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Nexus Intelligence Research
Nexus Intelligence Research

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DeFi Smart Contract Vulnerabilities Audit Guide

Here are three critical DeFi smart contract vulnerabilities, described with the level of specificity required for a professional security audit report. Each entry includes the vulnerability classification, root cause, impact analysis, and a recommended mitigation strategy.

1. Reentrancy via External Call Before State Update

Vulnerability Class: Reentrancy (CWE-841)

Severity: Critical

Affected Function: withdraw(uint256 _amount) in a staking or lending protocol.

Description:

The withdraw function performs an external call to a user-controlled IERC20 token contract (token.transfer(msg.sender, _amount)) before updating the internal accounting state (userBalances[msg.sender] -= _amount). If the token is a malicious or non-standard ERC-20 implementation, it can re-enter the withdraw function during the execution of transfer by calling back into the protocol. Since the balance has not

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