MyCut

AI First Flight #8
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EXP
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Submission Details
Severity: high
Valid

`closePot()` Under-Distributes Rewards by Dividing by Total Players but Paying Only Claimants

closePot() Under-Distributes Rewards by Dividing by Total Players but Paying Only Claimants

Description

In closePot(), the post-deadline claimant allocation is computed using the total number of registered players (i_players.length), but the transfer loop pays only addresses in claimants.

uint256 claimantCut = (remainingRewards - managerCut) / i_players.length;
for (uint256 i = 0; i < claimants.length; i++) {
_transferReward(claimants[i], claimantCut);
}

This mismatch causes systematic under-distribution whenever claimants.length < i_players.length. The protocol intends to distribute the post-cut remainder equally among those who claimed in time, but the current formula reduces each claimant’s share and leaves excess tokens in the pot.

As a result, the settlement outcome diverges from the protocol’s stated economic model and a non-trivial residual balance remains in the contest contract.


Risk

Likelihood: High

This behavior is deterministic in normal operation whenever not all players claim before closure, which is a common case in real contests.

Impact: Medium

Claimants receive less than intended and contest funds remain trapped in the pot after closure, creating predictable economic inefficiency and payout unfairness.


Proof of Concept

The behavior is demonstrated by the following PoC test:

function testClosePot_UnderDistributes_WhenFewClaimantsAndManyPlayers() public {
address[] memory players = new address[](3);
players[0] = p1;
players[1] = p2;
players[2] = p3;
uint256[] memory rewards = new uint256[](3);
rewards[0] = 40;
rewards[1] = 30;
rewards[2] = 30;
(address contest, Pot pot) = _createAndFund(players, rewards, 100);
vm.prank(p1);
pot.claimCut(); // remainingRewards = 60, claimants.length = 1
uint256 managerBefore = token.balanceOf(address(manager));
uint256 p1Before = token.balanceOf(p1);
_close(contest);
uint256 managerAfter = token.balanceOf(address(manager));
uint256 p1After = token.balanceOf(p1);
// managerCut = 60 / 10 = 6
// claimantCut = (60 - 6) / 3 = 18; only one claimant is paid
assertEq(managerAfter - managerBefore, 6);
assertEq(p1After - p1Before, 18);
assertEq(token.balanceOf(contest), 36);
assertEq(pot.getRemainingRewards(), 60);
}

Run:

forge test --match-test testClosePot_UnderDistributes_WhenFewClaimantsAndManyPlayers -vv

Output:

[PASS] testClosePot_UnderDistributes_WhenFewClaimantsAndManyPlayers() (gas: 1122444)
Suite result: ok. 1 passed; 0 failed; 0 skipped; finished in 2.22ms (665.34µs CPU time)
Ran 1 test suite in 20.78ms (2.22ms CPU time): 1 tests passed, 0 failed, 0 skipped (1 total tests)

The test shows that with one claimant and three players, only 18 is paid to the claimant while 36 remains in the pot, proving under-distribution caused by the denominator mismatch.


Recommended Mitigation

Align the denominator with the actual payout set.

- uint256 claimantCut = (remainingRewards - managerCut) / i_players.length;
+ uint256 claimantCut = (remainingRewards - managerCut) / claimants.length;

Also add an explicit handling path for integer-division dust and zero-claimant scenarios so closure behavior is well-defined and final.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 3 hours ago
Submission Judgement Published
Validated
Assigned finding tags:

[H-02] Incorrect logic in `Pot::closePot` leads to unfair distribution to `claimants`, potentially locking the funds with no way to take that out

## Description in `closePot` function while calclulating the shares for claimaint cut, `i_players.length` is used, instead of `claimants.length`, causing low amount being distributed to claimants. ## Vulnerability Details [2024-08-MyCut/src/Pot.sol at main · Cyfrin/2024-08-MyCut (github.com)](https://github.com/Cyfrin/2024-08-MyCut/blob/main/src/Pot.sol#L57) `Pot::closePot` function is meant to be called once contest passed 90 days, it sends the owner cut to owner and rest is splitted among the users who claimed b/w 90 days period. However, current implementation is wrong.&#x20; It uses total users (i_players.length) instead of the users (claimants.length) who claimed during the duration. This creates an unfair distribution to the participants and some of the funds could be locked in the contract. In worst case scenerio, it could be 90% if nobody has claimed from the protocol during the 90 days duration. ## POC In existing test suite, add following test: ```solidity function testUnfairDistributionInClosePot() public mintAndApproveTokens { // Setup address[] memory testPlayers = new address[](3); testPlayers[0] = makeAddr("player1"); testPlayers[1] = makeAddr("player2"); testPlayers[2] = makeAddr("player3"); uint256[] memory testRewards = new uint256[](3); testRewards[0] = 400; testRewards[1] = 300; testRewards[2] = 300; uint256 testTotalRewards = 1000; // Create and fund the contest vm.startPrank(user); address testContest = ContestManager(conMan).createContest( testPlayers, testRewards, IERC20(ERC20Mock(weth)), testTotalRewards ); ContestManager(conMan).fundContest(0); vm.stopPrank(); // Only player1 claims their reward vm.prank(testPlayers[0]); Pot(testContest).claimCut(); // Fast forward 91 days vm.warp(block.timestamp + 91 days); // Record balances before closing the pot uint256 player1BalanceBefore = ERC20Mock(weth).balanceOf( testPlayers[0] ); // Close the contest vm.prank(user); ContestManager(conMan).closeContest(testContest); // Check balances after closing the pot uint256 player1BalanceAfter = ERC20Mock(weth).balanceOf(testPlayers[0]); // Calculate expected distributions uint256 remainingRewards = 600; // 300 + 300 unclaimed rewards uint256 ownerCut = remainingRewards / 10; // 10% of remaining rewards uint256 distributionPerPlayer = (remainingRewards - ownerCut) / 1; // as only 1 user claimed uint256 fundStucked = ERC20Mock(weth).balanceOf(address(testContest)); // actual results console.log("expected reward:", distributionPerPlayer); console.log( "actual reward:", player1BalanceAfter - player1BalanceBefore ); console.log("Fund stucked:", fundStucked); } ``` then run `forge test --mt testUnfairDistributionInClosePot -vv` in the terminal and it will show following output: ```js [⠊] Compiling... [⠒] Compiling 1 files with Solc 0.8.20 [⠘] Solc 0.8.20 finished in 1.63s Compiler run successful! Ran 1 test for test/TestMyCut.t.sol:TestMyCut [PASS] testUnfairDistributionInClosePot() (gas: 905951) Logs: User Address: 0x6CA6d1e2D5347Bfab1d91e883F1915560e09129D Contest Manager Address 1: 0x7BD1119CEC127eeCDBa5DCA7d1Bd59986f6d7353 Minting tokens to: 0x6CA6d1e2D5347Bfab1d91e883F1915560e09129D Approved tokens to: 0x7BD1119CEC127eeCDBa5DCA7d1Bd59986f6d7353 expected reward: 540 actual reward: 180 Fund stucked: 360 Suite result: ok. 1 passed; 0 failed; 0 skipped; finished in 1.58ms (506.33µs CPU time) ``` ## Impact Loss of funds, Unfair distribution b/w users ## Recommendations Fix the functions as shown below: ```diff function closePot() external onlyOwner { if (block.timestamp - i_deployedAt < 90 days) { revert Pot__StillOpenForClaim(); } if (remainingRewards > 0) { uint256 managerCut = remainingRewards / managerCutPercent; i_token.transfer(msg.sender, managerCut); - uint256 claimantCut = (remainingRewards - managerCut) / i_players.length; + uint256 totalClaimants = claimants.length; + if(totalClaimant == 0){ + _transferReward(msg.sender, remainingRewards - managerCut); + } else { + uint256 claimantCut = (remainingRewards - managerCut) / claimants.length; for (uint256 i = 0; i < claimants.length; i++) { _transferReward(claimants[i], claimantCut); } } + } } ```

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