What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.9 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-22 · updated 2026-09-23
• Weakness: CWE-20

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 products

• wevm mppx: before 0.8.2

References

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

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