What’s Vulnerable › Vulnerabilities

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

• 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 2026-09-24
• Weakness: CWE-20

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.

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-vc9j-9wph-qghj
• https://github.com/wevm/mppx/security/advisories/GHSA-vc9j-9wph-qghj

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