DeFi Smart Contract Vulnerabilities Audit Guide

Here are three of the most common and critical DeFi smart contract vulnerabilities, along with specific methods to detect them during code review or audits.

1. Reentrancy Attacks

Description:
Reentrancy occurs when an external contract call is made before the state of the current contract is updated. A malicious contract can re-enter the vulnerable function before the state change is complete, allowing an attacker to drain funds by repeatedly calling the function before the balance is reduced.

Specific Detection Methods:

• State-Change-After-External-Call Pattern: Look for functions that interact with external contracts (via call, delegatecall, or transfer) before updating the internal state (e.g., balances[msg.sender]).
  • Example of Bad Code:

solidity
      function withdraw(uint amount) public {
          require(balances[msg.sender] >= amount);
          (bool success, ) = msg