Dria
Swan
NFTHardhat
21,000 USDC
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Submission Details
Severity: medium
Invalid

`platformFee` cap at `100%` denies Agents their share of listing fee

tigerfrake

Summary

The platformFee parameter in setMarketParameters() allows the owner to set the fee to 100%, enabling the owner to take the entire buyerFee in transferRoyalties() and leaving nothing for the Agent. Since Agents are intended to receive a percentage of the fee, allowing platformFee to reach 100% effectively denies them this incentive, violating the intended benefit structure for Agents.

Vulnerability Details

When a seller lists their asset for sale via a given Agent, they have to pay % of the listing price as buyerFee which gets split in two ways in transferRoyalties():

function transferRoyalties(AssetListing storage asset) internal {
// calculate fees
uint256 buyerFee = (asset.price * asset.royaltyFee) / 100;
>> uint256 driaFee = (buyerFee * getCurrentMarketParameters().platformFee) / 100; // Possible (driaFee = buyerFee)
​
// first, Swan receives the entire fee from seller
// this allows only one approval from the seller's side
token.transferFrom(asset.seller, address(this), buyerFee);
​
// send the buyer's portion to them
>> token.transfer(asset.buyer, buyerFee - driaFee); // Agent gets nothing
​
// then it sends the remaining to Swan owner
>> token.transfer(owner(), driaFee); // Owner takes all
}

Every Agent has a set royaltyFee which determines the % pay. It is therefore the seller's responsibility to choose an Agent that best suits them.

However, the Agents do not get to choose what percentage the owner will set as platformFee in the market parameters.

function setMarketParameters(SwanMarketParameters memory _marketParameters) external onlyOwner {
>> require(_marketParameters.platformFee <= 100, "Platform fee cannot exceed 100%"); // Issue here
_marketParameters.timestamp = block.timestamp;
marketParameters.push(_marketParameters);
}

Also during initialization:

function initialize(
>> SwanMarketParameters calldata _marketParameters,
---SNIP---
) public initializer {
__Ownable_init(msg.sender);
​
>> require(_marketParameters.platformFee <= 100, "Platform fee cannot exceed 100%"); // Issue here
---SNIP---
}

Notice that these functions allow for the platformFee to be set to exactly 100% or less. When set to 100%, driaFee will equal the whole buyerFee which means that Swan owner will take the whole sum leaving nothing for the Agent.

Impact

According to Contest Details:

Each agent has a fee rate where the asset creators pay a % of the listing price as a fee to the agent.

Agents are entitled to a cut and setting platformFee to 100% denies them this incentive.

Tools Used

Manual Review

Recommendations

Ensure the platformFee falls below 100%.

- require(_marketParameters.platformFee <= 100, "Platform fee cannot exceed 100%");
+ require(_marketParameters.platformFee < 100, "Excess fee");
Updates

Lead Judging Commences

inallhonesty Lead Judge 12 months ago
Submission Judgement Published
Invalidated
Reason: Non-acceptable severity

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