First Flight #15: Mondrian Wallet

Description

The MondrainWallet is also an NFT and the protocol states:

You'll see the tokenURI function returns one of 4 random Mondrian art paintings. Each should have equal distribution and be random.

This invariant is broken due to the implementation of the MondrianWallet::tokenURI function.

• The random artwork is chosen based on: tokenId modulus 10 which is not random.

• The tokenId is user controlled and therefore the artwork for the NFT is predictable.

• The distribution is not equal as the result of modulus operation favours the ART_FOUR NFT.

Impact

Core invariant does not hold true and a user may be able to mint and choose whichever NFT artwork they like.

Recommended mitigation

• Use a purpose built, trusted and well-tested library for generating random numbers.

Tools Used

• Manual Review