Abstract Fizzer is a new gray-box fuzzer. In contrast to common gray-box fuzzers that aim to cover both and branches of branching instructions, Fizzer primarily aims to cover both possible values and of Boolean expressions in the program. When a generated test evaluates a so-called atomic Boolean expression to one of these values, our fuzzer computes the distance to the other value, detects bytes that influence this distance, and applies gradient descent on these bytes to flip the value. In Test-Comp 2024, Fizzer placed third in the category Cover-Branches after FuSeBMC and FuSeBMC-AI.

Abstract We present a gray-box fuzzing approach based on several new ideas. While standard gray-box fuzzing aims to cover all branches of the input program, our approach primarily aims to cover both results of each Boolean expression. To achieve this goal, we track the distances to flipping these results and we dynamically detect the input bytes that influence the distance. Then we use this information to efficiently flip the results. More precisely, we apply gradient descent on the detected bytes or we create new inputs by using detected bytes from different inputs. We implemented our approach in a tool called Fizzer. An evaluation on the benchmarks of Test-Comp 2023 shows that Fizzer is fully competitive with the winning tools of the competition, which use advanced formal methods like symbolic execution or bounded model checking, usually in combination with fuzzing.