TwentyOne

First Flight #29
Beginner FriendlyGameFiFoundrySolidity
100 EXP
View results
Submission Details
Severity: medium
Invalid

Insecure Ether Transfer Mechanism Using transfer in the endGame Function

Summary

The transfer function is used to send Ether to users at the end of the game. While transfer is a commonly used method for sending funds, it comes with certain limitations that can cause security issues, especially in contracts that interact with other contracts or users with complex logic.

Vulnerability Details

The vulnerability lies in the use of transfer to send Ether in the endGame function. Although transfer is simple and generally considered safe for sending small amounts of Ether, it has several issues that can cause failures:

  • Gas Limitation: transfer sends only 2300 gas to the receiving contract, which may be insufficient if the receiving contract performs complex operations or modifies its state.

  • Future Incompatibility: As the Ethereum Virtual Machine (EVM) evolves, the gas cost of certain operations may increase, causing 2300 gas to become insufficient in the future.

This means that if the receiving contract requires more gas to perform necessary operations, the transfer will fail.

function endGame(address player, bool playerWon) internal {
delete playersDeck[player].playersCards; // Clear the player's cards
delete dealersDeck[player].dealersCards; // Clear the dealer's cards
delete availableCards[player]; // Reset the deck
if (playerWon) {
payable(player).transfer(2 ether); // Transfer the prize to the player @audit- better use call
emit FeeWithdrawn(player, 2 ether); // Emit the prize withdrawal event
}
}

Impact

  • Funds indirectly at risk: If the receiving contract requires more gas to execute its logic, the transfer will fail, potentially leaving funds trapped in the contract and not properly transferred to the player.

  • Disruption in functionality: This issue could cause a disruption in the functionality of the system, especially if the contract is integrated with other contracts that need to perform complex operations when receiving Ether.

  • Scalability and sustainability: As the EVM evolves, this issue could become more critical, as the gas required for certain operations may increase, exacerbating failures when using transfer.

Tools Used

Manual Review

Recommendations

To mitigate this issue, it is recommended to replace transfer with call, which allows for more flexibility by passing all available gas to the receiving contract. This ensures that the receiving contract can execute its logic without being restricted by the 2300 gas limit imposed by transfer. Additionally, using call is considered a more future-proof solution, as it provides greater compatibility with evolving gas costs.

Updates

Lead Judging Commences

inallhonesty Lead Judge 7 months ago
Submission Judgement Published
Invalidated
Reason: Non-acceptable severity

Support

FAQs

Can't find an answer? Chat with us on Discord, Twitter or Linkedin.