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Machine Learning for Network Anomaly Detection

Machine Learning for Network Anomaly Detection. Matt Mahoney. Network Anomaly Detection. Network – Monitors traffic to protect connected hosts Anomaly – Models normal behavior to detect novel attacks (some false alarms) Detection – Was there an attack?. Host Based Methods. Virus Scanners

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Machine Learning for Network Anomaly Detection

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  1. Machine Learning for Network Anomaly Detection Matt Mahoney

  2. Network Anomaly Detection • Network – Monitors traffic to protect connected hosts • Anomaly – Models normal behavior to detect novel attacks (some false alarms) • Detection – Was there an attack?

  3. Host Based Methods • Virus Scanners • File System Integrity Checkers (Tripwire, DERBI) • Audit Logs • System Call Monitoring – Self/Nonself (Forrest)

  4. Network Based Methods • Firewalls • Signature Detection (SNORT, Bro) • Anomaly Detection (eBayes, NIDES, ADAM, SPADE)

  5. User Modeling • Source address – unauthorized users of authenticated services (telnet, ssh, pop3, imap) • Destination address – IP scans • Destination port – port scans

  6. Frequency Based Models • Used by SPADE, ADAM, NIDES, eBayes, etc. • Anomaly score = 1/P(event) • Event probabilities estimated by counting

  7. Attacks on Public Services PHF – exploits a CGI script bug on older Apache web servers GET /cgi-bin/phf?Qalias=x%0a/usr /bin/ypcat%20passwd

  8. Buffer Overflows • 1988 Morris Worm – fingerd • 2003 SQL Sapphire Worm char buf[100]; gets(buf); buf Exploit code stack 0 100 Return Address

  9. TCP/IP Denial of Service Attacks • Teardrop – overlapping IP fragments • Ping of Death – IP fragments reassemble to > 64K • Dosnuke – urgent data in NetBIOS packet • Land – identical source and destination addresses

  10. Protocol Modeling • Attacks exploit bugs • Bugs are most common in the least tested code • Most testing occurs after delivery • Therefore unusual data is more likely to be hostile

  11. Protocol Models • PHAD, NETAD – Packet Headers (Ethernet, IP, TCP, UDP, ICMP) • ALAD, LERAD – Client TCP application payloads (HTTP, SMTP, FTP, …)

  12. Time Based Models • Training and test phases • Values never seen in training are suspicious • Score = t/p = tn/r where • t = time since last anomaly • n = number of training examples • r = number of allowed values • p = r/n = fraction of values that are novel

  13. Example tn/r • Training: 0000111000 n/r = 10/2 • Testing: 01223 • 0: no score • 1: no score • 2: tn/r = 6 x 10/2 = 30 • 2: tn/r = 1 x 10/2 = 5 • 3: tn/r = 1 x 10/2 = 5

  14. PHAD – Fixed Rules • 34 packet header fields • Ethernet (address, protocol) • IP (TOS, TTL, fragmentation, addresses) • TCP (options, flags, port numbers) • UDP (port numbers, checksum) • ICMP (type, code, checksum) • Global model

  15. LERAD – Learns conditional Rules • Models inbound client TCP (addresses, ports, flags, 8 words in payload) • Learns conditional rules If port = 80 then word1 = GET, POST (n/r = 10000/2)

  16. LERAD Rule Learning • If word1 = GET then port = 80 (n/r = 2/1) • word1 = GET, HELO (n/r = 3/2) • If address = Marx then port = 80, 25 (n/r = 2/2)

  17. LERAD Rule Learning • Randomly pick rules based on matching attributes • Select nonoverlapping rules with high n/r on a sample • Train on full training set (new n/r) • Discard rules that discover novel values in last 10% of training (known false alarms)

  18. DARPA/Lincoln Labs Evaluation • 1 week of attack-free training data • 2 weeks with 201 attacks Internet Router Sniffer Attacks SunOS Solaris Linux NT

  19. Attacks out of 201 Detected at 10 False Alarms per Day

  20. Problems with Synthetic Traffic • Attributes are too predictable: TTL, TOS, TCP options, TCP window size, HTTP, SMTP command formatting • Too few sources: Client addresses, HTTP user agents, ssh versions • Too “clean”: no checksum errors, fragmentation, garbage data in reserved fields, malformed commands

  21. Real Traffic is Less Predictable Real r (Number of values) Synthetic Time

  22. Mixed Traffic: Fewer Detections, but More are Legitimate

  23. Project Status • Philip K. Chan – Project Leader • Gaurav Tandon – Applying LERAD to system call arguments • Rachna Vargiya – Application payload tokenization • Mohammad Arshad – Network traffic outlier analysis by clustering

  24. Further Reading • Learning Nonstationary Models of Normal Network Traffic for Detecting Novel Attacks by Matthew V. Mahoney and Philip K. Chan, Proc. KDD. • Network Traffic Anomaly Detection Based on Packet Bytes by Matthew V. Mahoney, Proc. ACM-SAC. • http://cs.fit.edu/~mmahoney/dist/

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