On the Effectiveness of Synthetic Benchmarks for Evaluating Directed Grey-Box Fuzzers

Directed grey-box fuzzing is difficult to rigorously evaluate for several reasons. First, directed grey-box fuzzers are more prone to overfitting than undirected grey-box fuzzers as they are designed to explore specific paths in the program under test. Furthermore, existing benchmarks are mainly designed for evaluating undirected fuzzers. Hence, they do not provide any information about bug locations, and the difficulty of triggering bugs can substantially vary across different benchmarks. In this paper, we argue that one can address these challenges by automatically generating benchmarks with a bug synthesis technique. Notably, Fuzzle, a state-of-the-art bug synthesis tool, enables generation of arbitrarily many benchmarks, thereby preventing the overfitting problem. It is also well suited for evaluating directed grey-box fuzzers as it provides the exact location of the target bug in the generated benchmark with a guarantee that the bug is lurking deep in the program. With Fuzzle, we systematically evaluate existing state-of-the-art directed fuzzers and study their strengths and weaknesses, which would be otherwise difficult to obtain with traditional benchmarks. To our knowledge, this is the first attempt to adopt a bug synthesis technique for evaluating directed fuzzers.