Missing gas_limit validation in mpp Tempo fee-payer enables wallet drain

Summary

Improper Validation of Specified Quantity in Input in ZenHive mpp allows an unauthenticated remote client to drain the fee-payer wallet, resulting in denial of service for legitimate clients. When the mpp Elixir library is configured as fee payer (fee_payer: true), the MPP.Methods.Tempo payment method co-signs and broadcasts a client-supplied EVM transaction without first validating that the client-supplied gas_limit is sufficient to complete the intended call. A malicious client can submit a signed transferWithMemo transaction with gas_limit deliberately set just below the amount required for successful execution. The server co-signs the transaction and broadcasts it via rpc_broadcast_sync. The transaction runs out of gas during EVM execution and reverts, but the fee-payer wallet is still charged for the burned gas while the client pays nothing and receives no resource. Repeated requests from one or more malicious clients drain the fee-payer wallet at near-zero cost to the attacker, ultimately preventing the server from sponsoring gas for legitimate payment requests. The wait_for_confirmation = false (optimistic) path is also affected: it invokes simulate_payment_call via eth_call, but that simulation omits the gas parameter and therefore does not catch out-of-gas conditions. This issue affects mpp: from 0.2.0 before 0.6.0.

Timeline

1. Jul 17, 2026, 10:11 AM UTCCVE published
2. Jul 17, 2026, 12:21 PM UTCCISA SSVC assessment

   Exploitation: poc · Automatable: no · Technical impact: partial

3. Jul 18, 2026, 4:12 AM UTCRecord last updated

Affected versions

• mpp

  From 0.2.0 · fixed in 0.6.0

• ZenHive/mpp

  Version range not reported

References 4