Security Audit
July 3rd, 2023
Version 1.0.0
Presented by 0xMacro
This document includes the results of the security audit for Bueno.art's smart contract code as found in the section titled ‘Source Code’. The security audit was performed by the Macro security team from June 26th, 2023 to June 27th, 2023.
The purpose of this audit is to review the source code of certain Bueno.art Solidity contracts, and provide feedback on the design, architecture, and quality of the source code with an emphasis on validating the correctness and security of the software in its entirety.
Disclaimer: While Macro’s review is comprehensive and has surfaced some changes that should be made to the source code, this audit should not solely be relied upon for security, as no single audit is guaranteed to catch all possible bugs.
The following is an aggregation of issues found by the Macro Audit team:
Severity | Count | Acknowledged | Won't Do | Addressed |
---|---|---|---|---|
Low | 2 | - | - | 2 |
Code Quality | 3 | - | - | 3 |
Bueno.art was quick to respond to these issues.
Our understanding of the specification was based on the following sources:
The following source code was reviewed during the audit:
Specifically, we audited the following contracts within this repository:
Contract | SHA256 |
---|---|
contracts/Bueno1155Drop.sol |
|
contracts/Bueno721Drop.sol |
|
contracts/BuenoFactory.sol |
|
contracts/ICommon.sol |
|
Note: This document contains an audit of the differences between Solidity contracts listed above and previous version from Bueno-Art-2 audit. Specifically, the audit pertains only to the contracts themselves, and does not pertain to any other programs or scripts, including deployment scripts.
Click on an issue to jump to it, or scroll down to see them all.
We quantify issues in three parts:
This third part – the severity level – is a summary of how much consideration the client should give to fixing the issue. We assign severity according to the table of guidelines below:
Severity | Description |
---|---|
(C-x) Critical |
We recommend the client must fix the issue, no matter what, because not fixing would mean significant funds/assets WILL be lost. |
(H-x) High |
We recommend the client must address the issue, no matter what, because not fixing would be very bad, or some funds/assets will be lost, or the code’s behavior is against the provided spec. |
(M-x) Medium |
We recommend the client to seriously consider fixing the issue, as the implications of not fixing the issue are severe enough to impact the project significantly, albiet not in an existential manner. |
(L-x) Low |
The risk is small, unlikely, or may not relevant to the project in a meaningful way. Whether or not the project wants to develop a fix is up to the goals and needs of the project. |
(Q-x) Code Quality |
The issue identified does not pose any obvious risk, but fixing could improve overall code quality, on-chain composability, developer ergonomics, or even certain aspects of protocol design. |
(I-x) Informational |
Warnings and things to keep in mind when operating the protocol. No immediate action required. |
(G-x) Gas Optimizations |
The presented optimization suggestion would save an amount of gas significant enough, in our opinion, to be worth the development cost of implementing it. |
maxQuantity
is ignored when maxPerWallet
is exceeded
When minting through allowlist, maxQuantity
can be specified for specific wallets, allowing for more granular control over who can mint how many tokens. Meaning that maxQuantity
(on wallet-level) should take precedence over maxPerWallet
(on phase-level).
This is currently not the case due to the following check in the _checkAllowlistPhaseMintConditions
function:
if (
// phases can have a maxPerWallet
(phase.maxPerWallet > 0 && updatedAmountMinted > phase.maxPerWallet) ||
// wallets can have a maxPerWallet encoded in the merkle tree
(maxQuantity > 0 && updatedAmountMinted > maxQuantity)
) {
revert ExceedMaxPerWallet();
}
With the above logic, the transaction reverts when maxPerWallet
is set and exceeds the amount of mints. Thus, it doesn’t support the case when specific wallets should be allowed to mint more (via maxQuantity
) than the mint limit set on phase-level (via maxPerWallet
).
Consider changing the above logic so that maxPerWallet
is ignored when maxQuantity
is specified.
In Bueno721Drop.mintBatch
users can pay more than needed when publicQuantity
is set to 0
. After the for
loop, the following is checked when publicQuantity > 0
:
if (publicQuantity > 0) {
_checkPublicMintConditions(publicQuantity, balance);
...
In this case, overpay is not possible as the balance is checked accordingly inside the _checkPublicMintConditions
function. However, if publicQuantity = 0
, there is no further check for the remaining balance.
Consider checking that there is no balance left (balance = 0
) after the for-loop when publicQuantity = 0
.
The documentation says:
updatePhaseSettings
allows the creator to change all of the conditions of their minting phase, with the exception ofamountMinted
andmaxSupply
In addition to the above, isActive
also cannot be changed via updatePhaseSettings
.
When compiling the Bueno721Drop
contract, the compiler outputs the following message:
Warning: Contract code size is 25037 bytes and exceeds 24576 bytes (a limit introduced in Spurious Dragon). This contract may not be deployable on Mainnet. Consider enabling the optimizer (with a low "runs" value!), turning off revert strings, or using libraries.
--> contracts/Bueno721Drop.sol:49:1:
|
49 | contract Bueno721Drop is
| ^ (Relevant source part starts here and spans across multiple lines).
Saying that the contract size must not exceed the limit of 24576 bytes. Besides using proxy patterns such as Diamond proxy to address the issue with the maximum size, there are a couple of others, more simpler, solutions on how to reduce the contract size:
Lowering number of runs
Runs: 20
·---------------------------------|--------------------------------|--------------------------------·
| Solc version: 0.8.17 · Optimizer enabled: true · Runs: 20 │
··································|································|·································
| Contract Name · Deployed size (KiB) (change) · Initcode size (KiB) (change) │
··································|································|·································
| Bueno1155Drop · 22.332 () · 22.570 () │
··································|································|·································
| Bueno721Drop · **23.998 ()** · 24.236 () │
·---------------------------------|--------------------------------|--------------------------------·
Enabling viaIR
flag
Runs: 20
and viaIR: true
·---------------------------------|--------------------------------|--------------------------------·
| Solc version: 0.8.17 · Optimizer enabled: true · Runs: 20 │
··································|································|·································
| Contract Name · Deployed size (KiB) (change) · Initcode size (KiB) (change) │
··································|································|·································
| Bueno1155Drop · 20.838 (-0.407) · 21.037 (-0.407) │
··································|································|·································
| Bueno721Drop · **22.617 (-0.778)** · 22.816 (-0.778) │
·---------------------------------|--------------------------------|--------------------------------·
Further details about viaIR
flag can be found here.
Refactor code to reuse redundant code blocks
Use _mintPhaseTo()
and _mintPublicTo()
helper functions
mintPhaseAllowlist()
, mintPhase()
and mintPhaseTo()
share common functionality that can be abstracted away into one internal function _mintPhaseTo()
. It would result in the following code:
/**
* @notice Mint tokens for an allowlisted phase
* @dev Calling this function for a phase that doesn't have an allowlist will fail
*/
function mintPhaseAllowlist(
uint256 phaseIndex,
uint64 quantity,
uint32 maxQuantity,
bytes32[] calldata proof
) external payable {
uint64 updatedAmountMinted = _checkAllowlistPhaseMintConditions(
quantity,
maxQuantity,
proof,
phaseIndex,
msg.value
);
_mintPhaseTo(msg.sender, quantity, phaseIndex, updatedAmountMinted);
}
/**
* @notice Mint tokens for a non-allowlist phase.
* @dev Calling this function for a phase that has an allowlist will fail
*/
function mintPhase(uint256 phaseIndex, uint64 quantity) external payable {
uint64 updatedAmountMinted = _checkPhaseMintConditions(
msg.sender,
quantity,
phaseIndex,
msg.value
);
_mintPhaseTo(msg.sender, quantity, phaseIndex, updatedAmountMinted);
}
/**
* @notice Mint a token to a specific address from a non-allowlisted sale phase
* @dev Useful in case the recipient of the tokens is not the sender (gifting, fiat checkout, etc)
*/
function mintPhaseTo(
address account,
uint256 phaseIndex,
uint64 quantity
) external payable {
uint64 updatedAmountMinted = _checkPhaseMintConditions(
account,
quantity,
phaseIndex,
msg.value
);
_mintPhaseTo(account, quantity, phaseIndex, updatedAmountMinted);
}
/**
* @notice Mint tokens for a given phase
* @param account The address to mint the tokens to
* @param quantity The number of tokens to mint
* @param phaseIndex The index of the phase to mint from
* @param updatedAmountMinted The updated amount minted for the phase
*/
function _mintPhaseTo(
address account,
uint64 quantity,
uint256 phaseIndex,
uint64 updatedAmountMinted
) internal {
_checkGlobalPerWalletMax(account, quantity);
saleState.phases[phaseIndex].amountMinted += quantity;
amountMintedForPhase[account][phaseIndex] = updatedAmountMinted;
_mint(account, quantity);
emit TokensMinted(account, quantity);
}
Similarly, mintPublic()
and mintPublicTo()
also share repeated functionality which can be extracted out into internal helper function _mintPublicTo()
, as such:
/**
* @notice Mint tokens in the public sale
*/
function mintPublic(uint64 quantity) external payable {
_mintPublicTo(msg.sender, quantity);
}
/**
* @notice Mint a token to a specific address from the public sale
* @dev Useful in case the recipient of the tokens is not the sender (gifting, fiat checkout, etc)
*/
function mintPublicTo(address account, uint64 quantity) external payable {
_mintPublicTo(account, quantity);
}
/**
* @notice Mint tokens in the public sale
* @param account The address to mint the tokens to
* @param quantity The number of tokens to mint
*/
function _mintPublicTo(address account, uint64 quantity) internal {
uint64 updatedAmountMinted = _checkPublicMintConditions(
quantity,
msg.value
);
_checkGlobalPerWalletMax(account, quantity);
baseSettings.amountMinted = updatedAmountMinted;
_mint(account, quantity);
emit TokensMinted(account, quantity);
}
Our tests have shown that the contract size can be reduced to 22.4 KB by applying above optimizations.
wallet
parameter in _checkAllowlistPhaseMintConditions()
In Bueno721Drop.sol, on line 698, msg.sender
is used to verify that a given wallet is in allowlist. And later, on line 704, wallet
parameter is used to check the amount of NFTs a given wallet has minted.
In both mintPhaseAllowlist
and mintBatch
when _checkAllowlistPhaseMintConditions()
is called the wallet
parameter that is being passed refers to msg.sender
i.e:
function mintPhaseAllowlist(...) external payable {
uint64 updatedAmountMinted = _checkAllowlistPhaseMintConditions(
msg.sender,
quantity,
maxQuantity,
proof,
phaseIndex,
msg.value
);
...
}
function mintBatch(...) external payable { ...
if (phase.merkleRoot == bytes32(0)) {
...
} else {
updatedAmount = _checkAllowlistPhaseMintConditions(
msg.sender,
quantity,
maxQuantity,
proof,
phaseIndex,
priceForPhase
);
}
}
Consider removing wallet
parameter from _checkAllowlistPhaseMintConditions()
entirely, and use msg.sender
instead. This improves readability, saves a little gas, and reduces the contract’s bytecode size.
Macro makes no warranties, either express, implied, statutory, or otherwise, with respect to the services or deliverables provided in this report, and Macro specifically disclaims all implied warranties of merchantability, fitness for a particular purpose, noninfringement and those arising from a course of dealing, usage or trade with respect thereto, and all such warranties are hereby excluded to the fullest extent permitted by law.
Macro will not be liable for any lost profits, business, contracts, revenue, goodwill, production, anticipated savings, loss of data, or costs of procurement of substitute goods or services or for any claim or demand by any other party. In no event will Macro be liable for consequential, incidental, special, indirect, or exemplary damages arising out of this agreement or any work statement, however caused and (to the fullest extent permitted by law) under any theory of liability (including negligence), even if Macro has been advised of the possibility of such damages.
The scope of this report and review is limited to a review of only the code presented by the Bueno.art team and only the source code Macro notes as being within the scope of Macro’s review within this report. This report does not include an audit of the deployment scripts used to deploy the Solidity contracts in the repository corresponding to this audit. Specifically, for the avoidance of doubt, this report does not constitute investment advice, is not intended to be relied upon as investment advice, is not an endorsement of this project or team, and it is not a guarantee as to the absolute security of the project. In this report you may through hypertext or other computer links, gain access to websites operated by persons other than Macro. Such hyperlinks are provided for your reference and convenience only, and are the exclusive responsibility of such websites’ owners. You agree that Macro is not responsible for the content or operation of such websites, and that Macro shall have no liability to your or any other person or entity for the use of third party websites. Macro assumes no responsibility for the use of third party software and shall have no liability whatsoever to any person or entity for the accuracy or completeness of any outcome generated by such software.