✅ You Can Defend Against Reentrancy
Protect your contracts using CEI pattern and OpenZeppelin guards
Your Progress
0 / 5 completed←
Previous Section
Prevention Methods
🎓 Module Complete: Key Takeaways
🎉 Congratulations!
You've completed the Reentrancy Attack module. You now understand one of the most critical vulnerabilities in smart contract security and how to prevent it.
📚 What You've Learned
🎯
Reentrancy Fundamentals
- •Occurs when external calls happen before state updates
- •Attacker reenters with stale state, bypassing checks
- •Most dangerous vulnerability in smart contracts
📜
The DAO Hack
- •$60M stolen through splitDAO reentrancy
- •Led to Ethereum hard fork (ETH vs ETC)
- •Catalyzed modern security practices
🛡️
Prevention Methods
- •Use OpenZeppelin's ReentrancyGuard modifier
- •Follow Checks-Effects-Interactions pattern
- •Consider pull payment architecture
📋
Best Practices
- •Update state before external calls always
- •Audit every external call carefully
- •Test with reentrancy attack simulations
⚠️
Common Variations
- •Single-function: Same function repeatedly
- •Cross-function: Reenter different function
- •Delegatecall: Storage context exploitation
🔍
Security Mindset
- •Never trust external contracts
- •Assume all addresses are malicious
- •Defense in depth: use multiple protections
🎯 Interactive: Security Knowledge Quiz
Test your understanding with 5 questions about reentrancy attacks and prevention methods.
🛠️ Security Checklist for Your Projects
✅ Before Deployment
Add
nonReentrant to functions with external callsVerify Checks-Effects-Interactions pattern
Update all state before external calls
Test with reentrancy attack simulations
Run Slither/Mythril static analysis
🔍 During Review
Check cross-function reentrancy risks
Verify all external calls are documented
Confirm no delegatecall vulnerabilities
Review fallback/receive functions
Get professional security audit
📖 Recommended Resources
📘 OpenZeppelin Contracts
Battle-tested library with ReentrancyGuard and other security utilities.
npm install @openzeppelin/contracts🔍 Slither Static Analyzer
Automated tool that detects reentrancy and other vulnerabilities.
pip install slither-analyzer📚 ConsenSys Best Practices
Comprehensive smart contract security guidelines and patterns.
🎓 Ethernaut Challenges
Hands-on security challenges including reentrancy exploits.
🚀 Next Steps
1️⃣
Practice writing secure contracts: Build projects using OpenZeppelin's ReentrancyGuard and Checks-Effects-Interactions pattern.
2️⃣
Study real exploits: Analyze public post-mortems from hacks like The DAO, Cream Finance, and others.
3️⃣
Learn other vulnerabilities: Explore integer overflow, front-running, access control, and more security topics.
4️⃣
Contribute to security: Join bug bounty programs, audit open-source projects, share knowledge.
🎓
Module Mastered!
You now have the knowledge to identify, prevent, and defend against reentrancy attacks. Use this expertise to build secure, trustworthy smart contracts.
"Security is not a product, but a process." — Bruce Schneier