First Flight #2: Puppy Raffle

Summary

The code provided for the enterRaffle function has a vulnerability related to overflow.

Vulnerability Details

The vulnerability arises from the line:

If the multiplication of entranceFee and newPlayers.length exceeds the maximum value that can be represented by a uint256 variable, an overflow will occur. Since all these parameters are manipulable by the sender, it is possible for the sender to enter a large number of addresses and a pre-calculated msg.value to bypass the check.

This vulnerability can be tested by setting up a large entranceFee amount (close to type(uint256).max) and sending an array with only two players, triggering an overflow.

Impact

If an attacker exploits this vulnerability by providing a large number of newPlayers addresses and a pre-calculated msg.value, they can enter the raffle without sending the required amount of funds and even reduce the fees.
Due to strict equality in withdrawFees, it will break this function and all actual and futures fees will be lost forever.

Tools Used

Manual review.

Recommendations

To mitigate this vulnerability, consider implementing the following measures:

1. Update to Solidity 0.8.0 or later versions, as these versions include a safe multiplication function, which prevents overflow issues.

2. Alternatively, you can use a safe multiplication function like safeMul from OpenZeppelin's SafeMath library to ensure that the multiplication does not result in an overflow.

3. Implement a limit on the number of addresses that can be passed in the newPlayers array to prevent potential abuse and reduce the risk of overflow.