Reentrancy Attack Mechanisms

Reentrancy attacks occur when a function makes an external call to an untrusted contract before it updates its own internal state. The malicious contract can then recursively call back into the original function, repeatedly withdrawing funds before the balance is updated to zero.

This exploit effectively tricks the contract into releasing more assets than the user is entitled to. Developers prevent this by using reentrancy guards or by following the checks-effects-interactions pattern, which ensures all state changes occur before any external calls.

These attacks have been responsible for some of the largest losses in DeFi history. Understanding this mechanism is fundamental to secure smart contract development and rigorous auditing.