MyCut

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

Incorrect Bonus Distribution Divisor

Root + Impact

Description

  • Describe the normal behavior in one or more sentences


    Per the project README:

    After 90 days, the manager takes a cut of the remaining unclaimed pool, and the remainder is distributed equally to those who claimed in time.

    This implies the following formula:

    • remainingRewards represents unclaimed rewards

    • 10% goes to manager

    • 90% is distributed equally among claimants

Thus: bonusPerClaimant = (remainingRewards - managerCut) / claimants.length

  • Explain the specific issue or problem in one or more sentences


    The contract divides the bonus pool by the total number of players (i_players.length) instead of the number of claimants (claimants.length).


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

This creates a structural accounting mismatch:

  • Bonus is calculated assuming distribution to all players

  • Bonus is actually distributed only to claimants

As a result:

  • Claimants receive less than intended

  • A portion of bonus pool remains permanently locked in the contract

  • The contract behavior deviates from README specification

Risk

Likelihood:

  • This occurs whenever fewer than all players claim within 90 days.

  • This is a normal operational scenario under expected usage.

No abnormal input or malicious interaction is required.

Impact:

  • Tokens become permanently stuck in the contract.

  • The system violates its documented reward distribution logic.

  • Claimants are underpaid relative to protocol specification.

  • Financial outcomes differ from what users expect based on README.

This is a direct economic deviation from intended behavior.

Proof of Concept

Scenario:
Total players: 10
Claimants within 90 days: 3
Unclaimed pool (remainingRewards): 1000 tokens
### Current Implementation Behavior:
Manager cut:
1000 / 10 = 100
Bonus pool:
1000 - 100 = 900
Claimant cut (incorrect divisor):
900 / 10 = 90
Distributed:
3 × 90 = 270
Total distributed:
Manager: 100
Claimants: 270
Total: 370
Undistributed:
1000 - 370 = 630 tokens permanently locked
### Expected Behavior Per README
Claimant cut:
900 / 3 = 300
Distributed:
3 × 300 = 900
Total distributed:
Manager: 100
Claimants: 900
Total: 1000
No funds remain locked.

Recommended Mitigation

- uint256 claimantCut = (remainingRewards - managerCut) / i_players.length;
+ uint256 claimantCut = (remainingRewards - managerCut) / claimants.length;
Additionally, an explicit zero-claimant case should be handled to prevent division by zero and undefined bonus behavior:
+ if (claimants.length == 0) {
+ i_token.transfer(owner(), remainingRewards);
+ remainingRewards = 0;
+ return;
+ }
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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