This challenge predominantly utilizes Vyper version 0.4.0b4, which introduces the capability to import modules. In this case, it uses snekmate for the ERC721 standard implementation. To secure the flag, one must successfully remove the Art NFT from the Auction contract by winning the auction. The challenge, however, is the lack of tokens to place a winning bid.
Upon examining the deploy script, it's evident that the deploying address mints 1 WETH for itself and authorizes the Auction contract to use it. The Auction contract's buyWithPermit function, intended to allow bids through the permit mechanism, mistakenly allows any recipient to be specified for receiving the Art upon winning. Additionally, since the WETH contract lacks a permit function, attempts to use this function default to the fallback function. This results in the deposit of 0 Ether, inadvertently bypassing the expected functionality.
Leveraging the 1 WETH minted earlier, it's possible to bid and win the auction on behalf of the user, ultimately acquiring the Art NFT and completing the challenge!
A similar scenario occured in production before: if you want more information, check out this exploit post-mortem.