First Flight #2: Puppy Raffle

Summary

'refund' function introduces duplicates in players array

Vulnerability Details

The refund function gives option of the function callers to exit the raffle retrieving back 'entranceFee' amount of money. Where this does not result in a reentrancy attack(reported in another finding) leaves the corresponding index in players array with value address(0).

Impact

If the refund is called twice for different indexes we would end up with players array having duplicate values (address(0)). That would make it impossible for further addresses to enter the raffle given the implementation of the 'enterRaffle' function which reverts if duplicate addresses are found in the players array.

Tools Used

Manual review

Recommendations

Remove the refund() function.