Chapter 14: Fuzzing Techniques

What is fuzzing? You’ve already done some fuzzing as part of our exercises elsewhere in this book. When we were exploring our vulnerable C programs, we would fire up the GNU Debugger and watch the state of the registers as we threw more and more data at the user prompt. We were modifying our input with each iteration and trying to cause a crash or at least some anomalous behavior. The inputs to the program can be malformed in some sense – an invalid format, adding unexpected or invalid characters, or simply providing too much data. The fuzzing target doesn’t even have to be a program – it could be a network service implementing some particular protocol, or even the encoder that generates a file in a particular format, such as a PDF or JPG. If you’ve ever worked in software development, then the idea should be immediately familiar. Fuzzing can find flaws that could negatively impact the user experience, but...