wevm mppx up to 0.8.1 Fee-Payer Cosigning Path fee-payer.ts access_list input validation

Summaryinfo

A vulnerability categorized as problematic has been discovered in wevm mppx up to 0.8.1. This affects an unknown part of the file src/tempo/internal/fee-payer.ts of the component Fee-Payer Cosigning Path. The manipulation of the argument access_list results in input validation. This vulnerability is identified as CVE-2026-63628. The attack can be executed remotely. There is not any exploit available. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in wevm mppx up to 0.8.1. It has been classified as problematic. Affected is an unknown functionality of the file src/tempo/internal/fee-payer.ts of the component Fee-Payer Cosigning Path. The manipulation of the argument access_list with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on availability. CVE summarizes:

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 the listed addresses are never used, 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 remained within the 500,000 gas policy cap, 16 KB header limit, and RPC simulation budget while increasing the fee by approximately 9.4 times. This issue is fixed in version 0.8.2.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2026-63628 since 07/17/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. There are known technical details, but no exploit is available.

Upgrading to version 0.8.2 eliminates this vulnerability.

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Productinfo

Vendor

• wevm

Name

• mppx

Version

• 0.8.0
• 0.8.1

Website

• Product: https://github.com/wevm/mppx/

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