Submission Details
Severity:
Integer Division Precision Loss Allows Bids Below Minimum Increment
Root + Impact
Description
Bid calculation divides before multiplying, losing precision and allowing bids below the 5% minimum increment.
// in src/BidBeastsNFTMarketPlace.sol:156
requiredAmount = (previousBidAmount / 100) * (100 + S_MIN_BID_INCREMENT_PERCENTAGE);
// @> Division first truncates remainder
For 199 wei: (199/100) * 105 = 1 * 105 = 105 wei (should be 209)
Risk
Likelihood:
-
Happens on every bid not divisible by 100
-
No validation prevents exploitation
Impact:
-
Up to 49% savings on bid increments
-
Bids under 100 wei bypass increment
-
Undermines auction fairness
Proof of Concept
function testPrecisionLoss() public {
// Case 1: Small bids get completely bypassed
uint256 previousBid = 99;
uint256 required = (previousBid / 100) * 105;
assertEq(required, 0); // Should be 104 wei, but got 0!
// Attacker can bid 1 wei instead of 104 wei
// Case 2: Larger bids still lose significant precision
previousBid = 199;
required = (previousBid / 100) * 105;
assertEq(required, 105); // Should be 209, got 105
// Attacker saves 104 wei (nearly 50% discount on increment)
// Case 3: Pattern repeats - 299 wei bid
previousBid = 299;
required = (previousBid / 100) * 105;
assertEq(required, 210); // Should be 314, got 210
// Saves another 104 wei
}
Recommended Mitigation
- requiredAmount = (previousBidAmount / 100) * (100 + S_MIN_BID_INCREMENT_PERCENTAGE);
+ requiredAmount = (previousBidAmount * (100 + S_MIN_BID_INCREMENT_PERCENTAGE)) / 100;
Updates
Lead Judging Commences
cryptoghost 2 months ago
Submission Judgement Published Assigned finding tags:
BidBeasts Marketplace: Integer Division Precision Loss
Integer division in requiredAmount truncates fractions, allowing bids slightly lower than intended.
cryptoghost 2 months ago
Submission Judgement Published Assigned finding tags:
BidBeasts Marketplace: Integer Division Precision Loss
Integer division in requiredAmount truncates fractions, allowing bids slightly lower than intended.
Rewards breakdown
nSLOC
170This contest has a flat reward structure with the following payouts:
100 EXP
20 EXP
2 EXP
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