Automatic Static Unpacking of Malware Binaries
Department of Computer Science
University of Arizona
Tucson, AZ 85721, U.S.A.
Current malware is often transmitted in packed or encrypted form to prevent examination by anti-virus software. To analyze new malware, researchers typically resort to dynamic code analysis techniques to unpack the code for examination. Unfortunately, these dynamic techniques are susceptible to a variety of anti-monitoring defenses, as well as "time bombs" or "logic bombs," and can be slow and tedious to identify and disable. This paper discusses an alternative approach that relies on static analysis techniques to automate this process. Alias analysis can be used to identify the existence of unpacking, static slicing can identify the unpacking code, and control flow analysis can be used to identify and neutralize dynamic defenses. The identified unpacking code can be instrumented and transformed, then executed to perform the unpacking. We present a working prototype that can handle a variety of malware binaries, packed with both custom and commercial packers, and containing several examples of dynamic defenses.