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

`Pot::closePot` divides the leftover by all registered players instead of the actual claimants, underpaying claimants and locking the rest of the pool forever

summus

Root + Impact

Description

  • After 90 days the manager closes the Pot. The README says the manager takes a cut of the remaining pool and "the remainder is distributed equally to those who claimed in time".

  • However, closePot divides the remainder by i_players.length (every registered player) but loops only over claimants. Every player who did not claim shrinks everyone's share, and the undistributed part stays in the Pot, which has no way to withdraw it.

function closePot() external onlyOwner {
...
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);
}
}
}

With k claimants out of N players, (remainingRewards - managerCut) * (N - k) / N tokens, plus rounding dust, remain in the Pot after closing.

Risk

Likelihood:

  • Every time at least one player does not claim within 90 days. This is exactly the case closePot exists for: When every player claimed, remainingRewards would be 0 and the branch would never run.

    The fewer players claim, the larger the error. It is deterministic and needs no special input.

Impact:

  • Claimants who claimed in time get only k / N of the bonus they are entitled to.

  • The remainder is locked in the Pot permanently. Pot has no sweep or withdraw function, and ContestManager cannot move the Pot's tokens.

Proof of Concept

Four players have 100 tokens each and only player1 claims. After closing, player1 should receive the whole 270 bonus (300 - 30 manager cut) but gets 67. 203 tokens stay stuck in the Pot.

function testClaimantCutDividedByAllPlayers() public {
ERC20Mock token = new ERC20Mock("W", "W", admin, 0);
token.mint(admin, 400);
address[] memory players = new address[](4);
players[0] = player1; players[1] = player2; players[2] = player3; players[3] = player4;
uint256[] memory rewards = new uint256[](4);
rewards[0] = 100; rewards[1] = 100; rewards[2] = 100; rewards[3] = 100;
​
vm.startPrank(admin);
token.approve(address(conMan), 400);
Pot pot = Pot(conMan.createContest(players, rewards, IERC20(address(token)), 400));
conMan.fundContest(0);
vm.stopPrank();
​
vm.prank(player1);
pot.claimCut(); // only player1 claims in time
​
vm.warp(block.timestamp + 90 days);
vm.prank(admin);
conMan.closeContest(address(pot));
​
assertEq(token.balanceOf(player1), 100 + 67); // should be 100 + 270
assertEq(token.balanceOf(address(pot)), 203); // stuck forever
}

Recommended Mitigation

Divide by the number of claimants, and send the rounding dust (or everything, when nobody claimed) to the manager so that nothing is left behind.

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 toDistribute = remainingRewards - managerCut;
+ if (claimants.length > 0) {
+ uint256 claimantCut = toDistribute / claimants.length;
+ for (uint256 i = 0; i < claimants.length; i++) {
+ _transferReward(claimants[i], claimantCut);
+ }
+ managerCut += toDistribute - claimantCut * claimants.length; // dust
+ } else {
+ managerCut += toDistribute;
+ }
+ remainingRewards = 0;
+ i_token.transfer(msg.sender, managerCut);
}
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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