CVE-2026-34210
HighCVSS 8.1Exploitation Probability (EPSS)
Low risk40th percentile - higher than 40% of all known CVEs
Summary
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.
Risk Assessment
The risk involves reusing a single payment to gain unlimited resource access, leading to financial losses and system abuse.
Recommendation
Upgrade mppx to version 0.4.11 or later, which includes a fix to check the Idempotent-Replayed header.
Other vulnerabilities in mppx
See all- CVE-2026-63628Medium
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.
- CVE-2026-63627Medium
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.
- CVE-2026-34209High
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.
Original NVD description (English source)
mppx is a TypeScript interface for machine payments protocol. Prior to version 0.4.11, the stripe/charge payment method did not check Stripe's Idempotent-Replayed response header when creating PaymentIntents. An attacker could replay a valid credential containing the same spt token against a new challenge, and the server would accept the replayed Stripe PaymentIntent as a new successful payment without actually charging the customer again. This allowed an attacker to pay once and consume unlimited resources by replaying the credential. This issue has been patched in version 0.4.11.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS