First Flight #15: Mondrian Wallet

Summary

Mondrian Wallet states that the tokenURI should maintain equal distribution. The source code indicates 7 out of 10 times, the Mondrian art painting selected would be ART_FOUR.

Vulnerability Details

The probability of getting ART_FOUR is bigger than getting every other art piece. This is because %10 can have 9 values (0,1,2,3,4,5,6,7,8,9) , and the if statement, only gives the first three arts to values 0,1,2 respectively. All other possible values, 3,4,5,6,7,8,9 are given ART_FOUR

Impact

Low, as it does not impact the functioning of the wallet

Tools Used

Manual Review

Recommendations

Instead of using tokenId % 10;, it is recommended to use tokenId % 4;. This will create an equal distribution of the token Uri.
It is also worth mentioning that this is not a randomized source, as anyone can wait and listen to the blockchain to get a specific Mondrian art painting. Implementing an Oracle could provide a real random source.