defi-amm-security

DeFi AMM Security

Critical vulnerability patterns and hardened implementations for Solidity AMM contracts, LP vaults, and swap functions.

When to Use

• Writing or auditing a Solidity AMM or liquidity-pool contract
• Implementing swap, deposit, withdraw, mint, or burn flows that hold token balances
• Reviewing any contract that uses token.balanceOf(address(this)) in share or reserve math
• Adding fee setters, pausers, oracle updates, or other admin functions to a DeFi protocol

How It Works

Use this as a checklist-plus-pattern library. Review every user entrypoint against the categories below and prefer the hardened examples over hand-rolled variants.

Examples

Reentrancy: enforce CEI order

Vulnerable:

function withdraw(uint256 amount) external {
    require(balances[msg.sender] >= amount);
    token.transfer(msg.sender, amount);
    balances[msg.sender] -= amount;
}

Safe:

import {ReentrancyGuard} from "@openzeppelin/contracts/utils/ReentrancyGuard.sol";
import {SafeERC20} from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

using SafeERC20 for IERC20;

function withdraw(uint256 amount) external nonReentrant {
    require(balances[msg.sender] >= amount, "Insufficient");
    balances[msg.sender] -= amount;
    token.safeTransfer(msg.sender, amount);
}

Do not write your own guard when a hardened library exists.

Donation or inflation attacks

Using token.balanceOf(address(this)) directly for share math lets attackers manipulate the denominator by sending tokens to the contract outside the intended path.

// Vulnerable
function deposit(uint256 assets) external returns (uint256 shares) {
    shares = (assets * totalShares) / token.balanceOf(address(this));
}

// Safe
uint256 private _totalAssets;

function deposit(uint256 assets) external nonReentrant returns (uint256 shares) {
    uint256 balBefore = token.balanceOf(address(this));
    token.safeTransferFrom(msg.sender, address(this), assets);
    uint256 received = token.balanceOf(address(this)) - balBefore;

    shares = totalShares == 0 ? received : (received * totalShares) / _totalAssets;
    _totalAssets += received;
    totalShares += shares;
}