Executive brief
mppx is a TypeScript library implementing the Machine Payments Protocol for handling cryptocurrency payment flows and sessions. The library contains multiple critical vulnerabilities in its payment and session handling logic that allow attackers to bypass payment requirements, replay transactions, and manipulate fee payment arrangements—enabling free transactions and disruption of payment channels without authentication requirements.
Technical details
Multiple vulnerabilities were discovered in the tempo/charge and tempo/session components, including: transaction hash replay across push/pull modes and concurrent requests, missing transfer log verification enabling free requests in pull-mode, scope confusion allowing credential reuse across routes, missing sender signatures allowing fee payer manipulation, voucher signature verification bypass, weak channel ID binding enabling voucher reuse, channel reopen without on-chain state verification, and force-close detection bypass. All vulnerabilities require no authentication and are exploitable over the network via API calls to the affected payment and session endpoints. An unauthenticated attacker can perform unauthorized transactions, manipulate fee responsibility, and grief payment channels. The vulnerabilities were fixed in version 0.4.8.
Affected products
- wevm mppx <0.4.8
Timeline
- 2026-03-26: disclosed
- 2026-03-26: patched: Fixed in version 0.4.8