DeFi Smart Contract Vulnerabilities Audit Guide

Here are three specific DeFi smart contract vulnerabilities commonly identified in professional audit reports, complete with technical context, root causes, and remediation strategies.

1. Reentrancy via Callbacks in Cross-Protocol Interactions

Vulnerability Class: Reentrancy (CWE-841)

Severity: High/Critical

Common Context: Yield Aggregators, Vaults, and Multi-Step Swaps

Description

While classic reentrancy (e.g., in ERC-20 balances) is often mitigated by using nonReentrant modifiers or checks-effects-interactions (CEI) patterns, cross-protocol reentrancy remains a prevalent risk. This occurs when a contract calls an external protocol (e.g., a lending market or AMM) that allows user-supplied callbacks or custom logic during the transaction.

Specific Scenario

A vault contract (Vault.sol) performs a two-step operation:
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