ERC4626 Security checklist

Comprehensive Security Checklist for ERC4626 Standardized Yield Farming Vaults: A meticulously curated guide outlining essential security measures for developers engaging with the ERC4626 standard. This checklist offers a thorough examination of best practices and precautions to fortify the security posture of yield farming vaults, ensuring robust protection against potential threats and vulnerabilities

Created by @solthodox and @MaslarovK

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General Review Approach:

• Read the project's docs, specs, and whitepaper to understand what the smart contracts are meant to do.
• Construct a mental model of what you expect the contracts to look like before checking out the code.
• Do a generic line-by-line review of the contracts.
• Do another review from the perspective of every actor in the threat model.
• Glance over the project's tests + code coverage and look deeper at areas lacking coverage.
• Look at related projects and their audits to check for any similar issues or oversights.

Standard compliance

• SC1- Is the vault EIP20 compatible?
• SC2- Does assetreturn the address of the token that is deposited in the vault?
• SC3- Is asset a ERC20 compatible?

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• SC4- Does asset never revert?
• SC5- Does totalAssets always include the compounding that occurs from yield?
• SC6- Does totalAssets always include any fees externally charged to the vault?
• SC7- Does totalAssets never revert?

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• SC8- Do convertToAssets & convertToShares always include any fees externally charged to the vault?
• SC9- Do convertToAssets & convertToShares never vary depending on the caller?
• SC10- Do convertToAssets & convertToShares never exclude slippage,vault fees and other chain conditions?
• SC11- Do convertToAssets & convertToShares never revert, except for a overflow due to a big integer input or similar?
• SC12- Do convertToAssets & convertToShares always round down?

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• SC13- Does maxDeposit always return maximum amount of assets deposit would allow to be deposited for receiver?
• SC14- Does maxMint always return maximum amount of shares mint would allow to be minted for receiver?
• SC15- Do maxDeposit & maxMint always return 0 if deposits are disabled?
• SC16- Do maxDeposit & maxMint always return 2 ** 256 - 1 when there is no limit?
• SC17- Do maxDeposit & maxMint never relay on balanceOf of asset?
• SC18- Do maxDeposit & maxMint never revert?

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• SC19- Does previewDeposit always ignore the maxDeposit?
• SC20- Does previewMint always ignore the maxMint?
• SC21- Does previewDeposit always return same or fewer shares than those that would actually be minted on deposit?
• SC22- Does previewMint always return same or more assets than those that would actually be deposited on mint?
• SC23- Do previewDeposit & previewMint always include any vault deposit fees ?
• SC24- Do previewDeposit & previewMint never revert, except for a overflow due to a big integer input or similar?
• SC25- Do previewDeposit & previewMint always consider slippage and other chain conditions unlike convertToShares & convertToAssets?
• SC26- Does previewDeposit always round down ?
• SC27- Does previewMint always round up ?

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• SC28- Does deposit always pull exactly assets tokens?
• SC29- Does mint always mint exactly shares shares?
• SC30- Does deposit always mint exactly shares tokens?
• SC31- Does mint always return the exact amount of assets deposited?
• SC32- Does deposit always revert if the maxDeposit is exceeded?
• SC33- Does mint always revert if the maxMint is exceeded?
• SC34- Do deposit & mint always support the approve/transferFrom on asset as a deposit flow?
• SC35- Do deposit & mint always emit the Depositevent?

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• SC36- Does maxWithdraw always return the maximum amount of assets that a user can withdraw ?
• SC37- Does maxRedeem always return the maximum amount of shares that a user can redeem ?
• SC38- Do maxWithdraw & maxRedeem always return 0 if withdrawals are disabled?
• SC39- Do maxWithdraw & maxRedeem never revert?

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• SC40- Does previewWithdraw always round up?
• SC41- Does previewRedeem always round down?
• SC42- Does previewWithdraw always return same or more shares than those that would actually be burnt when performing a withdraw?
• SC43- Does previewWithdraw always return same or fewer assets than those that would actually be sent to the user when performing a withdraw?
• SC44- Does previewWithdraw always ignore the maxWithdraw?
• SC45- Does previewRedeen always ignore the maxRedeem?
• SC47- Do previewWithdraw & previewRedeen always include any vault withdrawal fee?
• SC48- Do previewWithdraw & previewRedeen always consider slippage and other chain conditions unlike convertToShares & convertToAssets?
• SC49- Do previewWithdraw & previewRedeen never revert except for other conditions that would make the withdraw & redeem revert?

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• SC50- Does withdraw always transfer exactly assets assets?
• SC51- Does redeem always burn exactly shares shares?
• SC52- Does withdraw always burn exactly shares shares?
• SC53- Does redeem always transfer exactly assets assets?
• SC54- Does withdraw always revert if assets exceeds maxMint?
• SC55- Does redeem always revert if shares exceeds maxRedeem?
• SC56- Do withdraw and redeem always allow to operate on behalf of another operator as long as there is an approval of his shares to the msg.sender that is decreased after the call?
• SC57- Do withdraw and redeem always emit the Withdraw function?

Math

• M1- Are all the roundings done in favor of the protocol to prevent any rounding vulnerability?
• M2- Are the multiplications done before the divisions?
• M3- Is the contract using a math library(e.g. OZ::Math) to make sure big operations don't overflow?
• M4- Can any value be maliciously inflated by sending assets to the vault?
• M5- If there is any entry or exit fee, is the inverse of the fee properly calculated when converting from assets to shares or vice versa?
• M6- If there is any decimal scalation, is it correctly done?
• M7- Can the vault properly handle the cases where there are zero shares, assets or even both?

External calls

• E1- Does the vault properly handle reverting calls to external dependencies?
• E2- Is the vault susceptible to suffering a gas grieffing due to this external calls?
• E3- Does the vault dangerously set a fixed gas limit when doing external calls?
• E4- If performing raw calls, does the contract check for the success return value?
• E5- If performing swaps, is the minimum tokens out parameter set to 0 to make sure the swaps always suceeds?
• E6 - If the vault incurs in losses in withdrawals because of slippage in swaps, does it have some kind of TVL limit so in case all the assets need to be liquidated the slippage is not crazy?

Share price

• SP1- Are totalAssets pesimistically accounted?
• SP2- Does the share price relay too much on external dependencies?
• SP3- Can the share price be manipulated by either vault users or vault's external dependencies(e.g. oracle manipulation)?
• SP4- Is the vault share price inflation attack safe?
• SP5- If there is any profit lock mechanism, is it correctly reflected in the share price?

Inheritance

• IC1- If the contracts inherits from ERC4626.sol and modifies some logic from the original implementation, does it override all of the needed functions from the inheriting for the vault to work properly?
• IC2- Is there any storage collision due to the inheritance?

Tokens

• T1- If the vault is intended to use any token, does it properly work with fee-on-transfer or rebase tokens?
• T2- Can some malicious token reenter the vault?
• T2- Can the contract be DoSed because an approval race conditon in the underlyig token?
• T2- If the vault is intended to use any token, does it use a safe transfers libary such as OZ::SafeERC20 to safely interact with those that dont have a return value or other cases?

Permissions and Access Control

• P1- Are there any constraints when it comes to fees or other values that can be set by a trusted role?
• P2- Can a trusted role steal funds from the vault?
• P3 - Will users' funds be locked if the vault is paused/shutdown?
• P4 - Do functions have a solid input validation?
• P6 - If the funds are invested in external protocols, does the vault have some kind of emergency mode where the needed positions can be fully liquidated if neeed?

General Security Practices

• G1- Does the contract try to keep the logic simple?
• G2- Does the contract implement battle-tested code?
• G3- Does the contract use a safe solidity pragma?
• G4- Do tests have a high(>=90%) code coverage?
• G5- If implementing external protocols, did the doing following the recommendations in the documentation?
• G6- Does the test suite have fuzz-tests as well?