MyCut

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

closePot() splits the leftover rewards by the total number of players instead of the number of claimants — claimants are underpaid and the difference is stranded

Root + Impact

Description

When a Pot is closed after 90 days, the leftover (unclaimed) rewards are split among the players who already claimed (claimants) — but the code divides by i_players.length (everyone, including players who never claimed):

@> uint256 managerCut = remainingRewards / managerCutPercent;
@> i_token.transfer(msg.sender, managerCut);
@>
@> uint256 claimantCut = (remainingRewards - managerCut) / i_players.length;
@> for (uint256 i = 0; i < claimants.length; i++) {
@> _transferReward(claimants[i], claimantCut);
@> }

Each claimant therefore receives less than their fair share, and the difference stays locked in the Pot forever (nothing ever sends the leftover out). With 3 players where only 2 claimed, the leftover is divided by 3 instead of 2, so each claimant gets 3 instead of 4.5 and 3 ether is stranded.

Risk

Likelihood: Medium — it triggers whenever a Pot is closed with at least one player who never claimed, which is the normal case for unclaimed rewards.

Impact: High — claimants are systematically underpaid on every close with unclaimed players, and the shortfall is permanently locked in the Pot.

Proof of Concept

Three players (Alice 60, Bob 30, Carol 10). Alice and Bob claim; Carol never does. After 91 days the Pot is closed: the leftover is 10, the manager takes 1, and the remaining 9 is split by 3 (all players) instead of 2 (claimants), so Alice and Bob get 3 each instead of 4.5, and 3 ether is stranded.

function test_M1_closePotDividesByAllPlayersNotClaimants() public {
_createAndFundContest();
​
// Alice and Bob claim; Carol never does.
vm.prank(alice);
Pot(contest).claimCut();
vm.prank(bob);
Pot(contest).claimCut();
​
assertEq(Pot(contest).getRemainingRewards(), 10 ether, "only Carol's 10 is left");
​
uint256 aliceBefore = weth.balanceOf(alice);
uint256 bobBefore = weth.balanceOf(bob);
​
vm.warp(91 days);
vm.prank(owner);
manager.closeContest(contest);
​
// Leftover = 10. Manager cut = 10 / 10 = 1. Remainder = 9.
// Correct split among the 2 claimants: 9 / 2 = 4.5 each.
// Buggy split among all 3 players: 9 / 3 = 3 each.
uint256 aliceCut = weth.balanceOf(alice) - aliceBefore;
uint256 bobCut = weth.balanceOf(bob) - bobBefore;
assertEq(aliceCut, 3 ether, "alice got 3 (divided by 3 players)");
assertEq(bobCut, 3 ether, "bob got 3 (divided by 3 players)");
assertLt(aliceCut, 4.5 ether, "alice was underpaid vs the correct 4.5");
​
// 10 - 1 (manager) - 3 - 3 = 3 ether stuck in the Pot forever.
assertEq(weth.balanceOf(contest), 3 ether, "3 ether stranded in the Pot");
}

Recommended Mitigation

Divide by claimants.length (and guard against claimants.length == 0).

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

Lead Judging Commences

ai-first-flight-judge Lead Judge about 2 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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