Welcome to fuzz week 2020! This week (July 13th - July 17th) I’ll be streaming every day going through some of the very basics of fuzzing all the way to cutting edge research. I want to use this time to talk about some things related to fuzzing, particularly when it comes to benchmarking and comparing fuzzers with each other.


Ha. There’s really no schedule, there is no script, there is no plan, but here’s a rough outline of what I want to cover.

I will be streaming on my Twitch channel at approximately 14:00 PST. But things aren’t really going to be on a strict schedule.

My Twitter is probably the best source of information for when things are about to start.

Everything will be recorded and uploaded to my YouTube.

July 13th

The very basics of fuzzing. We’ll write our own fuzzer and tweak it to improve it. We’ll probably start by writing it in Python, and eventually talk about the performance ramifications and the basics of scaling fuzzers by using threads or multiple processes. We’ll also compare our newly written fuzzer against AFL and see where AFL outperforms it, and also where AFL has some blind spots.

July 14th

Here we’ll cover code coverage. We might get to this sooner, who knows. But we’re going to write our own tooling to gather code coverage information such that we can see not only how easy it is to set up, but how flexible coverage information can be while still proving quite useful!

July 15th-17th

Here we’ll focus mainly on the advanced aspects of fuzzing. While this sounds complex, fuzzing really hasn’t become that complex yet, so follow along! We’ll go through some of the more deep performance properties of fuzzing, mainly focused around snapshot fuzzing.

Once we’ve discussed some basics of performance and snapshot fuzzing, we’ll start talking about the meaningfulness of comparing fuzzers. Namely, the difficulties in comparing fuzzers when they may involve different concepts of what a crash, coverage, or input are. We’ll look at some existing examples of papers which compare fuzzers, and see how well they actually prove their point.


I think it’s important when doing something like this, to make it clear what my existing biases are. I’ve got a few.

  • I think existing fuzzers have some major performance problems and struggle to scale. I consider this to be a high priority as general performance improvements to fuzzing harnesses makes both generic fuzzers (eg. AFL, context-unaware fuzzers) and hand-crafted (targeted) fuzzers better.
  • I don’t think outperforming AFL is impressive. AFL is impressive because it’s got an easy-to-use workflow, which makes it accessible to many different users, broadening the amount of targets it has been used against.
  • I don’t really thinking comparing fuzzers is reasonable.
  • I think it is very easy to over-fit a fuzzer to small programs, or add unrealistic amounts of information extraction from a target under test, in a way that the concepts are not generally applicable to many targets that exceed basic parsers. I think this is where a lot of current research falls.

But… that’s mainly the point of this week. To either find out my biases are wildly incorrect, or to maybe demonstrate why I have some of the biases. So, how will I address some of these (in order of prior bullets)?

  • I’ll compare some of my fuzzers against AFL. We’ll see if we can outperform AFL in terms of raw fuzz cases performed, as well as the results (coverage and crashes).
  • I’ll try to demonstrate that a basic fuzzer with 1/100th the amount of code of AFL is capable of getting much better results, and that it’s really not that hard to write.
  • I’ll propose some techniques that can be used to compare fuzzers, and go through my own personal process of evaluating fuzzers. I’m not trying to get papers, or funding, or anything. I don’t really have an interest in making things look comparatively better. If they perform differently, but have different use cases, I’d rather understand those cases and apply them specifically rather than have a one-shoe-fits-all solution.
  • I’ll go through some instrumentation that I’ve historically added to my fuzzers which give them massive result and coverage boosts, but consume so much information that they cannot meaningfully scale past tiny pieces of code. I’ll go through when these things may actually be useful, as sometimes isolating components is viable. I’ll also go through some existing papers and see what sorts of results are being claimed, and if they actually have general applicability.

Winging it

It’s important to note, nothing here is scheduled. Things may go much faster, slower, or just never happen. That’s the beauty of research. I may be very wrong with some of my biases, and we’ll hopefully correct those. I love being wrong.

I’ve maybe thought of having some fuzzing figureheads pop on the stream for random discussions/conversations/interviews. If this is something that sounds interesting to you, reach out and we can maybe organize it!

Sound fun?

See you there :)