MyCut

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

Claimants receive reduced Rewards due to incorrect distribution calculation

When calculating additional rewards distribution for claimers who claimed on time it is being used as denominator the length of the players array instead the claimants' length.

Description

  • Normal behavior - Manager closes the pot and if there are remaining rewards they should be calculated properly and distributed to the eligible claimers

  • Issue - Since the calculation is wrong using the players array's length, those additional rewards can be heavily reduced especially if the players are a lot and the user who claimed on time are not that many.

@> uint256 claimantCut = (remainingRewards - managerCut) / i_players.length;

Risk

Likelihood:

  • Likelihood is high: this can happen anytime when a pot has a lot of players and not all of them has claimed on time

Impact:

  • Impact is high: Users who fairly claimed on time and must receive additional rewards will receive less than expected.

Proof of Concept

  1. Owner creates a contests with 10 players and total rewards of 500 tokens.

  2. 6 of the players claim on time

  3. Deadline period passes and owner closes the pot

  4. Each of these players must receive 30 tokens additionaly -> remaining rewards = 500 - 6 * 50 = 200. 200 - managerCut = 200 - 20 = 180. And 180 / claimers = 180 / 6 = 30. However, they will receive almost half of that because of the issue in distribution

function test_claimantsReceiveLessRewards() public mintAndApproveTokens {
address[] memory addresses = new address[](10);
uint256[] memory nums = new uint256[](10);
for (uint256 i = 0; i < 10; i++) {
addresses[i] = address(uint160(i + 1));
nums[i] = 50;
}
vm.startPrank(user);
contest = ContestManager(conMan).createContest(addresses, nums, IERC20(ERC20Mock(weth)), 500);
ContestManager(conMan).fundContest(0);
vm.stopPrank();
assertEq(0, ERC20Mock(weth).balanceOf(conMan));
assertEq(500, ERC20Mock(weth).balanceOf(contest));
for (uint256 i = 0; i < 6; i++) {
vm.prank(addresses[i]);
Pot(contest).claimCut();
}
assertEq(200, Pot(contest).getRemainingRewards());
assertEq(50, ERC20Mock(weth).balanceOf(addresses[0]));
vm.warp(91 days);
vm.prank(user);
ContestManager(conMan).closeContest(contest);
// with the current set up, players claimers and rewards each individual who claimed must now receive after closeContest additional 30 tokens
// but it will not because in the reward distribution it is used players.length instead claimants.len
assertNotEq(80, ERC20Mock(weth).balanceOf(addresses[0]));
// balanceBefore 50 + expected rewards(30) = 80, but this is not the balance of the claimer
assertEq(68, ERC20Mock(weth).balanceOf(addresses[0]));
// claimer received 18 more rewards instead of 30
}

Recommended Mitigation

Fix the issue by using the correct array length

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