Welcome to this CTF challenge. I wrote a pretty efficient but simple on-chain order-book DEX using Huff. If you're not familiar with Huff, Huff is a low-level EVM language whereby instructions are written in the "word" mnemonic form, you can find the full list here. Huff adds some syntatic sugar like jump-labels and macros to improve the devs experience.

Disclaimer: This code has an explicitly added vulnerability, do not use in production!

To solve this CTF you must steal the tokens from the DEX. To do this go to ./test/HackHere.t.sol and add your exploit logic to the _executeSolution method. You'll know you've solved the challenge if the testSolve test passes. The vulnerable Huff contract is src/Challenge.huff. You may deploy and operate your own contracts but do not use any cheatcodes!

1. Install the Huff compiler using curl -L get.huff.sh | bash
2. Clone this repo using git clone [email protected]:Philogy/jessys-sussy-huff.git
3. Pull the dependencies using git submodule update --init --recursive
4. Run your exploit using forge test -vvv --ffi --match-path test/HackHere.t.sol

The DEX allows people to create orders trading ETH for MOCK tokens. Orders are created with addTo{Eth/Token}Order. Orders are matched using the matchEthOrder function whereby the buyer, seller and the price has to be passed in. The party who receives ETH needs to have sufficient tokens deposited to fill the order otherwise the function will revert.

Note: The stack comments are correct and not meant to trick you.