MyCut

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

`Pot.closePot` divides bonus by `i_players.length` instead of `claimants.length`, underpaying every claimant and permanently locking residual funds in the Pot

Root + Impact

Description

  • After the 90-day window, Pot.closePot is meant to take a 10% manager cut and distribute the remainder equally among those who claimed in time (per the README: "the remainder is distributed equally to those who claimed in time").

  • The implementation computes claimantCut by dividing by i_players.length (every original player), not claimants.length (those who actually claimed). Each claimant therefore receives a fraction claimants.length / i_players.length of what they were promised, and the rest of the bonus pool stays locked in the Pot forever.

// src/Pot.sol :: closePot
if (remainingRewards > 0) {
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);
}
}

Risk

Likelihood:

  • Triggered whenever at least one configured player does not claim during the 90-day window — i.e. the exact scenario closePot was built to handle.

  • No attacker required; this is the protocol's normal happy-path on any non-fully-claimed Pot.
    Impact:

  • Claimants receive fewer tokens than promised. With 3 of 5 players claiming, each gets 1800 / 5 = 360 instead of 1800 / 3 = 600 — a 40% shortfall.

  • Residual funds (720 tokens in the 5-player / 1000-each / 3-claimants example) are permanently locked in the Pot. No function exists to recover them.

Proof of Concept

function test_claimantCutUnderpaysAndLocksFunds() public {
Pot pot = _setupPot5Players1000Each();
vm.prank(alice); pot.claimCut();
vm.prank(bob); pot.claimCut();
vm.prank(carol); pot.claimCut();
vm.warp(block.timestamp + 91 days);
vm.prank(owner);
manager.closeContest(address(pot));
// Each claimant's bonus should be (2000 - 200) / 3 = 600.
// Actual code gives (2000 - 200) / 5 = 360.
uint256 aliceBonus = token.balanceOf(alice) - 1000e18;
assertEq(aliceBonus, 360e18); // PASSES — proves the bug
// 720 tokens stuck in the Pot with no recovery path.
assertEq(token.balanceOf(address(pot)), 720e18);
}

Run with forge test --match-test test_claimantCutUnderpaysAndLocksFunds -vvv. Test passes; assertions show underpayment and locked residue.

Recommended Mitigation

Divide by the number of actual claimants. Add a guard for zero claimants to avoid division-by-zero (in that case the bonus pool should remain with the manager or have an explicit recovery path).

if (remainingRewards > 0) {
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);
- }
+ uint256 bonusPool = remainingRewards - managerCut;
+ if (claimants.length > 0) {
+ uint256 claimantCut = bonusPool / claimants.length;
+ for (uint256 i = 0; i < claimants.length; i++) {
+ _transferReward(claimants[i], claimantCut);
+ }
+ } else {
+ // No one claimed — explicit decision: send remainder to manager
+ i_token.transfer(msg.sender, bonusPool);
+ }
+ remainingRewards = 0;
}
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 17 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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