mppx vulnerabilities

mppx is a TypeScript interface for machine payments protocol. Prior to 0.8.2, the fee-payer cosigning path in src/tempo/internal/fee-payer.ts copied a client-supplied access_list from a 0x78 FeePayerEnvelope without validating its length or contents. Because EIP-2930 access-list entries consume intrinsic gas even when unused, a client could add fabricated address-only entries and cause the server fee_payer wallet to pay unnecessary transaction fees. The demonstrated 180-entry list stayed within gas and size limits while increasing fees ~9.4x. Fixed in 0.8.2.

mppx is a TypeScript interface for machine payments protocol. Prior to 0.8.2, FeePayerPolicy in src/tempo/internal/fee-payer.ts used decodeFunctionData to validate fee-sponsored calldata but did not reject trailing bytes. A client could append nonzero padding increasing intrinsic calldata gas while gas_limit and max_fee_per_gas stayed within policy caps, causing the server fee_payer wallet to pay substantially more than required. The tested 16 KB header limit bounded padding to ~5,500 bytes, producing ~5x normal fees. Fixed in 0.8.2.

mppx before version 0.4.11 did not check Stripe's Idempotent-Replayed response header when creating PaymentIntents. An attacker could replay a valid credential with the same spt token against a new challenge, and the server would accept the replayed PaymentIntent as a new payment without actually charging the customer. This allowed paying once and consuming unlimited resources.

mppx prior to version 0.4.11 contains a vulnerability in the tempo/session cooperative close handler. The close voucher amount validation uses "<" instead of "<=" against the on-chain settled amount. An attacker can submit a close voucher exactly equal to the settled amount, which is accepted without committing new funds, effectively closing the channel for free.