Stealing Malware Classifiers and AVs at Low False Positive Conditions
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Model stealing attacks have been successfully used in many machine learning domains, but there is little understanding of how these attacks work in the malware detection domain. Malware detection and, in general, security domains have very strong requirements of low false positive rates (FPR). However, these requirements are not the primary focus of the existing model stealing literature. Stealing attacks create surrogate models that perform similarly to a target model using a limited amount of queries to the target. The first stage of this study is the evaluation of active learning model stealing attacks against publicly available stand-alone machine learning malware classifiers and antivirus products (AVs). We propose a new neural network architecture for surrogate models that outperforms the existing state of the art on low FPR conditions. The surrogates were evaluated on their agreement with the targeted models. Good surrogates of the stand-alone classifiers were created with up to 99 training dataset size. Good AV surrogates were also possible to train, but with a lower agreement. The second stage used the best surrogates as well as the target models to generate adversarial malware using the MAB framework to test stand-alone models and AVs (offline and online). Results showed that surrogate models could generate adversarial samples that evade the targets but are less successful than the targets themselves. Using surrogates, however, is a necessity for attackers, given that attacks against AVs are extremely time-consuming and easily detected when the AVs are connected to the internet.
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