First Flight #2: Puppy Raffle

Summary

The refund function is vulnerable to reentrancy attacks, as it can invoke the sendValue function multiple times.

Vulnerability Details

The refund function does not adhere to the checks-effects-interactions pattern, which could allow an attacker to steal funds from the contract.

Impact

This vulnerability allows anyone to create a malicious smart contract that can invoke the refund function multiple times using the fallback or receive functions. Because the refund function doesn't follow the checks-effects-interactions pattern, the contract can send the entranceFee multiple times without changing the state of players[playerIndex] to address(0).

Tools Used

Manual Review

Recommendations

1. To fix the bug and ensure the function follows the checks-effects-interactions pattern, move the line players[playerIndex] = address(0); before the line payable(msg.sender).sendValue(entranceFee);.

2. Implement the use of ReentrancyGuard.sol and apply the nonReentrant modifier to protect the function from reentrancy attacks.