C-1 No NFT Escrow — Sellers Never Transfer NFTs

Contract: nft-marketplace.clar · list-nft, buy-nft

The marketplace never takes custody of NFTs. list-nft creates a map entry but never calls nft-transfer?. buy-nft sends STX to the seller but never delivers the NFT to the buyer. A seller can list, collect payment, and the buyer receives nothing.

;; list-nft: only creates a map entry
(map-set listings listing-id { seller: tx-sender, ... })
;; No nft-transfer? to escrow

;; buy-nft: pays seller, never delivers NFT
(try! (stx-transfer? seller-amount tx-sender seller))
;; No nft-transfer? to buyer

The same issue applies to create-auction and end-auction — NFTs are never escrowed or delivered.

C-2 Auction Bids Not Escrowed — Free Bidding

Contract: nft-marketplace.clar · place-bid

Bids are recorded but bidder funds are never transferred. Only a balance check is performed:

(asserts! (>= (stx-get-balance tx-sender) bid-amount) err-insufficient-funds)
;; No stx-transfer? — funds stay with bidder

When end-auction settles, it attempts stx-transfer? from the winner who may no longer have sufficient funds. Previous bidders' funds are never refunded because they were never collected.

C-3 claim-buyout-proceeds Sends STX to Itself

Contract: nft-fractional.clar · claim-buyout-proceeds

The as-contract block makes tx-sender refer to the contract itself, so funds transfer from contract → contract (a no-op):

;; Inside as-contract, tx-sender = contract principal
(try! (as-contract (stx-transfer? share-of-buyout tx-sender tx-sender)))
;; Contract sends to itself — fraction holders get nothing

All buyout proceeds are permanently locked. The outer tx-sender (the claimer) must be captured in a let binding before entering as-contract.

C-4 claim-collateral Sends Collateral to Contract, Not Owner

Contract: nft-rental.clar · claim-collateral

Identical as-contract bug — collateral from delinquent renters is transferred from the contract back to itself:

(try! (as-contract (stx-transfer? (get collateral-paid rental) tx-sender tx-sender)))
;; NFT owner never receives the collateral

C-5 No NFT Custody in Fractional, Rental, or Staking Contracts

Contracts: nft-fractional.clar, nft-rental.clar, nft-staking.clar

None of these contracts transfer NFTs into escrow:

• Fractional: fractionalize-nft creates a vault but the owner retains the NFT. They can sell fractions and then transfer the NFT away — fraction holders own shares of nothing.
• Rental: rent-nft charges rent and collateral but the NFT remains with the owner. The "rental" is purely bookkeeping with no on-chain access control.
• Staking: stake-nft records a stake but the NFT remains freely transferable. Users can earn staking rewards while selling their NFT elsewhere.

C-6 Anyone Can List or Auction Any NFT

Contract: nft-marketplace.clar · list-nft, create-auction

Neither function verifies that tx-sender owns the specified NFT. Combined with C-1, an attacker lists someone else's NFT, a buyer pays, and the attacker collects the funds.

H-1 Hardcoded Treasury Address

Contract: nft-marketplace.clar

(define-constant treasury 'SP2PEBKJ2W1ZDDF2QQ6Y4FXKZEDPT9J9R2NKD9WJB)

Cannot be updated if the key is lost or compromised. All platform fees become irrecoverable.

H-2 No Duplicate Listing Prevention

Contract: nft-marketplace.clar

The same NFT can be listed multiple times simultaneously. A seller creates multiple listings for the same token and collects payment from multiple buyers. No per-NFT active listing tracking exists.

H-3 Batch Mint Hardcoded to 10, Overcharges for count > 10

Contract: nft-collection.clar · mint-batch

;; Charges for `count` tokens...
(try! (stx-transfer? (* mint-price count) tx-sender contract-owner))
;; ...but only iterates 10 times
(fold mint-single (list u1 u2 u3 u4 u5 u6 u7 u8 u9 u10) ...)

If count = 20, user pays for 20 tokens but only receives 10. The excess payment is stolen.

H-4 Buyout Price Manipulation by Vault Owner

Contract: nft-fractional.clar · update-fraction-price

The vault owner can change the fraction price at any time, which recalculates the buyout price as total-fractions × new-price × 2. After selling fractions cheaply, the owner raises the price to make buyout prohibitively expensive, trapping minority shareholders.

H-5 Rental Platform Fee Goes to Immutable contract-owner

Contract: nft-rental.clar

Platform fees are sent to contract-owner (a constant set at deploy time). Unlike a configurable treasury, this address can never be changed.

M-1 Integer Truncation in Fee Calculations

Contracts: nft-marketplace.clar, nft-rental.clar

For small prices, (/ (* price 250) 10000) truncates to zero. Platform collects no fee on trades under 40 STX (marketplace) or small rental amounts.

M-2 Approval System Has No Effect

Contract: nft-collection.clar

The transfer function only checks (is-eq tx-sender sender) but never checks token-approvals or operator-approvals. The entire ERC-721-style approval system is decorative — approved operators cannot transfer tokens.

M-3 Token URIs Are All Identical

Contract: nft-collection.clar · mint

(map-set token-uris token-id (concat (var-get base-uri) ""))

Concatenates base URI with empty string. All tokens get the same metadata URI. Token ID is never appended.

M-4 Royalties Recorded But Never Enforced

Contract: nft-collection.clar, nft-marketplace.clar

royalty-info and calculate-royalty exist in the collection contract, but the marketplace's buy-nft never calls them. Creators receive no royalty payments on secondary sales.

M-5 emergency-withdraw Can Underflow reward-pool

Contract: nft-staking.clar

(var-set reward-pool (- (var-get reward-pool) amount))

No bounds check. If amount > reward-pool, the subtraction causes an underflow panic, bricking the function.

M-6 Expired Listings Still Cancellable

Contract: nft-marketplace.clar · cancel-listing

No check for expiry or active status. Users can "cancel" already-expired or already-purchased listings.

M-7 Staking Rewards Without Actual Lock

Contract: nft-staking.clar

Since NFTs are never escrowed (C-5), stakers earn rewards based on lock duration while the NFT remains freely transferable. A user could "stake" an NFT, sell it on a marketplace, and continue earning staking rewards.

M-8 Anyone Can Fund Reward Pool

Contract: nft-staking.clar · add-to-reward-pool

No access control on pool funding. Combined with emergency-withdraw (admin-only), this enables a bait-and-switch: temporarily fund the pool to attract stakers, then drain it.