Yan Chen Lab for Internet and Security Technology (LIST) Dept. of Electrical Engineering and Computer Science Northwestern University Intrusion Detection and Forensics for Self-defending Wireless Networks

Security Challenges in GIG Wireless Networks In addition to sharing similar challenge of wired net –High speed traffic (e.g., WiMAX) –Zero-day threats –Lack of quality info for situational-aware analysis: attack target/strategy, attacker (botnet) size, etc. Wireless networks are more vulnerable –Open media Easy to sniff, spoof and inject packets –Open access Hotspots and potential large user population

Self-Defending Wireless Networks Net-based adaptive intrusion detection & mitigation –Scalable traffic monitoring & anomaly detection (done in yr1) –Polymorphic zero-day worm signature generation (done in year 2) –Automated analysis of large-scale botnet probing events for situation aware info (mostly done, focus of this talk) Proactive vulnerability analysis and defense of wireless network protocols (done) –Found a class of exception triggered DoS attacks –Easy to launch: no need to change MAC –Efficient and scalable: small traffic, attack large # of clients –Stealthy: cannot be detected w/ current IDS/IPS

4 Generally Applicable Countermeasures schemes also proposed.

Accomplishments on Publications Six conference and three journal papers “Using Failure Information Analysis to Detect Enterprise Zombies", to appear in the Proc. of SecureComm "POPI: A User-level Tool for Inferring Router Packet Forwarding Priority", ACM/IEEE Transaction on Networking (ToN), "FAD and SPA: End-to-end Link-level Loss Rate Inference without Infrastructure", in the Journal of Computer Networks, “Exception Triggered DoS Attacks on Wireless Networks”, the 39th IEEE/IFIP International Conference on Dependable Systems and Networks (DSN), "BotGraph: Large Scale Spamming Botnet Detection", USENIX Symposium on Networked Systems Design and Implementation (NSDI) "Towards Efficient Large-Scale VPN Monitoring and Diagnosis under Operational Constraints", IEEE INFOCOM (main conference), “Automating Analysis of Large-Scale Botnet Probing Events”, ACM Symposium on Information, Computer and Communications Security (ASIACCS), “Pollution Attacks and Defenses for Internet Caching Systems”, in Journal of Computer Networks, "Botnet Research Survey," the 32nd Annual IEEE International Computer Software and Applications Conference, 2008 Collaborated publication with Dr. Keesook Han from AFRL Resulted from joint research on botnet. Obtain binary/source from Dr. Han Plan to use the testbed developed at AFRL

Automating Analysis of Large-Scale Botnet Probing Events Zhichun Li, Anup Goyal, Yan Chen and Vern Paxson* Lab for Internet and Security Technology (LIST) Northwestern University * UC Berkeley / ICSI

7 Motivation Administrators IPv4 Space Enterprise Botnets Does this attack specially target us? Can we answer this question with only limited information observed locally in the enterprise?

8 Motivation Can we infer the probe strategy used by botnets? Can we infer whether a botnet probing attack specially targets a certain network, or we are just part of a larger, indiscriminant attack? Can we extrapolate botnet global properties given limited local information?

9 Agenda Motivation Basic framework Discover the botnet probing strategies Extrapolate global properties Evaluation Conclusions

10 Botnet Probing Events Big spikes of larger numbers of probers mainly caused by botnets

11 System Framework See the paper for subtle system details.

12 Agenda Motivation Basic framework Discover the botnet probing strategies Extrapolate global properties Evaluation Conclusions

13 Discover the Botnet Probing Strategies Use statistical tests to understand probing strategies –Leverage on existing statistical tests Monotonic trend checking: detect whether bots probe the IP space monotonically Uniformity checking: detect whether bots scan the IP range uniformly. –Design our own Hitlist (liveness) checking: detect whether they avoid the dark IP space Dependency checking: do the bots scan independently or are they coordinated?

14 Design Space

15 Hitlist Checking Configure the sensor to be half darknet and half honeynet Use metric θ = # src in darknet/ # src in honeynet. Threshold 0.5

16 Agenda Motivation Basic framework Discover the botnet probing strategies Extrapolate global properties –Global scan scope, total # of bots, total # of scans, total scan rate for each bot Evaluation Conclusions

17 Extrapolate Global Properties: Basic Ideas and Validation Observe the packet fields that change with certain patterns in continuous probes. –IPID: a packet field in IP header used for IP defragmentation –Ephemeral port number: the source port used by bots –Increment for a fixed # per scan Validation –IPID continuity: All versions of Windows and MacOS –Ephemeral port number continuity: botnet source code study Agobot, Phatbot, Spybot, SDbot, rxBot, etc. –Control experiments with NAT

18 Estimate Global Scan Rate of Each Bot Count the IPID & ephemeral port # changes –Recover the overflow of IPID and ephemeral port number –Estimate the rate with linear regression when correlation coefficient > 0.99 –Counter overestimation: use less of the two T IPID

19 Extrapolate Global Scan Scope IPv4 Space Botnets Total scans from bot i : scan rate R i * scan time T i = 100*1000=100,000 bot i n i =100 Aggregating multiple bots Local/global ratio

20 Extrapolate Global # of Bots Idea: similar to Mark and Recapture Assumption: All bots have the same global scan range Bots Total M=4000 First half m1=1000 Observed by both m12= 250 Second half m2=1000 M=m1*m2/m12 M m1m2 m12

21 Agenda Motivation Basic framework Discover the botnet probing strategies Extrapolate global properties Evaluation Conclusions

22 Dataset Based on a 10 /24 honeynet in a National Lab (LBNL) 293GB packet traces in 24 months ( ) Totally observed 203 botnet probing events –Average observed #bots/event is 980. Mainly on SMB/WINRPC, VNC, Symantec, MSSQL, HTTP, Telnet Size of the system: 13,900 lines: Bro (6,000), Python (4,000), C++ (2,500), R (1,400)

23 More than 80% uniform scanning Validate the results through visualization and find the results are highly accurate. Property Checking Results

24 Extrapolation Results Most of extrapolated global scopes are at /8 size, which means the botnets do not target the enterprise (LBNL). Validation based with DShield data –DShield: the largest Internet alert repository –Find the /8 prefixes in DShield with sufficient source (bots) overlap with the honeynet events Due to incompleteness of Dshield data, 12 events validated –Calculate the scan scope in each /8 based on sensor coverage ratio.

25 Extrapolation Validation Define scope factor as max(DShield/Honeynet,Honeynet/DShield) CDF of the scope factor 75% within 1.35 All within 1.5

26 Conclusions Develop a set of statistical approaches to assess four properties of botnet probing strategies Designed approaches to extrapolate the global properties of a scan event based on limited local view Through real-world validation based on DShield, we show our scheme are promisingly accurate

27 Backup

28 Event size distribution

29 Extrapolate the scope Local/global ratio Probing time window Estimate global probing rate Probes observed locally

30 Monotonic trend checking Goal: detect whether the bots probe the IP space monotonically –E.g. simple sequential probing Technique: –Mann-Kendall trend test –Intuition: check whether the aggregated sign value (sign(A i+1 -A i )) out of the range of randomness can achieve. –When most (>80%) senders in an events follow trend we label the events follow trends

31 Uniformity Checking Goal: detect whether the botnet scan the IP range uniformly. Technique: –Chi-Square test –Intuition: put address into bins. The scan observed in each bin should be similar. –Significance level of 0.5%

32 Dependency Checking Goal: Is the bots try to get out each other’s way? Idea: account the number of address receive zero scan and comparing with confidence interval of the independent random case.