The minefield between syntaxes: exploiting syntax confusions in the wild

In this article, you will discover unique, advanced techniques for exploiting confusion across various programming languages arising from differing syntaxes, which I will refer to as ‘syntax confusion’.

I’ll provide step-by-step guidance, supported by with practical examples, on crafting payloads to confuse syntaxes and parsers – enabling filter bypasses and real-world exploitation.

Developers often assume there is only one valid syntax for a given input, without considering that identical data can be represented in different syntax variations with the same outcome. For instance, a file upload request can use multipart form data with a standard filename parameter, but the parameter can also be defined in extended syntax as filename*=UTF-8’’.

Whether you’re a pentester, security researcher or Bug Bounty hunter, this guide offers actionable advice on transforming theoretical payloads into effective techniques that uncover unexpected vulnerabilities.

You can also explore these methods by watching my presentation of this research at NahamCon 2025 (free signup required).

You can find the full article on YesWeHack’s blog page