"Why 6?" Defining the Operational Limits of Stide, an Anomaly-Based Intrusion Detector

  • Authors:
  • Kymie M. C. Tan;Roy A. Maxion

  • Affiliations:
  • -;-

  • Venue:
  • SP '02 Proceedings of the 2002 IEEE Symposium on Security and Privacy
  • Year:
  • 2002

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Abstract

Anomaly-detection techniques have considerable promise for twodifficult and critical problems in information security and intrusiondetection: detecting novel attacks, and detecting masqueraders.Oneof the best-known anomaly detectors used in intrusion detection isstide.Developed at the University of New Mexico, stide aims todetect attacks that exploit processes that run with root privileges.The original work on stide presented empirical results indicatingthat data sequences of length six and above were required foreffective intrusion detection.This observation has given rise tothe long-standing question, "Why six?" accompanied by relatedquestions regarding the conditions under which six may or may not beappropriate.This paper addresses the "Why Six" issue by presenting anevaluation framework that maps out stide's effective operating space,and identifies the conditions that contribute to detectioncapability, particularly detection blindness.A theoreticaljustification explains the effectiveness of sequence lengths of sixand above, as well as the consequences of using other values.Inaddition, results of an investigation are presented, comparingstide's anomaly-detection capabilities with those of a competingdetector.