omermaksutii/rugproof/integer-issues

Integer issues detection

When this applies

• unchecked { … } blocks (Solidity ≥0.8)
• Downcasts: uint128(x), int256(uint256(x)), uint8(...)
• Division and modulo
• Fixed-point math with custom decimal scales
• Share/asset math in vaults, lending, AMMs
• Pre-0.8 Solidity code (no built-in overflow checks)
• Vyper code with unbounded loops
• Inline assembly arithmetic

Detection patterns

Unchecked overflow on user input (HIGH)

unchecked {
    balance[to] += amount;        // ← if amount controlled, can overflow back to 0
}

unchecked is fine for proven-safe accumulators (e.g. ++i in bounded loops), not for value math.

Division before multiplication (HIGH)

uint256 fee = (amount / 100) * feeBps;   // ← truncation; do (amount * feeBps) / 100

Decimal mismatch (HIGH)

USDC = 6 decimals, WETH = 18, WBTC = 8. Mixing without scaling produces silent 1e10–1e12 errors.

uint256 wethValue = amountUsdc * price;   // ← USDC 6dp × price 8dp = 14dp, need 18dp

Downcast loss (HIGH)

uint128 sharesU128 = uint128(shares);   // ← silently truncates if shares > 2^128

Use OZ SafeCast.

Fixed-point precision loss (HIGH)

Compounding interest done as principal * (1 + rate)^t with too-few-decimal rate. Use ray (1e27) or wad (1e18) math via PRBMath / Solady.

Round-direction asymmetry (HIGH for vaults)

ERC-4626 must round shares down on deposit (favor vault) and up on withdraw (favor vault). Reversed direction = donations-style drain. Use OZ Math.mulDiv(_, _, _, Rounding.Down/Up).

Signed/unsigned mixing (HIGH)

int256 delta = int256(a) - int256(b);   // a or b might be > 2^255, becomes negative silently

Modulo zero (revert, but…) (MEDIUM-HIGH if attacker can set divisor=0)

Block-time math on L2 (MEDIUM)

block.timestamp granularity differs (2s on Optimism, 250ms on Arbitrum). Slot-based deadlines can be off.

Sqrt / log integer approximations (MEDIUM)

Custom sqrt implementations are notorious. Use Solady/PRBMath.

Percentage in basis points without bounds (LOW)

fee_bps should be capped (fee_bps <= 10_000).

Severity rubric

Remediation patterns

• Solidity 0.8.x default checks; only unchecked proven-safe (e.g. ++i in for loops bounded by array length).
• OZ SafeCast for downcasts.
• Math.mulDiv (OZ) for multiply-then-divide without intermediate overflow.
• PRBMath or Solady for fixed-point exp/log/pow.
• Always scale to a common decimal base before doing math; document the scale.
• ERC-4626: always use Math.mulDiv(..., Rounding.Down) on deposits, Rounding.Up on withdrawals; or use OZ's ERC4626Upgradeable which handles this.

False-positive notes

• unchecked { ++i; } in for loops with i < arr.length is the canonical safe use — not a finding.
• Pre-0.8 SafeMath is fine; the issue is mixed-version dependencies.

Related

• [[token-compatibility]] — decimals confusion
• [[oracle-manipulation]] — price scaling
• [[yield-aggregator-specialist]] — ERC-4626 round direction