wevm mppx up to 0.8.1 FeePayerPolicy fee-payer.ts input validation

Summaryinfo

A vulnerability was found in wevm mppx up to 0.8.1. It has been classified as problematic. Affected is an unknown function of the file src/tempo/internal/fee-payer.ts of the component FeePayerPolicy. Performing a manipulation results in input validation. This vulnerability was named CVE-2026-63627. The attack may be initiated remotely. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as problematic, was found in wevm mppx up to 0.8.1. This affects an unknown code block of the file src/tempo/internal/fee-payer.ts of the component FeePayerPolicy. The manipulation 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 integrity. The summary by CVE is:

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 that increased intrinsic calldata gas while gas_limit and max_fee_per_gas remained within policy caps, causing the server fee_payer wallet to pay substantially more than the decoded transaction required. The tested 16 KB header limit bounded the demonstrated padding to about 5,500 bytes and produced approximately five times the normal transaction fee. This issue is fixed in version 0.8.2.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-63627 since 07/17/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. Technical details are known, 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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