Automatic Test Data Generation in File Format Fuzzers

Fuzzing is a dynamic software testing technique. In this technique with repeated generation and injection of malformed test data to the software under test (SUT), we are looking for the possible errors and vulnerabilities. Files are significant inputs to most real-world applications. Many of test data which are generated for fuzzing such programs are rejected by the parser because they are not in the acceptable format and this results in a low code coverage in the process of fuzz testing. Using the grammatical structure of input files to generate test data leads to increase code coverage. However, often, the grammar extraction is performed manually, which is a time consuming, costly and error-prone task. In this paper, a new method, based on deep neural language models (NLMs), is proposed for automatically learning the file structure and then generating and fuzzing test data. Our experiments demonstrate that the data produced by this method leads to an increase in the code coverage compared to previous test data generation methods. For MuPDF software, which accepts the PDF complex file format as an input, we have more than 1.30 to 12 percent improvement in code coverage than both the intelligence and random methods.