DeFi Smart Contract Vulnerabilities Audit Guide

Here are three specific DeFi smart contract vulnerabilities commonly identified in professional audit reports, described with technical precision suitable for inclusion in a formal security assessment.

1. Reentrancy Vulnerability in External Calls

Description:

A reentrancy vulnerability occurs when a smart contract makes an external call to another contract (e.g., transferring tokens to a user) before updating its internal state variables. If the external contract is malicious, it can re-enter the original contract through the same function during the execution of the external call, potentially bypassing checks that rely on the outdated state.

Specific Example:

Consider a withdraw() function in a lending protocol:

solidity
function withdraw(uint256 amount) public {
    require(balances[msg.sender] >= amount, "Insufficient balance");

    // VULNERABILITY: External call before state update
    (bool success, ) = msg.sender.call{value: amount}("");