Puppy Raffle
AI First Flight #1
Beginner FriendlyFoundrySolidityNFT
EXP
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Submission Details
Severity: high
Valid

Relying on the players array length creates DoS on some functions

oruzix

By calling the refund function, users accidentally create a permanent DoS on the withdrawFees function

Description

  • Due to the selectWinner function calculating prize and fee amounts based on the length of the players array, which doesn't change upon refund, calling the refund function creates a permanent DoS of withdrawFees since it creates a mismatch of the totalFees variable and the ETH balance of the contract, which is enforced in the require statement in the withdrawFees.

uint256 winnerIndex =
uint256(keccak256(abi.encodePacked(msg.sender, block.timestamp, block.difficulty))) % players.length;
​
address winner = players[winnerIndex];
require(address(this).balance == uint256(totalFees), "PuppyRaffle: There are currently players active!");

  • A more extreme case is if more than 20% of users in the raffle (could also be only one refund with a total of 4 users in the raffle) call the refund function, which will result in DoS of the selectWinner function, and therefore also withdrawFees, since there will be insufficient balance for sending prize ETH to the winner address.

    uint256 totalAmountCollected = players.length * entranceFee;
    uint256 prizePool = (totalAmountCollected * 80) / 100;
    uint256 fee = (totalAmountCollected * 20) / 100;
    totalFees = totalFees + uint64(fee);
    //...
    (bool success,) = winner.call{value: prizePool}("");
    require(success, "PuppyRaffle: Failed to send prize pool to winner");

Recommended Mitigation

  • Don't rely on the length of the players array in the selectWinner function, have seperate variable which will track how many players are in the raffle.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 7 hours ago
Submission Judgement Published
Validated
Assigned finding tags:

[H-04] `PuppyRaffle::refund` replaces an index with address(0) which can cause the function `PuppyRaffle::selectWinner` to always revert

## Description `PuppyRaffle::refund` is supposed to refund a player and remove him from the current players. But instead, it replaces his index value with address(0) which is considered a valid value by solidity. This can cause a lot issues because the players array length is unchanged and address(0) is now considered a player. ## Vulnerability Details ```javascript players[playerIndex] = address(0); @> uint256 totalAmountCollected = players.length * entranceFee; (bool success,) = winner.call{value: prizePool}(""); require(success, "PuppyRaffle: Failed to send prize pool to winner"); _safeMint(winner, tokenId); ``` If a player refunds his position, the function `PuppyRaffle::selectWinner` will always revert. Because more than likely the following call will not work because the `prizePool` is based on a amount calculated by considering that that no player has refunded his position and exit the lottery. And it will try to send more tokens that what the contract has : ```javascript uint256 totalAmountCollected = players.length * entranceFee; uint256 prizePool = (totalAmountCollected * 80) / 100; (bool success,) = winner.call{value: prizePool}(""); require(success, "PuppyRaffle: Failed to send prize pool to winner"); ``` However, even if this calls passes for some reason (maby there are more native tokens that what the players have sent or because of the 80% ...). The call will thankfully still fail because of the following line is minting to the zero address is not allowed. ```javascript _safeMint(winner, tokenId); ``` ## Impact The lottery is stoped, any call to the function `PuppyRaffle::selectWinner`will revert. There is no actual loss of funds for users as they can always refund and get their tokens back. However, the protocol is shut down and will lose all it's customers. A core functionality is exposed. Impact is high ### Proof of concept To execute this test : forge test --mt testWinnerSelectionRevertsAfterExit -vvvv ```javascript function testWinnerSelectionRevertsAfterExit() public playersEntered { vm.warp(block.timestamp + duration + 1); vm.roll(block.number + 1); // There are four winners. Winner is last slot vm.prank(playerFour); puppyRaffle.refund(3); // reverts because out of Funds vm.expectRevert(); puppyRaffle.selectWinner(); vm.deal(address(puppyRaffle), 10 ether); vm.expectRevert("ERC721: mint to the zero address"); puppyRaffle.selectWinner(); } ``` ## Recommendations Delete the player index that has refunded. ```diff - players[playerIndex] = address(0); + players[playerIndex] = players[players.length - 1]; + players.pop() ```

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