QA Report

[code423n4]

QA Findings (low / non-critical)

[Q-1] Gobblers Can Gobble Themselves Via Wrappers

Affected files:

• src/ArtGobblers.sol

Description:
The gobble method attempts to block Gobbler's gobbling other gobblers, however this can be circumvented by creating a Gobbler wrapping contract, bypassing the msg.sender == address(this) check.

Recommendation:
This issue is relatively hard to mitigate without negatively impacting the immutability of Gobblers. However if the inability for Gobblers to gobble other Gobblers is strongly desired novel subjective dispute resolution mechanisms aka "decentralized courts" like Kleros may be used to enforce such restrictions without too heavily impacting the immutability and decentralization of Gobblers.

[Q-2] legendaryGobblerPrice Reports Price Even After Legendary Gobblers Sell Out

Affected files:

• src/ArtGobblers.sol

Description:
The legendaryGobblerPrice method still reports a price even after all 10 legendary Gobblers have been sold. This may lead to unforeseen consequences or even bugs in downstream applications such as e.g. price oracles who may directly depend on the value.

Recommendation:
It is recommended the legendaryGobblerPrice method be changed so that it either returns type(uint256).max once all Gobblers have sold out to indicate they can no longer be purchased with Gobblers, or that the method simply reverts. The method could also be left as is as this has no direct effect on the ArtGobblers contract itself, however this fact should then definitely be documented to ensure developers can plan for any potential resulting edge cases in their applications.

[Q-3] Randomness Provider Upgrade Can Be Temporarily Blocked and Delayed

Affected files:

• src/ArtGobblers.sol

Description:
If the owner of the ArtGobblers contract attempts a random provider upgrade an attacker may revert the upgrade transaction and temporarily prevent it from being called for a short "blackout window". This can be achieved by front-running calls to upgradeRandProvider with a call to requestRandomSeed. Exploiting this also requires that the requestRandomSeed cooldown has expired.

The upgrade blackout window can open any time as soon the reveal cooldown expires and lasts from when the new seed is requested until that request is fulfilled. The upgrade blackout window may be extended by an attacker via block stuffing or other attacks against the randomness provider mechanism or even the Ethereum network itself.

This may not be so critical if an upgrade is required because e.g. Chainlink VRF v1 is sunset which would likely come with days if not months of advanced notice. However in a scenario where a critical vulnerability is discovered in the randomness provider it may be much more critical to upgrade it in a timely manner, an added delay of even a couple blocks could allow an attacker to cause substantial additional damage depending on the vulnerability discovered.

Note on severity: Due to the requirement for a particular class of randomness provider vulnerabilities which do not seem to currently exist in Chainlink VRF v1 this issue has been deemed as "low".

Recommendation:
Require new randomness always be requested in two steps: 1. inititate seed request 2. request seed. A minimum delay between the two steps should be enforced. This will ensure that as long as the seed request has not been initiated the owner can easily complete a randomness provider upgrade without worrying about race conditions. Note that this is still vulnerable to block stuffing attacks. Alternatively always allow the owner to upgrade the randomness provider regardless of whether an existing request is in progress, this comes at the tradeoff of allowing the owner to intervene in existing requests.

[Q-4] NFT-Based Authentication Limited To Direct Ownership Check

Affected files:

• src/ArtGobblers.sol L437, L733

Description:
The gobble and mintLegendaryGobbler methods require callers to be the direct owners of the Gobblers they wish to engage in the given method and no not consider token or operator approvals. Checking approvals as fallback to direct ownership is recommended as it allows integrating smart contracts to more easily and cheaply perform operations on behalf of users because contracts do not have to transfer the Gobbler tokens to themselves first and subsequently return them.

Recommendation:
Use a check similar to L890, first checking direct ownership and falling back to approval in the gobble and mintLegendaryGobbler methods. Consider renaming or adding fields to the ArtGobbled events so that the operator / owner at the time can be discerned. Furthermore, for this change in the mintLegendaryGobbler ensure that the owners' (not the operators') lastBalance, lastTimestamp, emissionMultiple and gobblersOwned are changed in the loop as the caller i.e. operator may only have approval and subsequently be using Gobblers from multiple different owners.

[Q-5] Non-Standard Naming

Affected files:

• src/utils/rand/RandProvider.sol
• src/ArtGobblers.sol

Description:

• src/utils/rand/RandProvider.sol: Interface name and file RandProvider not prefixed with 'I'
• src/ArtGobblers.sol: Internal method updateUserGooBalance not prefixed with underscore to indicate it's internal.

Recommendation:
It is recommended to follow typical naming conventions for the sake of improved readability unless there's some express purpose for the unconventional style in the two instances.

[Q-6] Lack Of multicall

Affected files:

• src/ArtGobblers.sol
• src/Pages.sol
• src/Goo.sol

Description:
The listed files do not implement a multicall method. This is highly recommended for contracts that do not interact directly with ETH. While the only downside is an increase in code size, it does have potential to massively improve UX by allowing EOAs to do multiple actions on the contracts in a single transaction.

Recommendation:
Implement a multicall method for the mentioned contracts. The OpenZeppelin contracts or solady libraries have good implementations in this regard.

[Q-7] Docs / Code Discrepancy

Affected files:

• src/ArtGobblers.sol
• README.md

Description:
On L213 the readme claims that "Art Gobblers themselves are fully animated ERC1155 NFTs." The ArtGobblers contract however only implements the ERC721 standard and not ERC1155.

Recommendation:
Correct this discrepancy and remove any unused files such as src/utils/token/GobblersERC1155B.sol .

[Q-8] Owned Mixin Implements ERC173 Functionality But Does Not Adhere To The Standard

Affected files:

• lib/solmate/src/auth/Owned.sol
• src/ArtGobblers.sol
• src/utils/GobblerReserve.sol

Description:
The Owned contract and subsequently the contracts that inherit from it implement ERC173 functionality (single owner address, transferability, emitted event upon transfer) but do not adhere to its signatures.

Recommendation:
It is recommended to comply with the ERC173 standard as it comes at no added cost but does improve potential interoperability with other applications. Rename the setOwner method to transferOwnership and the OwnerUpdated event to OwnershipTransferred in order to be ERC173 compliant.

[Q-9] GobblerReserve Cannot Accept Gobblers Sent As A Safe Transfer

Affected files:

• src/utils/GobblerReserve.sol

Description:
Considering GobblerReserve is meant to hold Gobblers on behalf of others it may be wise to allow it to receive Gobblers via safe transfers depending on how it is intended for users to potentially use this contract.

Recommendation:
Implement the ERC721 onERC721Received hook and check that the contract is the Art Gobblers to ensure that users can deposit Gobblers into reserve contracts.

[Q-10] Inconsistent Error Style

Affected files:
Overall repo including but not limited to:

• src/ArtGobblers.sol
• src/utils/token/GobblersERC721.sol

Description:
Throughout the repo both custom errors and the default string errors (Error(string)) are used.

Recommendation:
For the sake of consistency and readability it is recommended one style of errors is chosen and kept consistent throughout the repo.

[GalloDaSballo]

[Q-1] Gobblers Can Gobble Themselves Via Wrappers

NC

[Q-2] legendaryGobblerPrice Reports Price Even After Legendary Gobblers Sell Out

R

[Q-3] Randomness Provider Upgrade Can Be Temporarily Blocked and Delayed

TODO Dup of #153

[Q-4] NFT-Based Authentication Limited To Direct Ownership Check

R

[Q-5] Non-Standard Naming

R

[Q-6] Lack Of multicall

Would have liked more detail, NC

[Q-7] Docs / Code Discrepancy

NC

[Q-8] Owned Mixin Implements ERC173 Functionality But Does Not Adhere To The Standard

TIL, R (why is this a standard?)

[Q-9] GobblerReserve Cannot Accept Gobblers Sent As A Safe Transfer

NC they can still receive via normal transfer

[Q-10] Inconsistent Error Style

R

Really nice human written report, which is unique, good work!

5R 3NC

[GalloDaSballo]

Only report I gave bonus points to for uniqueness