Beatland Festival
AI First Flight #4
Beginner FriendlyFoundrySolidityNFT
EXP
View results
Previous Next
Submission Details
Severity: medium
Valid

redeemMemorabilia() applies an off-by-one supply check that prevents the last item in each collection from ever being redeemed

jfornells

Root + Impact

Because currentItemId starts at 1 while redemption is gated by currentItemId < maxSupply, each memorabilia collection can mint
at most maxSupply - 1 items, and collections with maxSupply = 1 become completely unusable.

Description

  • The intended behavior is that a memorabilia collection configured with maxSupply = N should allow exactly N redemptions, producing item IDs from 1 through N.

  • The issue is that redeemMemorabilia() uses a strict less-than comparison against maxSupply even though currentItemId is initialized to 1. As a result, the last valid item can never be redeemed. In the edge case where maxSupply = 1, the very first redemption reverts immediately, making the collection impossible to use.

function redeemMemorabilia(uint256 collectionId) external {
MemorabiliaCollection storage collection = collections[collectionId];
require(collection.priceInBeat > 0, "Collection does not exist");
require(collection.isActive, "Collection not active");
@> require(collection.currentItemId < collection.maxSupply, "Collection sold out");
​
BeatToken(beatToken).burnFrom(msg.sender, collection.priceInBeat);
​
@> uint256 itemId = collection.currentItemId++;
uint256 tokenId = encodeTokenId(collectionId, itemId);
}

Risk

Likelihood: High

  • The issue occurs during normal protocol usage whenever users attempt to redeem the full advertised supply of any memorabilia collection.

  • The failure is deterministic because it comes from the redemption boundary condition itself, not from unusual state or privileged behavior.

Impact: Medium

  • Every memorabilia collection loses one redeemable item relative to the organizer's configured maxSupply.

  • Collections configured with maxSupply = 1 cannot be redeemed at all, directly breaking a core protocol feature.

Proof of Concept

The following test shows that a collection created with maxSupply = 1 cannot be redeemed even once, although it should allow
exactly one redemption.

function test_RedeemMemorabilia_RevertsImmediately_WhenMaxSupplyIsOne() public {
// The organizer creates an active collection with a supply of exactly 1.
vm.prank(organizer);
uint256 collectionId = festivalPass.createMemorabiliaCollection(
"Genesis Poster",
"ipfs://genesis",
10e18,
1,
true
);
​
// Give the user enough BEAT and approve FestivalPass to burn it.
vm.prank(address(festivalPass));
beatToken.mint(user1, 10e18);
​
vm.prank(user1);
beatToken.approve(address(festivalPass), 10e18);
​
// The first redemption should succeed, but instead it reverts as sold out.
vm.prank(user1);
vm.expectRevert("Collection sold out");
festivalPass.redeemMemorabilia(collectionId);
}

Recommended Mitigation

Use a supply check consistent with currentItemId starting at 1, so redemption remains valid through item maxSupply.

function redeemMemorabilia(uint256 collectionId) external {
MemorabiliaCollection storage collection = collections[collectionId];
require(collection.priceInBeat > 0, "Collection does not exist");
require(collection.isActive, "Collection not active");
- require(collection.currentItemId < collection.maxSupply, "Collection sold out");
+ require(collection.currentItemId <= collection.maxSupply, "Collection sold out");
​
BeatToken(beatToken).burnFrom(msg.sender, collection.priceInBeat);
​
uint256 itemId = collection.currentItemId++;
uint256 tokenId = encodeTokenId(collectionId, itemId);
}
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge 4 days ago
Submission Judgement Published
Validated
Assigned finding tags:

[M-03] Off-by-One in `redeemMemorabilia` Prevents Last NFT From Being Redeemed

# Off-by-One in `redeemMemorabilia` Prevents Last NFT From Being Redeemed ## Description * The `createMemorabiliaCollection` function allows an organizer to create an NFT collection that can be exchanged for the BEAT token via the `redeemMemorabilia` function by users. * The `redeemMemorabilia` function checks if `collection.currentItemId` is less than `collection.maxSupply`. However, the `currentItemId` starts with 1 in the `createMemorabiliaCollection` function. This prevents the final item (where `currentItemId` equals `maxSupply`) from being redeemed. ```Solidity function createMemorabiliaCollection( string memory name, string memory baseUri, uint256 priceInBeat, uint256 maxSupply, bool activateNow ) external onlyOrganizer returns (uint256) { require(priceInBeat > 0, "Price must be greater than 0"); require(maxSupply > 0, "Supply must be at least 1"); require(bytes(name).length > 0, "Name required"); require(bytes(baseUri).length > 0, "URI required"); uint256 collectionId = nextCollectionId++; collections[collectionId] = MemorabiliaCollection({ name: name, baseUri: baseUri, priceInBeat: priceInBeat, maxSupply: maxSupply, @> currentItemId: 1, // Start item IDs at 1 isActive: activateNow }); emit CollectionCreated(collectionId, name, maxSupply); return collectionId; } function redeemMemorabilia(uint256 collectionId) external { MemorabiliaCollection storage collection = collections[collectionId]; require(collection.priceInBeat > 0, "Collection does not exist"); require(collection.isActive, "Collection not active"); @> require(collection.currentItemId < collection.maxSupply, "Collection sold out"); // Burn BEAT tokens BeatToken(beatToken).burnFrom(msg.sender, collection.priceInBeat); // Generate unique token ID uint256 itemId = collection.currentItemId++; uint256 tokenId = encodeTokenId(collectionId, itemId); // Store edition number tokenIdToEdition[tokenId] = itemId; // Mint the unique NFT _mint(msg.sender, tokenId, 1, ""); emit MemorabiliaRedeemed(msg.sender, tokenId, collectionId, itemId); } ``` ## Risk **Likelihood**: * A legitimate user calls `redeemMemorabilia` attempting to redeem the last NFT in a collection. **Impact**: * The user fails to get the NFT, even though the redemption counter has not reached the maximum supply of the collection. ## Proof of Concept The following test shows a user trying to redeem the 10th NFT in one collection. Running `forge test --mt test_Audit_RedeemMaxSupply -vv` shows the output that the 10th redemption is reverted due to the sold out. ```Solidity function test_Audit_RedeemMaxSupply() public { vm.prank(organizer); uint256 maxSupply = 10; // Cap for memorabilia NFT collection uint256 collectionId = festivalPass.createMemorabiliaCollection( "Future Release", "ipfs://QmFuture", 10e18, maxSupply, true ); vm.startPrank(address(festivalPass)); beatToken.mint(user1, 10000e18); // Give enough BEAT for user vm.stopPrank(); vm.startPrank(user1); for (uint256 i = 0; i < maxSupply - 1; i++) { festivalPass.redeemMemorabilia(collectionId); console.log("Redeem sucess:", i + 1); // Redeem success from 1 to 9 } // 10th redeem call reverts with "Collection Sold out" vm.expectRevert("Collection sold out"); festivalPass.redeemMemorabilia(collectionId); console.log("Redeem reverted:", maxSupply); vm.stopPrank(); } ``` ## Recommended Mitigation Modify the supply check in `redeemMemorabilia` to use `<=` (less than or equal to) instead of `<`, ensuring that the final item can be redeemed. This approach is preferable to modifying the `createMemorabiliaCollection` function (which is clearly documented to start `currentItemId` at 1). ```diff // Redeem a memorabilia NFT from a collection function redeemMemorabilia(uint256 collectionId) external { MemorabiliaCollection storage collection = collections[collectionId]; require(collection.priceInBeat > 0, "Collection does not exist"); require(collection.isActive, "Collection not active"); - require(collection.currentItemId < collection.maxSupply, "Collection sold out"); + require(collection.currentItemId <= collection.maxSupply, "Collection sold out"); // allow equals // Burn BEAT tokens BeatToken(beatToken).burnFrom(msg.sender, collection.priceInBeat); // Generate unique token ID uint256 itemId = collection.currentItemId++; uint256 tokenId = encodeTokenId(collectionId, itemId); // Store edition number tokenIdToEdition[tokenId] = itemId; // Mint the unique NFT _mint(msg.sender, tokenId, 1, ""); emit MemorabiliaRedeemed(msg.sender, tokenId, collectionId, itemId); } ```

Support

FAQs

Can't find an answer? Chat with us on Discord, Twitter or Linkedin.

Give us feedback!