unforgiven - attacker can force pause the Auctions

[sherlock-admin]

unforgiven

high

attacker can force pause the Auctions

Summary

function _createAuction() is called after old auctions is settled. the issue is that code tires to mint new token by calling token.mint() and if that call reverts then code pauses the Auction. attacker can send low gas amount in the call and make the call to mint revert because of OOG and then Auction contract will pause the auction operations.

if Auction is paused then tokens won't be minted and Founders won't receive their vesting allocations. for example if a founders vesting time was for 1 week and auction time was for 1 day, then that founder expect to receive 7 NFT tokens in his vesting time, but attacker can cause force pause between auctions and make the funder to receive less NFT, also the pause will block the core functionality of the Auction, so I believe this is a High issue.

Vulnerability Detail

This _createAuction() code, as you can see if token.mint() reverts, then auction will be paused.

    /// @dev Creates an auction for the next token
    function _createAuction() private returns (bool) {
        // Get the next token available for bidding
        try token.mint() returns (uint256 tokenId) {
            // Store the token id
            auction.tokenId = tokenId;
..........
..........
..........
        } catch {
            // Pause the contract if token minting failed
            _pause();
            return false;
        }

because code pauses the auction even if the call reverted because of the OOG, so attacker can send low gas and cause OOG in the mint execution and pause the Auction. This is the POC:

1. let's assume the Token.mint() need 30K gas.
2. let's assume settleCurrentAndCreateNewAuction() execution until Token.mint() line requires 100K gas.
3. when an auction is finished attacker would frontrun others and would call settleCurrentAndCreateNewAuction() with 120K gas.
4. function settleCurrentAndCreateNewAuction() will run until Token.mint() and it would send less than 20K gas to the mint function.
5. mint call will revert and the catch part will be executed and would pause the Auction to pause.
6. attacker was able to pause the Auction while pausing is only for Founder level access or incase of the Token contract doesn't allow minting.

because founders receive their vesting tokens based on expire time so it's essential that auctions are executed and tokens are minted so they receive their token. if auction is paused then founders will receive less tokens.

Impact

attacker can manipulate Auction mechanism and pause the auction.

Code Snippet

https://github.com/sherlock-audit/2023-09-nounsbuilder/blob/db232c649b425c36f5a93607c95cfdf0e5962b2f/nouns-protocol/src/auction/Auction.sol#L292-L330

Tool used

Manual Review

Recommendation

make sure there is enough gas left when calling mint() function or doesn't pause when call revered with no error.

Duplicate of #243