If you want to find vulnerabilities in software, fuzzing is one of your best friends.
The idea is simple: you throw a massive amount of unexpected, malformed, or just plain weird input at an application and watch what breaks. No source code required. No reversing needed (at least not at first). Just you, your fuzzer, and whatever the target throws back at you.
This is the FTP fuzzer I built back when I was going deep down the rabbit hole of exploit development and vulnerability research. It targets FTP servers specifically — but because FTP is a plain-text TCP protocol, the approach translates pretty easily to other protocols in the same family. If you understand how this works, you can adapt it.
Why FTP?
FTP is one of those protocols that’s been around forever, which means there’s a lot of software out there that implements it — and not all of it has been thoroughly tested. Old implementations, niche server software, embedded devices. There’s still life in this space if you know where to look.
What this tool has actually done
This isn’t a toy. This fuzzer has been used to discover a number of previously undisclosed bugs in real FTP server software. Finding a bug that nobody’s publicly documented yet is a genuinely satisfying feeling — and it’s how you start building a reputation in this industry.
Where to get it
The project is open source and hosted on GitHub:
https://github.com/nullsecuritynet/tools/blob/main/fuzzer/ftp-fuzz/release/ftp-fuzz.py
Pull it down, read through it, and — more importantly — actually run it against a test environment. Don’t just copy-paste commands and move on. Understand what it’s sending and why. That’s the bit that actually makes you better.
If you’re getting into vulnerability research or exploit development, fuzzing is a skill you want in your toolkit early. Start here.