Integer Overflow & Access Control

Before Solidity 0.8.0, integer operations could silently overflow or underflow. Since 0.8.0, arithmetic reverts on overflow by default. However, using `unchecked {}` blocks (for gas optimization) re-enables this risk. Access control bugs are equally dangerous: missing `onlyOwner` modifiers, incorrect role checks, or forgetting to restrict initialization functions. Always use OpenZeppelin's AccessControl or Ownable. Common tools for finding vulnerabilities: Slither (static analysis), Mythril (symbolic execution), and Foundry's fuzzing.