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Integer Underflow

What it detects​

This detector looks for subtractions that could underflow in older Solidity versions or within unchecked blocks. When a smaller value is subtracted from zero, the result wraps to a huge number, corrupting balances.

Typical symptoms​

  • Balances balloon unexpectedly after deductions
  • Arithmetic inside unchecked sections using subtraction

Solidity snippet (v0.8.25)​

pragma solidity ^0.8.25;

contract Underflow {
    function dec(uint256 a, uint256 b) external pure returns (uint256) {
        unchecked {
            // Wraps to a large value on underflow
            return a - b;
        }
    }
}

Why it matters on EVM​

Underflow can grant attackers large balances or reset counters, leading to unauthorized withdrawals or logic errors.