App developers are increasingly using packing services (or packers) to protect their code against being reverse engineered or modified. However, such packing techniques are also leveraged by the malicious developers to prevent the malware from being analyzed and detected by the static malware analysis and detection systems. Though there are already studies on unpacking packed Android apps, they usually leverage the manual reverse engineered packing behaviors to unpack apps packed by the specific packers and cannot be applied to the evolving and new packers. In this paper, we propose a novel unpacking approach with the capacity of adaptively unpacking the evolving and newly encountered packers. Also, we develop a new system, named PackerGrind, based on this adaptive approach for unpacking Android packers. The evaluation with real packed apps demonstrates that PackerGrind can successfully reveal packers? protection mechanisms, effectively handle their evolution and recover Dex files with low overhead.
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