First Flight #2: Puppy Raffle

Summary

The use of weak source of randomness in the PuppyRaffle::selectWinner function leads to precomputable results.

Vulnerability Details

Anyone has access to the variables used to calculate the PuppyRaffle::winnerIndex and the PuppyRaffle::rarity variables. So anyone can precompute those results and participate only if they are going to win. The exploitability of this function is increased due to the functionality of the PuppyRaffle::refund function which allows participants to be dropped from the raffle without modifying the length of the PuppyRaffle::players array.

When calculating PuppyRaffle::winnerIndex, block.timestamp is used, this variable is a bit more tricky to use to exploit the vulnerability but it is not a problem at all.

Impact

The raffle can always be manipulated

Tools Used

Foundry

Recommendations

Chainlink's oracle can be used in order to prevent this