Max allowance restriction can be bypassed both for addresses for WL and public distributions due to reentrancy in mint function

[c4-submissions]

Lines of code

https://github.com/code-423n4/2023-10-nextgen/blob/8b518196629faa37eae39736837b24926fd3c07c/smart-contracts/NextGenCore.sol#L193-L200
https://github.com/code-423n4/2023-10-nextgen/blob/8b518196629faa37eae39736837b24926fd3c07c/smart-contracts/NextGenCore.sol#L227-L232
https://github.com/code-423n4/2023-10-nextgen/blob/8b518196629faa37eae39736837b24926fd3c07c/smart-contracts/MinterContract.sol#L213-L217
https://github.com/code-423n4/2023-10-nextgen/blob/8b518196629faa37eae39736837b24926fd3c07c/smart-contracts/MinterContract.sol#L234-L237

Vulnerability details

Impact

It is possible to bypass max allowance restriction both for WL addresses and public ones. Since getting whitelisted usually is not that easy and it takes time and effort, bypassing allowance restrictions for WL is pretty serious.

Proof of Concept

To mint a token, users would call the MinterContract.mint() function. First, it checks whether number of tokens minter does not exceeds max allowance. Then, it call the mint function in the NextGenCore contract, which calls the _mintProcessing.

    function _mintProcessing(uint256 _mintIndex, address _recipient, string memory _tokenData, uint256 _collectionID, uint256 _saltfun_o) internal {
        tokenData[_mintIndex] = _tokenData;
        collectionAdditionalData[_collectionID].randomizer.calculateTokenHash(_collectionID, _mintIndex, _saltfun_o);
        tokenIdsToCollectionIds[_mintIndex] = _collectionID;
        _safeMint(_recipient, _mintIndex);
    }

The _safeMint() checks if recipient refers to a smart-contract. If it does, then it makes an external call to its onERC721Received() function, which must return a magic value. However, this allows a minter to reenter MinterContract.mint() function and mint as many tokens as they want since the tokensMintedAllowlistAddress mapping is updated only AFTER the _safeMint() is invoked.

    function mint(uint256 mintIndex, address _mintingAddress , address _mintTo, string memory _tokenData, uint256 _saltfun_o, uint256 _collectionID, uint256 phase) external {
        require(msg.sender == minterContract, "Caller is not the Minter Contract");
        collectionAdditionalData[_collectionID].collectionCirculationSupply = collectionAdditionalData[_collectionID].collectionCirculationSupply + 1;
        if (collectionAdditionalData[_collectionID].collectionTotalSupply >= collectionAdditionalData[_collectionID].collectionCirculationSupply) {
            _mintProcessing(mintIndex, _mintTo, _tokenData, _collectionID, _saltfun_o);
            if (phase == 1) { //@audit updated after _safeMint() is invoked
                tokensMintedAllowlistAddress[_collectionID][_mintingAddress] = tokensMintedAllowlistAddress[_collectionID][_mintingAddress] + 1;
            } else {
                tokensMintedPerAddress[_collectionID][_mintingAddress] = tokensMintedPerAddress[_collectionID][_mintingAddress] + 1;
            }
        }
    }

So this two requirements won't work:

require(_maxAllowance >= gencore.retrieveTokensMintedALPerAddress(col, _delegator) + _numberOfTokens, "AL limit");
...
require(_maxAllowance >= gencore.retrieveTokensMintedALPerAddress(col, msg.sender) + _numberOfTokens, "AL limit");

Tools Used

Manual Review

Recommended Mitigation Steps

Add the non-reentrant modifier to the MinterContract.mint() function.

Assessed type

Reentrancy

[c4-pre-sort]

141345 marked the issue as duplicate of #51

[c4-pre-sort]

141345 marked the issue as duplicate of #1742

[c4-judge]

alex-ppg marked the issue as satisfactory

[c4-judge]

alex-ppg marked the issue as partial-50

[c4-judge]

alex-ppg marked the issue as satisfactory