Gray-Box Fuzzing in Local Space

We consider gray-box fuzzing of a program instrumented such that information about evaluation of program expressions converting values of numerical types to Boolean, like x <= y, is recorded during each program's execution. Given that information for an executed program path, we formally define the problem for finding input such that program's execution with that input evaluates all those expressions in the same order and with the same Boolean values as in the original execution path, except for the last one, which is evaluated to the opposite value. Then we also provide an algorithm searching for a solution of the problem effectively. The effectiveness of the algorithm is demonstrated empirically via its evaluation on the TestComp 2024 benchmark suite.