CVE-2026-63628

Published Sep 22, 2026 Modified Sep 24, 2026 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.

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EPSS — Exploit Prediction

0.0038
Probability of exploitation
0.31%
Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-20 Improper Input Validation

References

Frequently Asked Questions

What is CVE-2026-63628? +
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.
How do I check if I'm vulnerable to CVE-2026-63628? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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