CVE-2026-67581: On-chain transfer proof is not single-use in mpp EVM payment method, enabling cross-challenge replay
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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
zenhive/mppto a version that resolves this vulnerability.Fixed in 0.6.3
Event History
Frequently Asked Questions
Which deployments are exposed?
Deployments using mpp versions 0.3.0 through versions before 0.6.3 are affected. Exposure applies to EVM payment verification on static-price routes.
What does an attacker need to replay a payment?
An attacker needs a settled on-chain transaction hash for a transfer whose token and amount, or native-transfer recipient and value, match the route's charge. The transfer can be historical and may be obtained from a public block explorer.
Are repeated uses of the same transaction prevented by the standard deduplication mechanism?
No. The deduplication store is keyed by challenge.id, and a new challenge ID is generated for each 402 response, so it does not prevent the same proof from being used across later challenges.
How can I determine whether a route is vulnerable?
Check whether the route uses EVM payment verification, has a static charge, and runs an affected mpp version. Such a route can accept a previously settled matching transfer without binding it to the current payment challenge.