Vulnerability · Published Sep 22, 2026 · Assigned by GitHub_M

CVE-2026-63627mppx: Gas Draining with padding

Medium 6.9

In plain English

A medium-severity improper input validation in mppx from wevm. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)6.9Medium

Exploit odds (30 days)0.5%top 55.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	mppx	0.8.2	GHSA-727h-3vm5-qwq6

Affected products (as reported)

Vendor	Product	Versions
wevm	mppx	< 0.8.2

Weakness: CWE-20 · 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

References

https://github.com/wevm/mppx/security/advisories/GHSA-727h-3vm5-qwq6 x_refsource_CONFIRM
https://github.com/wevm/mppx/pull/602 x_refsource_MISC
https://github.com/wevm/mppx/commit/24ddcca719ae282977d8747309ed1275ea282b25 x_refsource_MISC
https://github.com/wevm/mppx/releases/tag/mppx@0.8.2 x_refsource_MISC