Deactivated tiers can still mint reserve tokens, even if no non-reserve tokens were minted.

[code423n4]

Lines of code

https://github.com/jbx-protocol/juice-nft-rewards/blob/f9893b1497098241dd3a664956d8016ff0d0efd0/contracts/JBTiered721DelegateStore.sol#L808

Vulnerability details

Description

Tiers in Juicebox can be deactivated using the adjustTiers() function. It makes sense that reserve tokens may be minted in deactivated tiers, in order to be consistent with already minted tokens. However, the code allows the first reserve token to be minted in a deactivated tier, even though there was no previous minting of that tier.

function recordMintReservesFor(uint256 _tierId, uint256 _count)
  external
  override
  returns (uint256[] memory tokenIds)
{
  // Get a reference to the tier.
  JBStored721Tier storage _storedTier = _storedTierOf[msg.sender][_tierId];
  // Get a reference to the number of reserved tokens mintable for the tier.
  uint256 _numberOfReservedTokensOutstanding = _numberOfReservedTokensOutstandingFor(
    msg.sender,
    _tierId,
    _storedTier
  );
  if (_count > _numberOfReservedTokensOutstanding) revert INSUFFICIENT_RESERVES();
  ...
  for (uint256 _i; _i < _count; ) {
  // Generate the tokens.
  tokenIds[_i] = _generateTokenId(
    _tierId,
    _storedTier.initialQuantity - --_storedTier.remainingQuantity + _numberOfBurnedFromTier
  );
  unchecked {
    ++_i;
  }
}

function _numberOfReservedTokensOutstandingFor(
  address _nft,
  uint256 _tierId,
  JBStored721Tier memory _storedTier
) internal view returns (uint256) {
  // Invalid tier or no reserved rate?
  if (_storedTier.initialQuantity == 0 || _storedTier.reservedRate == 0) return 0;
  // No token minted yet? Round up to 1.
  // ******************* BUG HERE *********************
  if (_storedTier.initialQuantity == _storedTier.remainingQuantity) return 1;
  ...
}

Using the rounding mechanism is not valid when the tier has been deactivated, since we know there won't be any minting of this tier.

Impact

The reserve beneficiary receives an unfair NFT which may be used to withdraw tokens using the redemption mechanism.

Tools Used

Manual audit

Recommended Mitigation Steps

If Juicebox intends to use rounding functionality, pass an argument isDeactivated which, if true, deactivated the rounding logic.

[Picodes]

The finding illustrates how a reserve token could be minted for a removed tier, and this token used to redeem funds.

[c4-judge]

Picodes marked the issue as satisfactory

[thereksfour]

@Picodes This one seems to be a subset of this finding https://github.com/code-423n4/2022-10-juicebox-findings/issues/191

[Picodes]

Thank you for flagging, I will think about it!

[Picodes]

Although it is in the same lines and functionalities, I don't think this one is a subset of #191: this one is about the fact that you can still mint when it's deactivated, and #191 is about the rounding feature itself