Show HN: PyFuzz2 – A little fuzzing framework in Python

Fuzz testing is often used for things like compilers, and involves feeding random input into it attempting to find bugs. It is useful for finding complex behavior and race conditions and stuff.

https://en.wikipedia.org/wiki/Fuzz_testing

Well, you sort of hit the nail on the head, but with a few more advanced techniques to amp the process up.

Essentially, a fuzzer is a vulnerability finding tool that automates the process of injecting randomized values into input fields, and then tracking what breaks. Different modules can create different types of input that are likely to cause certain types of faults. Peruse the documentation of one of the established fuzzers to see it in action (see my other comment.)

Pretty much it. You often provide them with a corpus and they start mutating it and trying lots of random data based on it with the goal being to crash code. Fuzzing actually catches a remarkable number of problems with code.

The one I've seen the most of recently in general, and probably the highest quality blogs about it, has been American Fuzzy Loop, AFL: http://lcamtuf.coredump.cx/afl/ there are a number of programs in its treasure chest, I'd encourage looking at a few of the links if you're even remotely curious about the bugs fuzzing can expose.

This one has been making a fair splash in the go community, take a look at the trophy list about a third of the way down the page: https://github.com/dvyukov/go-fuzz

Not just networked things, you can fuzz anything that takes input, eg a function. Imagine it as 10000 rabid monkeys writing testcases for you.

Instead of pure random data, fuzzers can use 'attack heuristics' to try and minimize the search space. These are specific patterns that are more likely to expose bugs, based on previous vulnerabilities and known coding errors. For example using '%n%n%n%n%n' many times to exploit C-style format string stack vulnerabilities.

Mozilla started a project known as FuzzDB to collect these heuristics, although it doesn't appear to have been maintained recently.

Here's some examples from FuzzDB: https://code.google.com/p/fuzzdb/source/browse/trunk/attack-...

I prefer Hypothesis. It's not so much a fuzzer as a library to generate data for unit tests, and thus fits much more easily in the development flow.