Threat Intelligence Database

The mpp Elixir library version 0.4.0 and other versions from 0.2.0 up to but not including 0.6.0 contain a vulnerability in the cosign_fee_payer/3 function. When the server acts as the fee payer, it does not validate gas-related parameters before cosigning transactions, allowing a malicious client to specify arbitrarily high gas fees. This causes the server to pay inflated gas costs from its own wallet, leading to direct financial loss and potential denial of service if funds are depleted.

The mpp Elixir 0.4.0 server, when acting as the fee payer, copies client-supplied EIP-2930 access lists directly into cosigned fee-payer transactions without validation. This allows an attacker to inflate transaction fees by including fabricated access list entries, causing the fee-payer to pay significantly higher gas costs without additional on-chain work. The attack can increase gas costs by approximately 7.4 times, severely impacting operational costs and profit margins for low-cost transactions.

Authentication Bypass by Capture-replay in ZenHive mpp allows an attacker holding a captured subscription activation credential to charge the payer repeatedly. The payer signs a Tempo KeyAuthorization over the chain id, key type, key id, expiry, limits and scopes only, with nothing tying it to the challenge that prompted it. MPP.Methods.Tempo.KeyAuthorization.verify/3 in lib/mpp/methods/tempo/key_authorization.ex pins each of those signed fields against the subscription request, and the access key it pins is a static per-endpoint server key, so one signed authorization verifies against every challenge the server issues for the same subscription terms. MPP.Methods.Tempo.Subscription.activate/4 deduplicates activations by challenge id, so presenting the captured credential under a fresh challenge produces a different dedup key, claim_activation succeeds, and the subscription transaction is built and broadcast again. Each replay charges the payer's wallet a new first-period settlement and re-authorizes the server key, bounded only by the subscription expiry and the chain's own semantics for re-installing an existing key. This issue affects mpp: from 0.14.0 before 0.16.2.

Improper Validation of Specified Quantity in Input in ZenHive mpp allows a client holding an open payment channel to obtain paid resources without being charged. MPP.Session.Actions.accept_voucher/3 in lib/mpp/session/actions.ex treats a voucher whose cumulativeAmount equals the channel's already-accepted cumulative amount as an idempotent success, returning the channel unchanged without calling maybe_spend/2. The credential verifies, the protected resource is served, and spent and units stay where they were. Because the server issues a fresh challenge per request and the credential replay store keys on challenge id and payload, the same signed voucher can be re-presented under every new challenge, so one paid voucher yields an unbounded number of paid units. The path is reachable from any method built on MPP.Session.Method through the Plug, MCP, JSON-RPC and WebSocket transports. This issue affects mpp: from 0.14.0 before 0.16.2.

Improper Validation of Unsafe Equivalence in Input in ZenHive mpp allows an unauthenticated remote client to pass the Tempo duplicate-submission gate twice with one signed transaction. MPP.Methods.Tempo reserves the pre-broadcast dedup slot on the caller-supplied hex in reserve_hash_atomic/2, keyed through store_key/1 on tx.raw rather than on a canonical form of the transaction. The deserializer stores the caller's hex verbatim and accepts both recovery-id encodings, so one signed transaction submitted once with v=27 and once with v=0 yields two distinct reserve keys, and both pass the reserve and reach the broadcast path. The plug-level credential replay store is deliberately carved out for tempo in lib/mpp/replay.ex, leaving this reserve as the only gate, and the post-broadcast mark writes the canonical hash key that the raw-keyed reserve never reads. What the duplicate submission yields depends on the node: a nonce-reuse rejection fails closed, while a node that answers with the canonical hash for an already-known transaction returns a second valid Payment-Receipt for a single on-chain payment. This issue affects mpp: from 0.2.0 before 0.16.2.

Use of Cache Containing Sensitive Information in ZenHive mpp allows a shared HTTP cache to store a paid response and serve it to clients that never paid. MPP.Plug.verify_credential in lib/mpp/plug.ex sets payment-receipt and cache-control: private on the connection before the wrapped application runs, and registers no register_before_send/2 callback. Plug.Conn.put_resp_header/3 replaces an existing header, so a mounting application that sets its own cache-control on the paid resource (for example public, max-age=3600) silently overrides the private the library relies on, and a CDN or reverse proxy can then store the paid 200 together with its Payment-Receipt and serve both to unpaid clients. The library-level guarantee is therefore defeatable by the application it protects. For the same reason a downstream non-2xx response still carried Payment-Receipt, issuing a receipt for a response that delivered no resource. This issue affects mpp: from 0.1.0 before 0.16.2.

CVE-2026-82750 is a high-severity vulnerability in ZenHive mpp versions from 0.2.0 up to but not including 0.16.1. It involves improper validation of the specified quantity in input, allowing unauthenticated remote clients to inflate the gas cost paid by the fee-payer for sponsored payments. Specifically, the vulnerability arises because the server does not validate the aa_authorization_list field, enabling clients to attach multiple delegations that increase the gas cost significantly. This can lead to sponsors paying excessive gas fees and clients upgrading their accounts to delegated code at the sponsor's expense.

CVE-2026-82751 is a vulnerability in ZenHive mpp that allows an unauthenticated remote client to cause a sponsor to pay significantly increased gas fees by exploiting improper validation of input quantities. Specifically, the client can attach a signed key authorization to provision a new access key with token spending limits on their own account, which the sponsor pays for. This leads to inflated gas costs and unauthorized access key creation. The issue affects versions from 0.2.0 up to but not including 0.16.1.

Authentication Bypass by Capture-replay in ZenHive mpp allows an unauthenticated remote client to obtain paid resources by resubmitting one settled on-chain transfer. MPP.Methods.EVM.verify/2 accepts a transaction-hash credential and matches a transfer purely on token, to and amount (ERC-20) or to and value (native). It binds the proof neither to the challenge being verified nor to any record of prior use, and the generic MPP.Plug dedup store keys on challenge.id, which is regenerated for every 402 response. On a static-price route, a single historical transfer matching the charge therefore satisfies an unbounded number of later charges, including transfers an attacker can read off a public block explorer. This issue affects mpp: from 0.3.0 before 0.6.3.

Allocation of Resources Without Limits or Throttling in ZenHive mpp allows an unauthenticated remote client to drain the fee-payer wallet through concurrent sponsored payments, denying service to legitimate payers once it is empty. MPP.Methods.Tempo.FeePayerPolicy enforces its ceilings (max_gas, max_fee_per_gas, max_priority_fee_per_gas, the worst-case gas_limit * max_fee_per_gas <= max_total_fee budget cap, and a validity window) against one transaction at a time, and nothing accounts for exposure across concurrent requests. reserve_hash_atomic/2 is keyed on the transaction hash, so it prevents duplicate broadcast of the same signed transaction but not N distinct sponsored transactions carrying distinct expiring nonces. Committed sponsor exposure is therefore N times max_total_fee, bounded by nothing in the library, and the default 900 second validity window lets co-signed transactions stay broadcastable and uncounted for that entire period. This issue affects mpp: from 0.2.0 before 0.12.0.