1

I have an IoT system that has a command-line-based interactive shell that can be used to configure the system. While examining the disassembly/decompilation, I realized that there is a lot of functionality/code to the CLI and a lot of possible logical paths in the program. As such, I have not outright identified any memory corruption vulnerabilities, but I suspect that there may be edge cases that could result in a bug. This is where I would normally apply fuzzing to bolster my coverage.

However, I am having trouble identifying an approach to creating a suitable input corpus to fuzz with. The CLI supports a number of commands, and some of them even spawn their own interactive CLI with many levels of namespaces. It may take several commands to reach certain parts of the program.

I have two thoughts on how to go about this:

  1. Create a comprehensive corpus, including a large number of commands and possible paths. Will be tedious to construct; impossible to cover everything.
  2. No input corpus; use entirely feedback-driven fuzzing (if even possible in this case). Seems like this would be very inefficient, as there would be many paths for the fuzzer to learn.

I am able to run the binary through the fuzzer and I believe the fuzzer is passing input to it correctly, so that's not an issue. I was planning on using honggfuzz for this, but I don't think that really matters for the question. I don't have source code, so this will be black box and un-instrumented fuzzing.

My question is, how should I approach creating an input corpus to fuzz a black-box program that has many possible inputs?

1

1 Answer 1

1

Thanks to @julian's comment, I was able to search for more relevant terms.

For this particular case, I decided to use AFL's dictionary mode, where you can give it a list of words that make up the target application's accepted syntax.

For example, let's pretend the target application is an interactive calculator, which supports all basic mathmatical operators, e.g. 4 + 5 or 500 / 2. For this, I would create a dictionary file with the following contents:

"+"
"-"
"*"
"/"
"^"
...

In addition to a typical set of input cases, this file (or a directory of files with one valid piece of syntax each) would be passed to AFL with the -x option, and AFL will try to create valid syntax to improve fuzzing coverage.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.