Last Man Standing
First Flight #45
Beginner FriendlyFoundrySolidity
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Submission Details
Impact: medium
Likelihood: medium
Invalid

Withdrawal DoS if Winner is Reverting Contract

r4y4n3

Root + Impact

Description

  • Normal behavior:
    Winners should always be able to withdraw their winnings regardless of whether they are EOAs or smart contracts.

    Specific issue:
    The withdrawWinnings() function uses a low-level call to transfer ETH. If the recipient is a contract that reverts on ETH reception, the withdrawal fails permanently, locking the funds forever.

function withdrawWinnings() external nonReentrant {
uint256 amount = pendingWinnings[msg.sender];
require(amount > 0, "Game: No winnings to withdraw.");
​
(bool success, ) = payable(msg.sender).call{value: amount}(""); // @> Fails if recipient reverts
require(success, "Game: Failed to withdraw winnings.");
​
pendingWinnings[msg.sender] = 0;
emit WinningsWithdrawn(msg.sender, amount);
}

Risk

Likelihood:

  • Contracts without receive/fallback functions participate in the game.

  • Contracts with buggy or restrictive ETH reception logic become winners.

Impact:

  • Winner's funds are permanently locked with no recovery mechanism.

  • No way to force transfer the funds to the rightful winner.

  • Breaks the core game promise that winners can claim their prize.

Proof of Concept

contract RevertingContract {
function claimThrone(Game game) external payable {
game.claimThrone{value: msg.value}();
}
// No receive() or fallback() - will revert on ETH transfer
}
​
function testWithdrawalDoSRevertingContract() public {
// Reverting contract claims throne and becomes winner
revertingContract.claimThrone{value: INITIAL_CLAIM_FEE}(game);
vm.warp(block.timestamp + GRACE_PERIOD + 1);
game.declareWinner();
​
assertTrue(game.pendingWinnings(address(revertingContract)) > 0, "Should have winnings");
​
// Withdrawal fails permanently
vm.startPrank(address(revertingContract));
vm.expectRevert("Game: Failed to withdraw winnings.");
game.withdrawWinnings();
vm.stopPrank();
​
// Funds remain locked forever
assertTrue(game.pendingWinnings(address(revertingContract)) > 0, "Winnings still locked");
}

Recommended Mitigation

Implement a pull payment pattern with fallback mechanism or allow owner to recover stuck funds:

+ mapping(address => bool) public withdrawalFailed;
​
function withdrawWinnings() external nonReentrant {
uint256 amount = pendingWinnings[msg.sender];
require(amount > 0, "Game: No winnings to withdraw.");
​
(bool success, ) = payable(msg.sender).call{value: amount}("");
- require(success, "Game: Failed to withdraw winnings.");
- pendingWinnings[msg.sender] = 0;
+
+ if (success) {
+ pendingWinnings[msg.sender] = 0;
+ emit WinningsWithdrawn(msg.sender, amount);
+ } else {
+ withdrawalFailed[msg.sender] = true;
+ emit WithdrawalFailed(msg.sender, amount);
+ }
}
​
+ // Allow owner to recover funds for failed withdrawals
+ function recoverFailedWithdrawal(address winner, address newRecipient) external onlyOwner {
+ require(withdrawalFailed[winner], "No failed withdrawal");
+ uint256 amount = pendingWinnings[winner];
+ pendingWinnings[winner] = 0;
+ withdrawalFailed[winner] = false;
+ payable(newRecipient).transfer(amount);
+ }
Updates

Appeal created

inallhonesty Lead Judge 3 months ago
Submission Judgement Published
Invalidated
Reason: Non-acceptable severity
Assigned finding tags:

Doss by reverting contract / contract that doesn't implement receive.

The only party affected is the "attacker". Info at best.

r4y4n3 Submitter
3 months ago
inallhonesty Lead Judge
3 months ago
inallhonesty Lead Judge 3 months ago
Submission Judgement Published
Invalidated
Reason: Non-acceptable severity
Assigned finding tags:

Doss by reverting contract / contract that doesn't implement receive.

The only party affected is the "attacker". Info at best.

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