Severity by source
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Remote unauthenticated client submits padded calldata with low complexity; sole impact is bounded financial fee-drain on the sponsor wallet (A:L), no confidentiality or integrity effect.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
Lifecycle Timeline
4Blast Radius
ecosystem impact- 3 npm packages depend on mppx (1 direct, 2 indirect)
Ecosystem-wide dependent count for version 0.8.2.
DescriptionCVE.org
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.
AnalysisAI
Fee-sponsoring servers built on mppx before 0.8.2 can be induced by any client with access to the sponsorship endpoint to pay roughly five times the intended gas fee on otherwise-valid transactions. The FeePayerPolicy validator in src/tempo/internal/fee-payer.ts decoded client-supplied calldata with viem's decodeFunctionData but never rejected trailing bytes, so an attacker could append nonzero padding to a legitimate tip20/stablecoinDex call (transfer, approve, transferWithMemo, swapExactAmountOut) and inflate intrinsic calldata gas while gas_limit and max_fee_per_gas stayed inside the policy caps the server checks. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Requires a deployment running mppx (<0.8.2) as a fee-sponsoring server where FeePayerPolicy validates client-supplied fee-sponsored calldata before paying gas. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | This is a genuine but bounded economic-griefing flaw, not a system-compromise vulnerability. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade to mppx 0.8.2, the vendor-released patch version (release tag mppx@0.8.2, commit 24ddcca719ae282977d8747309ed1275ea282b25, PR 602; advisory https://github.com/wevm/mppx/security/advisories/GHSA-727h-3vm5-qwq6). … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
Leaving vuln.today
EUVD-2026-84805
GHSA-727h-3vm5-qwq6