MyCut

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

closePot() divides leftover rewards by total players instead of claimants, locking funds permanently

Root + Impact

Description

When a pot is closed, the leftover (unclaimed) rewards are meant to be distributed among the players who actually claimed (the claimants), after taking the manager's cut. The full leftover should be paid out so nothing is stranded. The problem is that closePot() computes each claimant's share by dividing by i_players.length (ALL players) but only loops over claimants (those who actually claimed). When fewer players claimed than the total, only a fraction of the leftover is distributed and the remainder is permanently locked in the contract.

function closePot() external onlyOwner {
...
if (remainingRewards > 0) {
uint256 managerCut = remainingRewards / managerCutPercent;
i_token.transfer(msg.sender, managerCut);
// @> divides by i_players.length (all), but loop pays only claimants
uint256 claimantCut = (remainingRewards - managerCut) / i_players.length;
for (uint256 i = 0; i < claimants.length; i++) {
_transferReward(claimants[i], claimantCut);
}
}
}

Risk

Likelihood:

  • Occurs whenever closePot is called and the number of claimants is less than the total number of players — the normal case, since some players never claim.

Impact:

  • Only (claimants.length / i_players.length) of the post-cut leftover is distributed; the rest is permanently stuck in the contract with no way to recover it.

  • Example: 10 players, 700 leftover, 3 claimants -> managerCut 70, claimantCut = 630/10 = 63 each -> 189 paid, 441 tokens (63%) locked forever.

Proof of Concept

With 10 players, remainingRewards = 700, and 3 claimants:

  • managerCut = 700 / 10 = 70

  • claimantCut = (700 - 70) / 10 = 63

  • distributed = 70 + (63 * 3) = 259

  • locked = 700 - 259 = 441 tokens stranded in the contract

function test_PoC_LockedFundsWrongDivisor() public {
// Setup: 10 players, total 1000 tokens. Only 3 claim their rewards.
// After the 3 claims, remainingRewards = 700 (the 7 who didn't claim).
// Fast-forward past the 90-day claim window
vm.warp(block.timestamp + 90 days + 1);
uint256 potBalanceBefore = token.balanceOf(address(pot));
// Owner closes the pot
vm.prank(owner);
contestManager.closeContest(address(pot));
// Accounting of what SHOULD vs DID get distributed:
// managerCut = 700 / 10 = 70
// claimantCut = (700 - 70) / 10 = 63 (BUG: divides by i_players.length = 10)
// distributed = 70 + 63 * 3 = 259
// locked = 700 - 259 = 441
uint256 potBalanceAfter = token.balanceOf(address(pot));
// 441 tokens remain stuck in the pot forever
assertEq(potBalanceAfter, potBalanceBefore - 259);
assertGt(potBalanceAfter, 0); // funds locked, non-zero leftover trapped
}

Recommended Mitigation

Divide by claimants.length so the entire post-cut leftover is distributed among the actual claimants. Guard against claimants.length == 0 (skip the distribution or send the remainder to the manager) to avoid division by zero.

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