MyCut

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

[H-1] `closePot` uses the wrong divisor, locking most of the remainder

Root + Impact

Description

  • When a Pot is closed, the unclaimed rewards (minus the manager cut) are supposed to be split equally among the players who claimed in time. closePot instead divides by i_players.length (every whitelisted player, including those who never claimed). Each on-time claimant therefore receives too little, and the undistributed shortfall is stuck in the Pot with no function able to withdraw it.

src/Pot.sol:53-61
if (remainingRewards > 0) {
uint256 managerCut = remainingRewards / managerCutPercent;
i_token.transfer(msg.sender, managerCut);
uint256 claimantCut = (remainingRewards - managerCut) / i_players.length; // BUG: should be claimants.length
for (uint256 i = 0; i < claimants.length; i++) {
_transferReward(claimants[i], claimantCut);
}
}

Risk

Likelihood:

  • High (happens on every close where claimants.length != i_players.length, i.e. almost always).

Impact:

  • High (permanent fund lock)

  • Permanent loss of user funds. The fewer players that claim in time, the larger the locked amount (with 1 of N claimants, roughly (N-1)/N of the distributable remainder is lost). No privileged or unprivileged action can recover it.

Proof of Concept

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;
import {Test, console} from "lib/forge-std/src/Test.sol";
import {ContestManager} from "../src/ContestManager.sol";
import {Pot} from "../src/Pot.sol";
import {IERC20} from "lib/openzeppelin-contracts/contracts/token/ERC20/ERC20.sol";
import {ERC20Mock} from "./ERC20Mock.sol";
// H-1: Pot.closePot divides the leftover among ALL whitelisted players
// (i_players.length) instead of only those who claimed in time
// (claimants.length). The shortfall is never sent to anyone and is
// permanently locked in the Pot.
contract PoC_LockedFunds is Test {
ContestManager conMan;
ERC20Mock weth;
address user = makeAddr("user"); // owner / manager
address player1 = makeAddr("player1");
address player2 = makeAddr("player2");
address[] players = [player1, player2];
uint256[] rewards = [500, 500];
uint256 totalRewards = 1000;
address contest;
function setUp() public {
vm.startPrank(user);
conMan = new ContestManager();
weth = new ERC20Mock("WETH", "WETH", user, 0);
weth.mint(user, 1000 ether);
weth.approve(address(conMan), type(uint256).max);
contest = conMan.createContest(players, rewards, IERC20(weth), totalRewards);
conMan.fundContest(0);
vm.stopPrank();
}
function test_leftover_is_permanently_locked() public {
// Only player1 claims in time (gets 500). player2 never claims,
// so 500 should be split among the claimants (only player1).
vm.prank(player1);
Pot(contest).claimCut();
vm.warp(91 days);
vm.prank(user);
conMan.closeContest(contest);
// remaining = 500. managerCut = 500/10 = 50.
// claimantCut = (500-50)/i_players.length = 450/2 = 225 (WRONG divisor)
// correct would be /claimants.length = 450/1 = 450
// player1 therefore receives 225 instead of 450.
// 225 tokens stay stuck in the Pot with no way to withdraw them.
uint256 stuck = weth.balanceOf(contest);
assertEq(stuck, 225, "funds permanently locked in Pot");
console.log("Locked in Pot forever:", stuck);
}
}

Recommended Mitigation

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

Lead Judging Commences

ai-first-flight-judge Lead Judge about 7 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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