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A Network Security Monitor

A Network Security Monitor. Paper By: Heberlein et. al. Presentation By: Eric Hawkins. Paper Background. Authors (Heberlein, Dias, Levitt, Mukherjee, Wood, and Wolber) all from CSC at UC Davis One of the leading research institutions for security Published in 1990

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A Network Security Monitor

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  1. A Network Security Monitor Paper By: Heberlein et. al. Presentation By: Eric Hawkins

  2. Paper Background • Authors (Heberlein, Dias, Levitt, Mukherjee, Wood, and Wolber) all from CSC at UC Davis • One of the leading research institutions for security • Published in 1990 • One of the seminal papers in intrusion detection / network security

  3. The Problem • How to keep computer networks secure against network attacks and intrustions? • Computer systems and networks were designed around trusted users • Cannot simply close off the network – need interconnection with “outside world” • Encryption, private keys, etc. cannot protect against all threats • e.g. legitimate users misusing privileges

  4. The Idea • A network security monitor that compares current network activity to historical behavior in order to detect usage anomalies • Capture network traffic • Analyze traffic based on historical activity patterns and/or pre-defined rules

  5. Discussion of Attacks • Preparation Phase • More prepared attackers are more difficult to defend against • Attack Phase • Target offers service that Attacker exploits • Target seeks to use service offered by Attacker • Post-Attack Phase

  6. Concept of the N.S.M. • 4-D matrix, axes are: • Source • Destination • Service • Connection ID • Each cell in matrix represents a unique connection • Each cell contains: • Number of packets passed on the connection • Cumulative sum of the data carried by those packets

  7. Concept of the N.S.M. (2) • The traffic matrix can be compared against particular patterns to match types of attacks • Patterns must be generated for such attacks • Use probability distributions to determine which measurements are likely to indicate attacks • Rules can also be employed to develop patterns • e.g. rule looking for a login connection that only exchanges a few packets and terminates • Difficult to apply hierarchically

  8. N.S.M. Architecture • Packet catcher – captures all packets • Parser – extracts protocol info (addressing, service, etc.) • Matrix Generator – creates cells or increments counts in 4-D matrix constructed of linked-lists • Matrix Analyzer – examines matrix representing current traffic against “normal traffic” (masking) or by applying rules • Matrix Archiver – saves traffic matrix

  9. Results • Identified problems which were actually just abuse of network privileges • Full backups using FTP • Programs continually executing finger • Thrown off when a network file server went down • Detected several consecutive failed log-ins

  10. Difficulties • How do you train the monitor for a “normal” usage pattern? Who’s to say a security breach isn’t occurring while training? • Defining rules for non-trivial attacks will be difficult • Network traffic is not accessible when networks use non-broadcast media (think: switches vs. hubs)

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