How Reentrancy Attacks Work in Solidity — and How to Prevent Them

How Reentrancy Attacks Work in Solidity — and How to Prevent Them Why I'm Writing This I've seen reentrancy bugs in production code exactly twice. Both times, the developer knew about it in theory but brushed it off as "unlikely." One cost a company $40k in lost funds before we patched it. The other was caught in audit, thank God. The frustrating part? These aren't subtle bugs hidden in complex math. They're straightforward to understand and straightforward to prevent. You just have to actually do it. Reentrancy isn't going away. It's one of the oldest classes of vulnerabilities in Ethereum (remember the DAO hack in 2016?), and I still see it in production contracts. So here's how it works, where it bites you, and the fixes that actually work. What Is Reentrancy? Reentrancy happens when a function calls another contract before it finishes updating its own state. That external contract can then call back into the original function before state is settled. Think of it like a recursive lo