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Example of Anomaly Detection

Example of Anomaly Detection. Sequence of system calls (Forrest 1996) Training Training data: open read write open mmap write fchmod close Sliding window of size 1+3 (1 followed by 3) open read write open open mmap write fchmod read write open mmap write open mmap write

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Example of Anomaly Detection

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  1. Example of Anomaly Detection • Sequence of system calls (Forrest 1996) • Training • Training data: open read write open mmap write fchmod close • Sliding window of size 1+3 (1 followed by 3) open read write open open mmap write fchmod read write open mmap write open mmap write write fchmod close mmap write fchmod close fchmod close close • This is the normal behavior

  2. Example of Anomaly Detection • Detection open read write open open mmap write fchmod read write open mmap write open mmap write write fchmod close mmap write fchmod close fchmod close close • open read readopen mmap write fchmod close • Differs in 5 places: • Second read should be write (1st line) • Second read should be write (3rd line) • Second open should be write (3rd line) • mmap should be open (3rd line) • write should be mmap (3rd line) • 18 possible places of difference • 18=5*3+2+1 • Mismatch rate 5/18  28% ? A pre-defined threshold

  3. Stack Frame c o d e r e t a d d r r e t a d d r 3 GB w/o Randomization b u f Exploit!

  4. Stack Frame c o d e r e t a d d r r e t a d d r 3 GB w/ Randomization b u f b u f crash

  5. Stack Frame c o d e r e t a d d r r e t a d d r De-Randomization 1 Pad b u f crash Step 1

  6. Stack Frame c o d e r e t a d d r r e t a d d r De-Randomization 2 Pad b u f crash Step 2

  7. Stack Frame c o d e r e t a d d r r e t a d d r De-Randomization 3 Pad b u f Exploit! 216 seconds (avg.) to de-randomize! Step 3 http://www.stanford.edu/~blp/papers/asrandom.pdf

  8. c o d e Spraying Attacks • Exploit a buggy application and “spray” attack code in write-able user-level memory areas b u f Exploit!

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