Access Control

The mechanism by which a smart contract restricts who can call sensitive functions. Common patterns: a single owner address (Ownable), role-based permissions (OpenZeppelin's AccessControl), or multisig governance. The most common smart-contract bug class is missing access control — a function intended to be admin-only that has no modifier, allowing any address to call it. The fix is mechanical: every state-changing administrative function needs an `onlyOwner` modifier or equivalent require check.