ZOZZLE:

Fast and Precise In-Browser JavaScript Malware Detection

W

HAT IS THE

P

ROBLEM

?

   JavaScript allows authors to run any code when a user visits a web page JS-based malware attacks are the majority of successful mass-scale exploitation Malware is easy to hide: self-generating code that produces more code to run    JS severs important functionality for many sites In-browser solutions have not been fully accepted because of the performance hit Browsers use offline scanning to check URLs but there are too many sites and malware typically comes and goes frequently

C

HALLENGES

    Performance  Detection is not fast enough to be used in a browser Accuracy  False positive rates of 5% is acceptable for static analysis tools but is over 100x what is acceptable for in-browser detection Obfuscated malware   Most JavaScript code is frequently obfuscated so purely static detection is generally ineffective Ex. eval , document.write

generate code at runtime that is difficult to pattern-match Malware transience   Offline-only scanning is not effective because web malware “infects fast and dies young” Nearly 20% of malicious URLs were gone after 1 day

S

OLUTION

: Z

OZZLE

 Performance   AST-based detection is fast and scalable Fast classification: throughput at over 1 MB of JavaScript code per second  Accuracy   AST-based detection uses hierarchical (context sensitive) features more precise than text-based Low false positive rate: 0.0003% (< 1 in 1/4 million)  De-obfuscation  Uses JavaScript engine of a browser to expose obfuscation and get the final, expanded version of JavaScript code

W

HAT

I

S

Z

OZZLE

?

  A highly precise, mostly static detector for malware written in JavaScript suitable for in browser deployment 3 Steps:    JavaScript context collection and labeling as benign or malicious Feature extraction and training of a naïve Bayesian classifier Applying the classifier to a new JavaScript context to determine if it is benign or malicious

Z

OZZLE

: H

OW

I

T

W

ORKS

  JavaScript runtime engine exposes attempts to obscure malware JS code is unfolded to just before it’s executed  Intercept calls to compile() engine in the JavaScript   It’s invoked when eval is called and whenever new code is included with an