CVE-2026-67581 in mpp
Summary
by MITRE • 08/19/2026
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.
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability identified in ZenHive's Multi-Party Payment (MPP) module represents a critical authentication bypass mechanism rooted in the failure to bind cryptographic proofs to specific, non-reusable challenges. This flaw allows an unauthenticated remote client to circumvent payment requirements by exploiting the stateless nature of the verification logic within the EVM integration layer. Specifically, the MPP.Methods.EVM.verify/2 function accepts a transaction hash as proof of payment and validates it solely based on static attributes such as token address, recipient address, transfer amount for ERC-20 tokens, or value for native assets. The system fails to associate this proof with the specific challenge ID that initiated the request, nor does it maintain any record of prior usage for that transaction hash. This architectural oversight creates a scenario where valid payment proofs can be reused indefinitely, effectively nullifying the intended access control mechanisms designed to restrict paid resources to authenticated and compensated users.
The operational impact of this vulnerability is severe, as it enables attackers to obtain unlimited access to premium services or data by resubmitting a single historical on-chain transfer that matches the required parameters. Because the deduplication logic in MPP.Plug relies exclusively on challenge.id for tracking prior verifications, and because challenge IDs are regenerated dynamically upon every 402 response, there is no persistent state linking previous successful payments to future requests. An attacker can simply observe a public block explorer to identify a past transaction that meets the criteria of a current charge—such as sending exactly one unit of a specific token to the designated address—and replay this same transaction hash in subsequent verification attempts. Since the system does not check if the proof has already been consumed, each resubmission is treated as a fresh, valid payment, allowing the attacker to bypass authentication checks repeatedly without incurring additional costs or requiring new funds on-chain.
From a security classification perspective, this vulnerability aligns with CWE-287 Improper Authentication and CWE-345 Insufficient Verification of Data Authenticity. The failure to bind the proof to the specific context of the request constitutes an identity assertion flaw where the system trusts the provided credential without verifying its uniqueness or temporal validity relative to the session. In terms of offensive security frameworks, this behavior is characteristic of ATT&CK technique T1078 Valid Accounts when applied to automated replay attacks, although in this case it applies more broadly to unauthenticated actors exploiting stateless verification logic. The exploitation vector involves capturing a legitimate transaction and replaysing it against multiple service endpoints or subsequent requests, which falls under the broader category of Replay Attacks (T1539).
To mitigate this vulnerability, developers must implement strict idempotency checks that bind each payment proof to a unique, non-reusable challenge identifier. The verification logic should maintain a persistent record of all transaction hashes that have been successfully used for authentication within a relevant timeframe or indefinitely, depending on the security model's requirements. Additionally, incorporating nonce-based validation where each request includes a random value that must be signed by the payer ensures that proofs cannot be reused across different sessions. Updating to version 0.6.3 of the mpp module is essential as it addresses these fundamental flaws in the verification process. Until such updates are applied or custom patches are implemented, organizations relying on this integration should restrict access through alternative means and monitor for unusual patterns of repeated transaction hash submissions that may indicate active exploitation attempts.