MMR by 60% and reduce CV by 40%

33 Dynamic of Load Variation over Time MMR for CDDHT is much smaller and smoother CV also get better