Bid Beasts
First Flight #49
Beginner FriendlyFoundrySolidityNFT
100 EXP
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Submission Details
Severity: low
Valid

Improper handling of auction settlement and event emission in `BidBeastsNFTMarket`

lochaeth

Root + Impact

Description

The AuctionSettled event is emitted when an auction is finalized, either via a regular bid settlement or a "Buy Now" purchase. In the current implementation, there is a risk that the auction settlement logic could be manipulated, allowing a malicious actor to either:

  • Prevent the previous highest bidder from being refunded correctly.

  • Influence the emitted AuctionSettled event to misrepresent auction results.

This can lead to inconsistent accounting in failed transfer credits and misleading event logs that off-chain services or dApps rely on.

function placeBid(uint256 tokenId) external payable isListed(tokenId) {
Listing storage listing = listings[tokenId];
address previousBidder = bids[tokenId].bidder;
uint256 previousBidAmount = bids[tokenId].amount;
​
require(listing.seller != msg.sender, "Seller cannot bid");
​
// auctionEnd == 0 => no bids yet => allowed
// auctionEnd > 0 and block.timestamp >= auctionEnd => auction ended => block
require(listing.auctionEnd == 0 || block.timestamp < listing.auctionEnd, "Auction ended");
​
// --- Buy Now Logic ---
​
if (listing.buyNowPrice > 0 && msg.value >= listing.buyNowPrice) {
uint256 salePrice = listing.buyNowPrice;
uint256 overpay = msg.value - salePrice;
​
// EFFECT: set winner bid to exact sale price (keep consistent)
bids[tokenId] = Bid(msg.sender, salePrice);
listing.listed = false;
​
if (previousBidder != address(0)) {
_payout(previousBidder, previousBidAmount);
}
​
// NOTE: using internal finalize to do transfer/payouts. _executeSale will assume bids[tokenId] is the final winner.
_executeSale(tokenId);
​
// Refund overpay (if any) to buyer
if (overpay > 0) {
_payout(msg.sender, overpay);
}
​
return;
}
​
require(msg.sender != previousBidder, "Already highest bidder");
@> emit AuctionSettled(tokenId, msg.sender, listing.seller, msg.value);
​
// --- Regular Bidding Logic ---
uint256 requiredAmount;
​
if (previousBidAmount == 0) {
​
requiredAmount = listing.minPrice;
require(msg.value > requiredAmount, "First bid must be > min price");
listing.auctionEnd = block.timestamp + S_AUCTION_EXTENSION_DURATION;
emit AuctionExtended(tokenId, listing.auctionEnd);
​
} else {
requiredAmount = (previousBidAmount / 100) * (100 + S_MIN_BID_INCREMENT_PERCENTAGE);
require(msg.value >= requiredAmount, "Bid not high enough");
​
uint256 timeLeft = 0;
if (listing.auctionEnd > block.timestamp) {
timeLeft = listing.auctionEnd - block.timestamp;
}
if (timeLeft < S_AUCTION_EXTENSION_DURATION) {
listing.auctionEnd = listing.auctionEnd + S_AUCTION_EXTENSION_DURATION;
emit AuctionExtended(tokenId, listing.auctionEnd);
}
}
​
// EFFECT: update highest bid
bids[tokenId] = Bid(msg.sender, msg.value);
​
if (previousBidder != address(0)) {
_payout(previousBidder, previousBidAmount);
}
​
emit BidPlaced(tokenId, msg.sender, msg.value);
}

Risk

Likelihood: Medium

  • Exploiting this requires either crafting a failed payout scenario (e.g., using a contract that rejects Ether) or manipulating the timing of bids.

  • Regular users are unlikely to encounter this unless deliberately testing edge cases.

Impact: Low

  • None directly, but can lead to financial losses indirectly

  • corrupts event logging and monitoring

Recommended Mitigation

function placeBid(uint256 tokenId) external payable isListed(tokenId) {
Listing storage listing = listings[tokenId];
address previousBidder = bids[tokenId].bidder;
uint256 previousBidAmount = bids[tokenId].amount;
​
require(listing.seller != msg.sender, "Seller cannot bid");
require(listing.auctionEnd == 0 || block.timestamp < listing.auctionEnd, "Auction ended");
// REMOVE THIS LINE:
// emit AuctionSettled(tokenId, msg.sender, listing.seller, msg.value);
// Continue with existing logic...
if (listing.buyNowPrice > 0 && msg.value >= listing.buyNowPrice) {
// ... buy now logic ...
}
- emit AuctionSettled(tokenId, msg.sender, listing.seller, msg.value);
// ... rest of function ...
}
Updates

Lead Judging Commences

cryptoghost Lead Judge about 1 month ago
Submission Judgement Published
Validated
Assigned finding tags:

BidBeasts Marketplace: Incorrect Event Emission

placeBid emits AuctionSettled even though the auction hasn’t ended, causing misleading event logs.

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