MyCut

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

closePot() divides remaining rewards by total players instead of claimants — unclaimed funds permanently lost

Root + Impact

Description

  • Normal behavior: After the 90-day claim window, closePot() should distribute remaining rewards equally among those who claimed in time.

  • The issue: claimantCut is calculated by dividing by i_players.length (total eligible players) but distributed by iterating over claimants (those who actually claimed). If fewer players claimed than total eligible, the division produces a smaller cut per claimant than available funds allow. The remainder is permanently locked in the contract with no recovery mechanism.

```solidity
// src/Pot.sol#56-59
uint256 managerCut = remainingRewards / managerCutPercent;
i_token.transfer(msg.sender, managerCut);
// @> divided by i_players.length (total) — should be claimants.length (actual)
uint256 claimantCut = (remainingRewards - managerCut) / i_players.length;
for (uint256 i = 0; i < claimants.length; i++) {
_transferReward(claimants[i], claimantCut);
}
```

Risk

Likelihood:

  • Any contest where fewer than 100% of eligible players claim triggers permanent fund loss — this is the expected common case.

  • The 90-day claim window exists precisely because not all players will claim — the bug triggers in every realistic deployment.

Impact:

  • Remaining funds after distribution are permanently locked — no withdrawal or recovery function exists in the contract.

  • With 10 players and 2 claimants, 80% of the redistributed pool is locked forever — significant fund loss at scale.

Proof of Concept

The following test demonstrates that when only 2 of 5 players claim, closePot() calculates claimantCut using the total player count (5) instead of the claimant count (2). The two claimants each receive 1/5 of the pool instead of 1/2, and the remaining 3/5 is permanently locked in the contract.

```solidity
function testWrongDivisorLocksRemainingFunds() public {
uint256 totalRewards = 1000e18;
address[] memory players = new address[](5);
uint256[] memory rewards = new uint256[](5);
for (uint256 i = 0; i < 5; i++) {
players[i] = address(uint160(i + 1));
rewards[i] = 200e18;
}
Pot pot = new Pot(players, rewards, token, totalRewards);
token.transfer(address(pot), totalRewards);
// Only 2 of 5 players claim
vm.prank(players[0]); pot.claimCut();
vm.prank(players[1]); pot.claimCut();
vm.warp(block.timestamp + 91 days);
pot.closePot();
uint256 lockedFunds = token.balanceOf(address(pot));
// Funds permanently locked — should be 0
assertGt(lockedFunds, 0);
}
```

Recommended Mitigation

Replace i_players.length with claimants.length in the claimantCut calculation. This ensures the remaining pool after the manager cut is divided equally among only those who actually claimed. Add a zero-claimant guard to prevent division by zero when no players claimed during the window.

```diff
function closePot() external onlyOwner {
if (block.timestamp - i_deployedAt < 90 days) revert Pot__StillOpenForClaim();
if (remainingRewards > 0) {
uint256 managerCut = remainingRewards / managerCutPercent;
i_token.safeTransfer(msg.sender, managerCut);
+ if (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 6 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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