CVE-2026-54754 — Vulnerability in github.com/klever-io/klever-go —...

## Summary When a marketplace order is settled (`MarketBuy` / `BuyItNow`, and auction `Claim`), the buyer's payment is split three ways — **referral**, **royalties**, and the **seller (market-order owner) remainder**: ``` marketOwnerAmount = CurrentBid − referralAmount − royaltiesAmount ``` Referral and royalties are paid out **unconditionally**, but the seller remainder is only paid **when positive** (`computeMarketOwnerAmount` returns `Ok` and pays nothing when the amount is `<= 0`). When `referral% + royalty%` exceeds 100% of the bid, `marketOwnerAmount` goes **negative** and is silently skipped — so the marketplace pays out **more KLV / sale currency than the buyer paid in**, minting the difference out of thin air. The combined ceiling `royalty% + referral% <= 100%` **is** checked once, at listing time (`Sell`). But the two percentages are sourced asymmetrically at settlement: - **referral %** is **snapshotted** into the order at `Sell` (`MarketOrderData.ReferralPercentage`); - **royalty %** is **never snapshotted** — it is read **live** from the asset at buy time (`asset.Royalties.MarketPercentage`). So the listing-time invariant is a **time-of-check/time-of-use** guarantee only. After a valid listing, the asset owner raises the royalty `MarketPercentage` via `AssetTrigger → UpdateRoyalties`; at the next buy the live royalty plus the snapshotted referral exceed 100%, and the settlement mints the overflow. The minted funds land in attacker-controlled referral / royalty addresses. This was **actively exploited on mainnet** (see *Evidence*), minting tens of millions of KLV before the emergency guard was deployed. ## Affected component - Repository: `klever-io/klever-go` (node). - Settlement / mint site: `core/kapp/market/market.go` — `executeBuyMarket` (L575+), `computeReferralAmount` (L361+), `computeRoyaltiesAmount` (L490+), `computeRoyaltiesFixedDeposit` (L443+), `computeMarketOwnerAmount` (L540+). - TOCTOU sources: `Sell` combined check (`market.go:908`), order snapshot of referral but **not** royalty (`market.go:997`), live royalty mutation via `core/kapp/kda/trigger.go` — `handleUpdateRoyaltiesNFTandSFT` (L613+, sets `asset.Royalties.MarketPercentage` at L670). - Reachable from both `Buy` (BuyItNow, `market.go:204+`) and auction `Claim` (`market.go:705`, `market.go:731`). - Pre-fix: **not** gated by any fork flag — exploitable on mainnet. The fix is gated behind the new `FixMarketBuyOverflow` activation-epoch flag. --- ## Root cause ### 1. Settlement pays referral + royalty unconditionally, seller remainder only if positive `core/kapp/market/market.go` — `executeBuyMarket` (L575+): ```go referralAmount, _ := tools.ComputePercentageI64(marketOrder.CurrentBid, int64(marketOrder.ReferralPercentage), ...) // L583: SNAPSHOT referral % royaltiesAmount, _ := tools.ComputePercentageI64(marketOrder.CurrentBid, int64(asset.Royalties.MarketPercentage), ...) // L587: LIVE royalty % marketOwnerAmount := marketOrder.CurrentBid - referralAmount - royaltiesAmount // L591: can go negative // ---- FIX (FixMarketBuyOverflow), added by the patch ---- if m.forkController.FixMarketBuyOverflow() && marketOwnerAmount < 0 { // L593-596 ctx.Receipts().AddError(ctx.ContractID(), common.ErrFieldInvalidRoyalties, common.ErrInvalidValue.Error()) return transaction.Transaction_AmountInvalid, common.ErrInvalidValue } m.computeReferralAmount(ctx, marketOrder, referralAmount, currencyID) // pays referral in full m.computeRoyaltiesFixedDeposit(ctx, marketOrder, asset) // pays fixed royalty (KLV) m.computeRoyaltiesAmount(ctx, marketOrder, asset, currencyID, royaltiesAmount) // pays % royalty in full m.computeMarketOwnerAmount(ctx, marketOrder, currencyID, marketOwnerAmount) // <-- skips when <= 0 ``` `computeMarketOwnerAmount` (L540-542) — the silent skip: ```go func (m *marketKapp) computeMarketOwnerAmount(... marketOwnerAmount int64) (... , error) { if marketOwnerAmount <= 0 { return transaction.Transaction_Ok, nil // negative seller share dropped, NO error } // ... AddToBalance(marketOwnerAmount) ... } ``` Meanwhile `computeReferralAmount` (L376) and `computeRoyaltiesAmount` (L515) each `AddToBalance(...)` the full computed amount with **no matching debit** from the buyer beyond the single `bidderAcc.SubFromBalance(amount)` taken in `Buy` (`market.go:301`). **Conservation breaks:** buyer is debited `bid` once; recipients are credited `referralAmount + royaltiesAmount`. When that sum `> bid`, the surplus `(referralAmount + royaltiesAmount − bid)` is **minted**. ### 2. The combined ≤100% invariant is enforced only at listing time `Sell` (`market.go:908`) correctly rejects a listing whose combined cut exceeds 100%: ```go if asset.Royalties.MarketPercentage + marketplace.ReferralPercentage > core.HundredPercent { return transaction.Transaction_ParameterInvalid, common.ErrInvalidValue } ``` …and snapshots **referral** into the order, but **not** royalty (`market.go:997-998`): ```go marketOrder := &kapps.MarketOrderData{ // ... ReferralPercentage: marketplace.ReferralPercentage, // snapshotted RoyaltiesFixedDeposit: asset.Royalties.MarketFixed, // snapshotted // NOTE: asset.Royalties.MarketPercentage is NOT snapshotted -> read live at buy } ``` `MarketOrderData` has no field for the royalty percentage (`kapps/market.pb.go`), so settlement always re-reads it live from the (mutable) asset. ### 3. Royalty % is mutable after listing `core/kapp/kda/trigger.go` — `handleUpdateRoyaltiesNFTandSFT` (L613+) lets the asset owner overwrite `asset.Royalties.MarketPercentage` (L670) with only a **per-field** `<= 100%` check (`CheckValid100Params`, L651) — it has no knowledge of any outstanding marketplace listing's snapshotted referral. So the owner can list at, e.g., referral 100% / royalty 0% (sum 100%, passes `Sell`), then raise royalty to 100%, making the buy-time sum 200%. > The shipped emergency-guard source documents this exact vector: > *"The royalty percentage is read live at buy time, so a listing made now can be weaponised later > via UpdateRoyalties."* (`common/emergencyGuard.go`) **Net effect:** `referralAmount + royaltiesAmount = bid + bid = 2·bid`; `marketOwnerAmount = −bid` (skipped); **`bid` KLV minted per settlement**, paid to attacker-controlled addresses. --- ## Proof of Concept ### A. Committed regression test (deterministic, runnable today) `core/kapp/market/market_test.go` — `TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation`. It builds an order with `ReferralPercentage = 100%` and an asset with `MarketPercentage = 100%` (the attacker is both the referral and the royalty address), then settles a `bid` of `25,600,000 KLV` (`25600000000000` base units): ```bash go test ./core/kapp/market/ -run TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation -v ``` - `FixDisabled_MintsKLVFromThinAir`: settlement returns `Ok`; the attacker address ends with `2·bid` credited while only `bid` was paid in — i.e. **`bid` KLV minted**. - `FixEnabled_RejectsInflation`: with `FixMarketBuyOverflow` on, settlement returns `Transaction_AmountInvalid` and the attacker balance stays `0` — **no payout runs**. ### B. End-to-end on a local node (the real attack path) A single-node local network is sufficient. The exploit is four transactions from one ordinary funded account; nothing privileged is required. 1. **Create an NFT collection** you own, with `royalties.marketPercentage = 0` and a royalties address you control. 2. **Create a marketplace** with `referralPercentage = 10000` (100%) and a referral address you control (`CreateMarketplace`). 3. **List** one NFT for sale (`Sell`) on that marketplace. The `Sell` check passes because `0 (royalty) + 10000 (referral) = 10000 = HundredPercent`. The order snapshots `ReferralPercentage = 10000`. 4. **Raise the royalty** on the asset to 100% (`AssetTrigger / UpdateRoyalties`, `marketPercentage = 10000`). Allowed: the per-field check passes and the live combined invariant is never re-evaluated against the open listing. 5. **Buy** the listing (`MarketBuy`) from a second account (or settle the auction via `Claim`). `referralAmount = bid`, `royaltiesAmount = bid`, `marketOwnerAmount = −bid` (skipped). Your referral + royalty addresses receive `2·bid`; the buyer paid `bid`; **`bid` KLV is minted**. Because the attacker controls buyer, seller, referral and royalty addresses, the only real cost is transaction fees; the cycle is repeatable until supply targets are met. --- ## Evidence ### Regression test (local, verbatim) ``` === RUN TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation === RUN TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation/FixDisabled_MintsKLVFromThinAir === RUN TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation/FixEnabled_RejectsInflation --- PASS: TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation (0.00s) --- PASS: TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation/FixDisabled_MintsKLVFromThinAir (0.00s) --- PASS: TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation/FixEnabled_RejectsInflation (0.00s) PASS ok github.com/klever-io/klever-go/core/kapp/market 0.279s ``` `FixDisabled` asserts the attacker balance equals `2·bid = 51,200,000 KLV` for a single settlement (`bid = 25,600,000 KLV`), with `bid` of that minted. `FixEnabled` asserts rejection and a `0` balance. ### Mainnet exploitation (observed) The bug was exploited in production, and was **detected and characterised externally** by the community monitoring project **[KleverPuls / kpulse.tech](https://kpulse.tech)** before the root cause was known internally. Over a ~24h window kpulse isolated a single wallet (opened **2026-06-04**, ~**204 transactions** in ~24h, funded only by a ~**242K KLV KuCoin withdrawal**, no treasury/foundation funding) that: - **self-issued 3 NFT collections named "InflationPOC"** and **wash-traded one (`NFLATION-ESGO/1`) 29 times** through self-created marketplaces — ~**$450K of artificial, economically empty NFT volume**; - **swapped the proceeds KLV → USDC / USDT / WBTC / WETH on KleverSwap** and **bridged ~$72K of value to Ethereum** via wrapped-asset burns over 24h (USDC −12,487 ≈ $12.5K; USDT −26,362 ≈ $26.4K; WBTC −0.31 ≈ $19.6K; WETH −7.55 ≈ $14K); - surfaced a spurious **"1.86B KLV outflow"** headline that kpulse correctly identified as a wash-trade **receipt-doubling** artifact with small real net KLV flow. That "doubling of marketplace receipts" is **precisely the on-chain signature of this bug**: each abusive settlement pays out a referral cut (`bid`) **plus** a royalty cut (`bid`) while the buyer paid only `bid` once — the market contract emits ~2× the value it took in, which *is* the mint. The attacker's self-issued collection and self-created marketplaces are exactly the self-dealing setup the regression test reproduces (the test reuses the real on-chain identifiers: `collectionID = "NFLATION-ESGO"`, asset `1`, market name "Inflation Market"). kpulse could not determine the cause from on-chain data alone and flagged the activity for confirmation; the Klever core team then traced it to the referral+royalty settlement defect described above and shipped the emergency guard + protocol fix. Each abusive settlement minted one `bid` of KLV; the observed `bid` was `25,600,000 KLV`, repeated and funnelled through a short hop chain before being swapped and bridged. The emergency guard (`common/emergencyGuard.go`) blocks the following observed sender public keys (hex): | Public key (hex) | Address | Role (observed) | |---|---|---| | `54ea28e527d4136508be955374afa54a8c25c19a48c674f412f7ce02db0f4e1b` | `klv12n4z3ef86sfk2z97j4fhfta9f2xztsv6frr8faqj7l8q9kc0fcdsfjfqez` | root / minter | | `bb687dbba23e1844fec674a32cb8809f0d3207506c53fc3d637e40dc56708d63` | `klv1hd58mwaz8cvyflkxwj3jewyqnuxnyp6sd3flc0tr0eqdc4ns343skngdjq` | collector hop (~125M KLV) | | `77388d3dfe6cd88e8da723254c11abf3d9cccb6fb77b000e5038fc3ff92b964d` | `klv1wuug6007dnvgard8yvj5cydt70vuejm0kaasqrjs8r7rl7ftjexsglalf6` | direct recipient (25.6M, idle) | | `a196789b026f996867f08317cc6c5a4eb9ad3a59b1be3716420bc8692d4c3048` | `klv15xt83xczd7vkselssvtucmz6f6u66wjekxlrw9jzp0yxjt2vxpyq2nawrw` | hop-2 recipient (25M) | The single-`bid` per-settlement size (25.6M KLV) matches the "direct recipient, 25.6M" entry, and the ~125M at the collector hop is consistent with roughly five abusive settlements. --- ## Impact - **Unbounded inflation of KLV** (and of any sale currency used for the listing), repeatable for only transaction fees, by any account that creates its own collection + marketplace. - The minted KLV is created by direct `AddToBalance` to attacker addresses (no tracked `Mint`), so the asset's booked supply does not change — the inflation is **off the books** and only detectable by summing balances / auditing receipts (it surfaces on-chain as *doubled* marketplace receipts). - **Realized impact (observed):** the attacker minted KLV via ~29 self-dealt settlements, swapped to stable/wrapped assets on KleverSwap, and **off-ramped ~$72K to Ethereum via the bridge** (USDC, USDT, WBTC, WETH) before the emergency guard halted the activity, alongside ~$450K of artificial NFT wash-trade volume. - Total loss of economic integrity for all KLV / token holders. ## Who can exploit it / prerequisites - **Any account** that can pay the one-time collection-create + marketplace-create fees and tx fees. No roles, admin, or allowlist. - **Any client.** The settlement is triggered by standard `MarketBuy` / `Claim` contracts POSTed to the public, unauthenticated `/transaction/send` RPC (`network/api/transaction/routes.go`, `SendTX` / `BroadcastTX`). The `operator` CLI, the SDKs, or a hand-signed `curl` all work. - Deterministic; the abusive state is reached with one extra `UpdateRoyalties` after a normal listing. --- ## Remediation Shipped as a layered response (embargoed): ### Layer 0 — emergency guard (deployed first, fork-proof) — `GHSA-p7gw` rc1 `common/emergencyGuard.go` + `data/transaction/emergencyGuard.go`: matching transactions are kept out of blocks this node proposes (`core/process/block/preprocess/transactions.go`) and refused at the node API (`node.go` `SendTransaction` / `SendBulkTransactions`). It **never changes block validity**, so a partial-fleet rollout cannot fork the chain. It blocks the known attacker senders (all contract types) plus all `MarketBuy`, `Sell`, and `CreateMarketplace` / `ConfigMarketplace` operations while the protocol fix rolls out. Enforcement is by proposer cooperation, not protocol — coverage equals the share of block producers running the guard. ### Layer 1 — protocol fix (consensus, epoch-gated) — `GHSA-p7gw` rc2 `core/kapp/market/market.go:593` rejects the settlement when `marketOwnerAmount < 0`, **before any payout runs**, returning `Transaction_AmountInvalid`. Gated behind the new `FixMarketBuyOverflow` activation-epoch flag (`config/enableEpochs.*`, `core/fork/forks.go`, `core/interface.go`) so historical blocks reprocess identically. Covered by `TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation`. ### Recommended hardening (defense in depth) 1. **Snapshot the royalty %** into `MarketOrderData` at `Sell` (as referral already is) and pay from the snapshot, eliminating the TOCTOU entirely; or re-evaluate the combined `referral% + royalty% <= 100%` invariant at settlement. 2. Treat a **negative** seller remainder as a hard error everywhere, and only treat exactly `0` as a no-op skip (`computeMarketOwnerAmount`), so a future regression aborts the tx instead of minting. 3. After splitting a payment pool, **assert conservation** (`referral + royalties + ownerShare == bid`) so any drift aborts the transaction. --- ## Notes - Triggered by both BuyItNow (`Buy`) and auction settlement (`Claim`). - The same family of "pay full cut, silently drop the negative remainder" minting also exists in the royalty-split paths and is tracked separately under **GHSA-cgc5-v3f2-8m2v** (split-royalty `uint32` overflow). This advisory covers the top-level referral+royalty > bid case; the `FixMarketBuyOverflow` guard here only checks `marketOwnerAmount`, not intra-split over-payments. ## Acknowledgments - **[KleverPuls / kpulse.tech](https://kpulse.tech)** — community monitoring project that **first detected and characterised the exploitation in the wild**. kpulse isolated the attacker wallet and its "InflationPOC" collections, identified the marketplace wash-trading of `NFLATION-ESGO/1` and the KleverSwap → bridge off-ramp (~$72K to Ethereum), and flagged the anomalous *doubling* of marketplace receipts — the exact on-chain signature of this bug — prompting the incident response that led to this fix. The root cause was then identified and remediated by the Klever core team. ## Source - Vulnerable / fixed code: `core/kapp/market/market.go:540-545,575-596,908,997-998`, `core/kapp/kda/trigger.go:613-676`, `core/process/kda/assetHelper.go:101`, `tools/converters.go:102`, `core/constants.go:18`. - Emergency guard: `common/emergencyGuard.go`, `data/transaction/emergencyGuard.go`, `core/process/block/preprocess/transactions.go`, `node/node.go`. - Fork flag: `config/enableEpochs.go`, `config/node/enableEpochs.yaml`, `core/fork/forks.go`, `core/interface.go`. - Regression test: `core/kapp/market/market_test.go` (`TestMarketKApp_ExecuteBuyMarket_RoyaltyReferralInflation`).