solidity-securitylisted

# Solidity Security Master smart contract security best practices, vulnerability prevention, and secure Solidity development patterns. ## When to Use This Skill - Writing secure smart contracts - Auditing existing contracts for vulnerabilities - Implementing secure DeFi protocols - Preventing reentrancy, overflow, and access control issues - Optimizing gas usage while maintaining security - Preparing contracts for professional audits - Understanding common attack vectors ## Critical Vulnerabilities ### 1. Reentrancy Attacker calls back into your contract before state is updated. **Vulnerable Code:** ```solidity // VULNERABLE TO REENTRANCY contract VulnerableBank { mapping(address => uint256) public balances; function withdraw() public { uint256 amount = balances[msg.sender]; // DANGER: External call before state update (bool success, ) = msg.sender.call{value: amount}(""); require(success); balances[msg.sender] = 0; // Too late! } } ``` **Secure Pattern (Checks-Effects-Interactions):** ```solidity contract SecureBank { mapping(address => uint256) public balances; function withdraw() public { uint256 amount = balances[msg.sender]; require(amount > 0, "Insufficient balance"); // EFFECTS: Update state BEFORE external call balances[msg.sender] = 0; // INTERACTIONS: External call last (bool success, ) = msg.sender.call{value: amount}(""); require(suc