First Flight #2: Puppy Raffle

Summary

Missing overflow check in 'enterRaffle' function

Vulnerability Details

Solidity version of the contract is ^0.7.6 which means overflows happen quietly.

Impact

In theory it is possible the contract to be initialized with very high 'entranceFee' which would allow the function caller to engineer newPlayers array with appropriate length that causes "entranceFee * newPlayers.length" to overflow. This would allow the function caller to enter the raffle sending miniscule value.
Here is a test showcasing the scenarion:

1. Set the entrance fee to a very high value:
   uint256 entranceFee = type(uint256).max / 3 + 1;

2. Add this test and run it. It passes.:
   function testCanEnterRaffleExtreme() public {
   console.log("entranceFee: %s", entranceFee);
   address[] memory players = new address;
   players[0] = playerOne;
   players[1] = playerTwo;
   players[2] = playerThree;
   puppyRaffle.enterRaffle{value: 2}(players);
   assertEq(puppyRaffle.players(0), playerOne);
   }

I am setting the severity to medium as it is unlikely this scenario to happen.
There are far easier ways to render this contract unusable.

Tools Used

Manual review

Recommendations

Add overflow checks.