Smart Contract Vulnerabilities: 7 Security Mistakes That Keep Draining Millions in Web3

Every few months, there is another headline. A protocol gets exploited. Liquidity disappears. Users panic. Founders post apology threads. After a while, it stops feeling shocking. What makes it frustrating is that most of these exploits are not the result of impossible mathematics or some mysterious cryptographic breakthrough. They are usually ordinary development mistakes. The kind that happens when teams move quickly, reuse code, or assume something is safe because it worked somewhere else. Blockchain technology itself is not fragile. Smart contracts are deterministic. The weakness almost always comes from human decisions. Let us walk through seven common mistakes that continue to cost Web3 millions. 1. Reentrancy still shows up Reentrancy is not new. The exploit on The DAO made that painfully clear years ago. Yet it still appears in audits today. The issue is simple in theory. A contract sends funds to an external address before updating its internal state. If that external address