🛡️Advanced⏱ 120 min

Smart Contract Security on Base

Security is the most critical skill for any Solidity developer. This quest covers the top vulnerability classes: reentrancy, integer overflow, access control, oracle manipulation, flash loan attacks, and more. Each challenge has a vulnerable contract you must exploit, then patch.

securitysolidityreentrancyauditethernaut

Prerequisites:Token Launch & Flywheel Mastery

🏆

Ability to audit Solidity contracts and prevent common attack vectors

Step 1: Reentrancy — exploit and fix

The classic reentrancy attack drains a contract by re-entering before balances are updated. Exploit the vulnerable contract, then apply the checks-effects-interactions pattern to fix it.

Step 1 — solidity

// Vulnerable contract
contract VulnerableBank {
    mapping(address => uint) public balances;

    function withdraw() external {
        uint amount = balances[msg.sender];
        (bool success,) = msg.sender.call{value: amount}('');
        require(success);
        balances[msg.sender] = 0; // ❌ Updated AFTER external call
    }
}

// Fixed contract
contract SafeBank {
    mapping(address => uint) public balances;

    function withdraw() external {
        uint amount = balances[msg.sender];
        balances[msg.sender] = 0;          // ✅ Update BEFORE external call
        (bool success,) = msg.sender.call{value: amount}('');
        require(success);
    }
}

✓

Checkpoint

Reentrancy attack proof-of-concept deployed and exploit transaction confirmed

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