ZenHive mpp CVE-2026-67581

Exploitation requires that the target application uses MPP.Methods.EVM for payment verification and operates a static-price route - meaning the charge token, recipient address, and amount are fixed or predictable across requests. The attacker must locate a historical on-chain transfer to the service's wallet address matching those exact parameters; because all Ethereum transactions are publicly visible on block explorers, this requires no special access or interception capability. The application must NOT have configured the 'store' dedup option introduced in 0.6.3 (the option was absent in affected versions). Dynamic pricing - where the charge amount varies per session - significantly limits exploitation because historical transfers are less likely to match, though does not eliminate it if an attacker can influence or predict the price. Exploitation is fully unauthenticated and network-accessible. No user interaction is required.

The CVSS 4.0 score of 8.7 (AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N) accurately reflects the ease of exploitation: no authentication, no complexity, and full network accessibility. VI:H captures the financial integrity impact - attackers obtain paid resources without payment. No EPSS score is available in the provided data, and there is no CISA KEV listing, meaning active exploitation is unconfirmed. Despite the lack of confirmed exploitation, real-world risk is elevated because the attack surface is uniquely favorable: Ethereum transactions are permanently and publicly visible on block explorers, meaning an attacker does not need to intercept traffic or compromise any system to obtain a valid transaction hash. The attack is likely automatable against static-price routes. Dynamic pricing partially constrains but does not eliminate risk. No conflicting signals exist between the CVSS vector and the description; the network vector and lack of privilege requirements are consistent with how the EVM verify endpoint is called.

An attacker queries a public block explorer such as Etherscan for historical ERC-20 or native ETH transfers to the target service's wallet address matching its advertised static price, obtaining a valid on-chain transaction hash at zero cost. The attacker submits that hash as the payment credential to the mpp-protected HTTP endpoint, which calls MPP.Methods.EVM.verify/2; the library confirms the on-chain transfer details match the charge parameters and issues a new challenge.id each request, bypassing deduplication. The attacker repeats this submission indefinitely, gaining unlimited access to paid resources using a single historical payment they did not originate.