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DeFi Smart Contract Vulnerabilities Audit Guide

Here are three specific DeFi smart contract vulnerabilities commonly identified in professional audit reports, including their mechanisms, impact, and prevention strategies.


1. Reentrancy Attack via Unprotected External Calls

Vulnerability Type: Reentrancy (CWE-369)

Severity: Critical

Affected Pattern: Token swaps, staking withdrawals, or any function that sends ETH/tokens before updating internal state.

Description

A reentrancy attack occurs when a smart contract makes an external call to an untrusted or semi-trusted contract before completing its state changes. The external contract can then re-enter the vulnerable function before the first invocation has finished, allowing an attacker to drain funds or manipulate state multiple times.

Specific Example


solidity
// VULNERABLE CODE
function withdraw() public {
    uint256 amount = balances[msg.sender];
    require(amount > 0, "No balance
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