---
id: CVE-2026-63628
title: mppx is a TypeScript interface for machine payments protocol
summary: >-
  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…
severity: medium
cvss: 6.9
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N'
cwe:
  - CWE-20
vendor: wevm
product: mppx
affected:
  - mppx < 0.8.2
patched:
  - mppx 0.8.2
published: '2026-09-22'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T15:17:26.803'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63628'
references:
  - url: >-
      https://github.com/wevm/mppx/commit/24ddcca719ae282977d8747309ed1275ea282b25
    label: security-advisories@github.com
  - url: 'https://github.com/wevm/mppx/pull/602'
    label: security-advisories@github.com
  - url: 'https://github.com/wevm/mppx/releases/tag/mppx@0.8.2'
    label: security-advisories@github.com
  - url: 'https://github.com/wevm/mppx/security/advisories/GHSA-vc9j-9wph-qghj'
    label: security-advisories@github.com
  - url: 'https://github.com/wevm/mppx/security/advisories/GHSA-vc9j-9wph-qghj'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://github.com/advisories/GHSA-vc9j-9wph-qghj'
tags:
  - nvd
  - cve.org
  - exploit-available
  - ghsa
  - npm
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-24T14:17:05.530463Z'
cvssSource: cna
epss: 0.00384
epssPercentile: 0.29687
aliases:
  - GHSA-vc9j-9wph-qghj
ecosystem: npm
ingestedAt: '2026-09-22T20:10:15.110Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-63628)

Affected packages:

- `mppx < 0.8.2`

Patched in:

- `mppx 0.8.2`

Source: https://github.com/advisories/GHSA-vc9j-9wph-qghj