CVE-2026-63627: CWE-20: Improper Input Validation in wevm mppx
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.
AI Analysis
Technical Summary
The vulnerability in mppx's FeePayerPolicy component involved improper input validation of fee-sponsored calldata. Specifically, decodeFunctionData did not reject trailing nonzero bytes appended by clients, which increased the intrinsic calldata gas cost without exceeding gas_limit and max_fee_per_gas caps. This caused the server's fee_payer wallet to pay substantially higher transaction fees than intended. The padding was bounded by a 16 KB header limit, with demonstrated padding of about 5,500 bytes causing roughly a fivefold increase in fees. The flaw is fixed in mppx version 0.8.2.
Potential Impact
An attacker could exploit this vulnerability to cause the server fee_payer wallet to pay significantly more gas fees than required for a transaction by appending nonzero padding bytes to the calldata. This results in financial loss due to overpayment of transaction fees. There is no indication of direct compromise or control over the server, only increased cost.
Mitigation Recommendations
Upgrade to mppx version 0.8.2 or later, where this issue is fixed. No other mitigation is indicated or required.
CVE-2026-63627: CWE-20: Improper Input Validation in wevm mppx
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.
CVSS v4.0
Score 6.9medium
Affected software
wevm
mppx
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in mppx's FeePayerPolicy component involved improper input validation of fee-sponsored calldata. Specifically, decodeFunctionData did not reject trailing nonzero bytes appended by clients, which increased the intrinsic calldata gas cost without exceeding gas_limit and max_fee_per_gas caps. This caused the server's fee_payer wallet to pay substantially higher transaction fees than intended. The padding was bounded by a 16 KB header limit, with demonstrated padding of about 5,500 bytes causing roughly a fivefold increase in fees. The flaw is fixed in mppx version 0.8.2.
Potential Impact
An attacker could exploit this vulnerability to cause the server fee_payer wallet to pay significantly more gas fees than required for a transaction by appending nonzero padding bytes to the calldata. This results in financial loss due to overpayment of transaction fees. There is no indication of direct compromise or control over the server, only increased cost.
Mitigation Recommendations
Upgrade to mppx version 0.8.2 or later, where this issue is fixed. No other mitigation is indicated or required.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-17T14:11:15.482Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6ab2d808f7a7c54106a8a017
Added to database: 09/22/2026, 19:33:28 UTC
Last enriched: 09/22/2026, 19:48:47 UTC
Last updated: 09/23/2026, 01:58:06 UTC
Views: 9
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.