challenge-22-Dex

Ethernaut Challenge 21

In this challenge the user is provided with a contract called Dex.sol. The goal of this challenge is to drain token0.

Solution

1. The problem in this contract is the way the contract quotes token prices. Initially the user is given 10 token0 & 10 token1. The dex already has 100 token0 & 100 token1. The initial price is 1 token0 = 1 token1.

2. Swapping 10 token0 for token1 gives us 20 token1 & 0 token0. But the dex now has 110 token0 & 90 token1. The next quote price if we swap 20 token1 for token0 it gives us 24 token0 which is better than before.

3. Swapping tokens back & forth a few more times gives us better & better price & we drain all of the funds in the dex.

4. Run Exploit!

forge test -vv -m test_challenge_21