Integer Overflow

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Pronunciation

[in-tuh-jer oh-ver-floh]

Analogy

Integer overflow is like an odometer rolling past its maximum reading and resetting to zero.

Definition

A vulnerability where arithmetic operations exceed the maximum value of a data type, wrapping around to zero or a lower value.

Key Points Intro

Overflows occur due to fixed‑width arithmetic via:

Key Points

Wrapping behavior: Values modulo 2ⁿ for n‑bit types.

Unchecked operations: Default in Solidity ≥0.8 rolls back on overflow.

Legacy risk: Pre‑0.8 required SafeMath to guard.

Attack vector: Manipulate balances or loop counters.

Example

``` uint8 x = 255; x += 1; // x becomes 0 without error in older ```

Technical Deep Dive

`ADD` and `MUL` opcodes wrap on overflow. ≥0.8 inserts runtime checks that revert on overflow via `INVALID` opcode. SafeMath library uses `require` to enforce bounds in earlier versions.

Security Warning

Rely on compiler checks or SafeMath to prevent silent overflows.

Caveat

Unchecked blocks (`unchecked { }`) disable overflow checks—use cautiously.

Related Terms

Integer Underflow

EVM

Gas Optimization

Blockchain & Cryptocurrency Glossary

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