CVE-2026-67581: On-chain transfer proof is not single-use in mpp EVM payment method, enabling cross-challenge replay

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-19 · updated 2026-09-10
Weakness: CWE-294

Description

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 products

ZenHive Machine Payments Protocol: from 0.3.0 before 0.6.4 — fixed in 0.6.4

How to fix

Upgrade to a fixed version: ZenHive Machine Payments Protocol 0.6.4. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-67581 or the next vulnerability affects your stack