sui-move-security

Sui Move Security — OpenZeppelin Contracts for Sui

Purpose

In May 2025 a single flawed overflow check in a shared math library — a checked_shl-class function that silently passed a value it should have rejected — led to the Cetus exploit: ~$223M drained from the largest DEX on Sui, and a corrupted fixed-point intermediate that multiple downstream protocols depended on. The lesson is structural, not incidental: value-path math and privileged-capability handling must come from audited primitives, never be hand-rolled.

OpenZeppelin Contracts for Sui (MIT) is that library. This skill is the map; the SSOT is upstream — start from the machine-readable entry point when you need detail: https://raw.githubusercontent.com/OpenZeppelin/contracts-sui/main/llms.txt

Hard rules (apply to every Move review and every new module)

1. Never write (a * b) / c manually. The intermediate product overflows even when the final result would fit. Use mul_div (widens internally, returns Option). Power-of-two denominator (Q64.64 / tick math)? Use mul_shr — the Cetus exploit lived in exactly this operation class.
2. Rounding is a protocol decision, not a detail. Every OZ divide/shift/ root takes an explicit RoundingMode — there is no default. Rule of thumb: round down on protocol-to-user payouts (vault shares both directions — the vault keeps the remainder), up only for conservative upper bounds the protocol absorbs, nearest() for quotes/display. If a deposit rounds up or a withdrawal rounds up, you built a drain loop.
3. Handle the Option at the boundary. Overflow-prone ops return Option<T>: abort with a domain error (.destroy_or!(abort EMathOverflow)), cap at a safe value, or propagate — but never destroy_some() blind.
4. Never shift with << / >> on value paths. Move's native shifts silently discard bits. checked_shl / checked_shr return None when any non-zero bit would be lost.
5. (a + b) / 2 overflows near type max — use average(a, b, mode).
6. Decimal conversions go through decimal_scaling (safe_upcast_balance / safe_downcast_balance) — never a hand-written * 10^k. Downcasts truncate; if the remainder matters, capture it before the downcast.
7. u64 is the standard width (Sui coin balances, timestamps, gas). Reach for u128/u256 only when the domain demands it; never use u512 directly (it exists for the library's internal widening).
8. Privileged capabilities need transfer policies. Raw transfer::transfer(admin_cap, new_owner) is a one-shot, typo-fatal handoff. Use openzeppelin_access (two-step approvals, time-locked transfers); for delayed privileged ops, openzeppelin_timelock.

Install (Move.toml — MVR, pin stable releases)

[dependencies]
openzeppelin_math = { r.mvr = "@openzeppelin-move/integer-math" }
openzeppelin_fp_math = { r.mvr = "@openzeppelin-move/fixed-point-math" }
openzeppelin_access = { r.mvr = "@openzeppelin-move/access" }
openzeppelin_utils = { r.mvr = "@openzeppelin-move/utils" }

Verify with sui move build. Each package ships compilable examples under its examples/ dir — read them before wiring (composition recipes, not docs prose).

The package map (which one for which job)

Canonical snippet (fee quote, from the OZ docs)

module my_sui_app::pricing;

use openzeppelin_math::{rounding, u64};

const EMathOverflow: u64 = 0;

public fun quote_with_fee(amount: u64): u64 {
    u64::mul_div(amount, 1025u64, 1000u64, rounding::nearest())
        .destroy_or!(abort EMathOverflow)
}

Review checklist (auditing a Sui Move package)

• Any manual * followed by / on a value path → replace with mul_div.
• Any <</>> on amounts, prices, or liquidity → checked_shl/checked_shr.
• Every rounding direction stated and justified (who absorbs the remainder?).
• Every Option-returning call handled explicitly (no blind unwraps).
• Decimal conversions centralized through decimal_scaling.
• Admin/owner capabilities transferred via openzeppelin_access policies.
• Unbounded mint/spend/call paths → rate limiter or allowance vault.
• Deps pinned via MVR; sui move build + sui move test green.

Pointers (read on demand — never vendor these into your repo)

• llms.txt (entry point): https://raw.githubusercontent.com/OpenZeppelin/contracts-sui/main/llms.txt
• Integer math guide (the rounding/overflow doctrine): https://docs.openzeppelin.com/contracts-sui/1.x/math
• Package catalogs: contracts/ · math/
• Audits + scope: https://github.com/OpenZeppelin/contracts-sui/tree/main/audits
• OZ's own caveat: the library is audited but young ("experimental software") — using it is not a substitute for auditing YOUR package.
• General Move skills (object model, PTBs, testing): npx skills add mystenlabs/skills --all