DeFi Smart Contract Vulnerabilities Audit Guide

Here are three specific DeFi smart contract vulnerabilities suitable for inclusion in a security audit report. Each entry includes the vulnerability class, a realistic code scenario, the exploit mechanism, and recommended mitigations.

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1. Reentrancy Attack in Token Transfer Callbacks

Vulnerability Class: Reentrancy (CWE-841)

Severity: Critical

Affected Pattern: Unprotected external calls during state changes (e.g., token distribution, claim functions).

Description

A reentrancy vulnerability occurs when a smart contract makes an external call to an untrusted address before updating its internal state. If the called contract is malicious, it can re-enter the vulnerable function before the state is updated, leading to repeated executions and draining of funds.

Code Example (Vulnerable)

solidity
// PullPayment.sol
function withdraw() public {
    uint256 amount = payment[user];
    require(amount >