Bueno.art A-2

Description

Tokens can be minted via mintToken, mintTokenTo, or mintTokenAllowlist functions. All of those functions call _mintAfterChecks to verify certain conditions before minting. The _mintAfterChecks function verifies the specified token id as follows:

if (id > _currentTokenId) {
    revert InvalidToken();
}

According to the check above, _currentTokenId can be minted because it only reverts for id greater than _currentTokenId. This is problematic because _currentTokenId refers to the next token ID that will be created (rather than the last token ID that has been created).

This allows for the minting of the next token ID before the actual token has been created through the createDropToken or createDropTokens functions.

Consider the following scenario: a creator calls createDropToken to create a token with an amount of 100 and a price of 10 ether. A malicious user could front-run the transaction and pre-mint all 100 tokens by specifying the _currentTokenId when calling mintToken. Since token settings are not yet set for the token with ID _currentTokenId, the user can mint all 100 tokens for free.

Remediations to Consider

Only allow minting of tokens for ids smaller than _currentTokenId.

Description

According to specification, maxSupply should behave as follows:

A token with 0 supply is considered to have infinite possible supply (though it can still be bounded by mintEnd)

However, the airdropTokenfunction contains the following logic:

if (updatedAmountMinted > token.maxSupply) {
    revert SoldOut();
}

As per the above logic, airdrops using tokens with maxSupply == 0 will revert with error SoldOut(). In addition, once a token has been minted, maxSupply can’t be changed anymore via updateTokenSettingsByIndex function - giving the issue a high severity impact.

Remediations to Consider

Only apply above revert logic when maxSupply > 0.

Description

As stated in the readme and checked in the _verifyPaymentSplitterSettings function, the sum of all payees shares must be 100:

if (shareTotal != 100) {
revert InvalidPaymentSplitterSettings();
}

This is correctly checked when adding payment settings via the initialize, updatePaymentSplitterSettingsByIndex, and updateFallbackPaymentSplitterSettings. However, the call to _verifyPaymentSplitterSettings is missing when creating tokens via createDropToken and createDropTokens. This allows creating payment settings that don’t comply to the contract’s invariant of shareTotal == 100.

This can have the following consequences:

1. Payees can be specified with shares == 0: Once a token with price > 0 gets minted, the paid ether is not added to the payee’s revenue - resulting in the paid amount being locked in the contract
2. Payees can be specified with shareTotal > 100: In this case, payees will receive revenue that exceeds the allocated amount for the associated token id. As a result, other payees will fail to release their entitled revenue as there is not sufficient ether amount left in the contract.

Note that specifying invalid payment settings can be set unintentionally by the owner, but can also happen due to a logic bug on the frontend (which is not uncommon).

Remediations to Consider

Verify payment settings in createDropToken and createDropTokens by adding _verifyPaymentSplitterSettings to these functions.

Description

In _mintAfterCheck, the following code validates the start/end time of minting:

if (
    (token.mintStart > 0 || token.mintEnd > 0) &&
    (block.timestamp < token.mintStart ||
        block.timestamp > token.mintEnd)
) {
    revert MintNotActive();
}

The specification defines tokens with mintEnd == 0 as follows:

A token with no mintEnd is assumed to be mintable forever

However, the above code breaks the specification as the line block.timestamp > token.mintEnd always evaluates to true when mintEnd is not specified, resulting in the transaction to revert. As a consequence, tokens with no mintEnd specified can’t be minted.

Note that the impact of this issue is considered low severity, as it can be remedied by updating token settings via updateTokenSettingsByIndex.

Remediations to Consider

Change above logic so that tokens with startEnd > 0 and mintEnd == 0 are not being reverted.

Description

An overflow can happen in _mintAfterChecks on the following lines:

unchecked {
    token.amountMinted += quantity;
    _mintBalanceByTokenId[id][account] += quantity; 
}

A malicious user can cause an overflow on amountMinted by minting more than max(uint32)-1 tokens. This results in incorrect accounting of amountMinted, which can have various consequences, such as:

1. The number of minted tokens can exceed maxSupply, which breaks the protocol's invariant of amountMinted ≤ maxSupply.
2. An attacker can trick the creator into assuming that no tokens have been minted. Consider the following scenario:
   1. The creator creates a token with an infinite supply (maxSupply = 0).
   2. A malicious user takes advantage of overflow and mints max(uint32) tokens, thereby setting amountMinted back to 0.
   3. As amountMinted is now equal to 0, the creator wrongly assumes that no tokens have been minted so far and may change the max supply or set the price > 0.
   4. The creator holds a number of tokens equal to max(uint32), which suddenly become worth a fortune.

Remediations to Consider

Don’t use unchecked arithmetic in above code logic.

Description

The airdropToken function iterates over an array of provided recipients and mints the respective tokens to each recipient. During mint, if the recipient is a contract, ERC1155Upgradeable.sol calls onERC1155Received and gives execution control to the recipient contract. This means that the recipient contract can execute malicious code, such as consuming all the provided gas. If this occurs, calls to airdropToken could cost substantially more than expected or exceed the block gas limit, preventing calls from executing.

The impact of this vulnerability is considered low severity, as airdropToken can be called again by omitting the griefer contract.

Remediations to Consider

• Switch from a push method of transferring tokens, to a pull method. This makes users claim their airdrop and prevents malicious users from preventing others from receiving theirs.
• Or explicitly pass in the amount of gas for the transfer, ensuring there is enough gas to allow the contract to execute normal operations, but not provide the entire gas of the transaction that can be used maliciously.

Description

The releaseBatch function iterates over the provided payees array and calls release for each payee. However, if a payee has already released the funds, a call to release will revert and cause the entire releaseBatch function to fail.

uint256 amount = releasable(payee); 

if (amount == 0) {
    revert NoFundsToRelease();
}

Remediations to Consider

Don’t revert for amount == 0 in release function.

Description

In updateTokenSettingsByIndexand updatePaymentSplitterSettingsByIndex, the following check should prevent non-existing token ids from being updated:

if (id > _currentTokenId) {
    revert InvalidToken();
}

According to the check above, updates to _currentTokenId are allowed. However, _currentTokenId has not yet been created and refers to the next token that will be created. Therefore, a subsequent call to createDropToken or createDropTokens would overwrite the previously defined settings.

Remediations to Consider

Only allow updates for token ids smaller than _currentTokenId.

Description

Token settings can be specified by calling initialize, createDropToken, and createDropTokens. However, these functions do not check whether the settings passed are valid. For instance, if a token is created with mintEnd < block.timestamp, no tokens can ever be minted. Similarly, if amountMinted > 0 on token creation, amountMinted would be wrongly tracked.

Remediations to Consider

Add validation checks to only allow meaningful token settings.

Consider renaming the index parameter to id in the airdropToken function to match the naming convention used in all the other functions parameter.

In calculateRevenueSplit function, there is the following comment:

// each token can have different payment splitter settings, and those settings can change while mint is occurring
// therefore we need to do some revenue accounting at the time of mint based on the price paid

However, this comment is incorrect, since payment splitter settings cannot be modified after a token has been minted.

Generally it is considered a good practice to emit an event on state changes. Consider emitting an event when fallBackPaymentSplitterSettings are being changed.

totalReleased() is defined as public but not used anywhere else in code. Consider saving gas costs by using external keyword instead of public.

In createDropTokens, uuid is stored in memory variable and only used once when emitting the event. Consider saving gas costs by using settings.uuid instead.

On every mint, amountMinted is increased by the number of minted tokens, thus increasing gas costs as a storage variable needs to be updated. At the same time, ERC1155SupplyUpgradeable tracks the totalSupply per token id. Consider removing amountMinted and use totalSupply(uint256 id) instead to save gas costs.

Each token created via the Bueno1155Drop contract is assigned a unique UUID to identify it within the Bueno ecosystem. It is important to note that the uniqueness of the UUID is not checked on-chain and relies on properly functioning off-chain components.