CVE-2026-63627: mppx Gas Draining With Padding Vulnerability

MODERATE
Advisory Identifier: GHSA-727h-3vm5-qwq6
Share
CWE-20
Published
Advisory Summary

CVE-2026-63627 is a MODERATE gas draining with padding vulnerability (CWE-20: Improper Input Validation) affecting mppx libraries in the npm ecosystem. The issue involves gas draining with padding. Remediation is available by upgrading affected packages to version 0.8.2.

CVE-2026-63627 at a Glance

CVE Identifier CVE-2026-63627
GHSA Identifier GHSA-727h-3vm5-qwq6
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-20: Improper Input Validation
Affected Product mppx
Package Ecosystem npm
Published Date
Last Updated

How to Fix CVE-2026-63627

To remediate this vulnerability, upgrade all affected mppx dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

mppx fixed: 0.8.2 
npm install mppx@0.8.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls mppx

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-63627, inspect your project dependencies using npm:

npm ls mppx

Analyze the terminal output to locate any version of mppx in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.8.2), your application is affected.

Note: The npm ls mppx command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In mppx, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Details When the server acts as the fee_payer, `mppx` 0.6.27 validates calldata using viem's `decodeFunctionData`, which is lenient about trailing bytes. The `FeePayerPolicy` caps `gas_limit` (≤ 2 M) and `max_fee_per_gas` (≤ 100 Gwei) but does **not** check calldata length. Tempo uses legacy calldata gas pricing: **16 gas per non-zero byte**. Appending `N` bytes of `0x01` padding inflates actual gas used by `N × 16` while keeping `gas_limit` and `max_fee_per_gas` within policy caps. The server cosigns and broadcasts the padded transaction, draining its fee-payer wallet. **Vulnerable code path:** `FeePayerPolicy` in `fee-payer.ts` (mppx 0.6.27) enforces `maxGas = 2_000_000` and `maxFeePerGas = 100 Gwei` but has no `calldata.length` bound. The policy check passes because the inflated gas comes from intrinsic calldata cost, not the declared `gas_limit`. **Note:** In the experiment, a 16 KB `max_header_length` is enforced, which caps the maximum effective padding at roughly 5,500 bytes. The default padding in this PoC (5,500 bytes) is within that limit. ### PoC The PoC is provided below. It is configured to reproduce the attack on Tempo Moderate testnet within a Docker environment. Download the PoC and run: ```bash unzip mppx_typescript_PoC.zip cd mppx_typescript docker build -t mppx-padding . docker run --rm mppx-padding ``` There are more details in `mppx_typescript/README.md` ### Impact A malicious client can force the server to pay ~**5x** the normal transaction fee. This dramatically increases operational costs and completely destroys the profit margin on low-cost items. Please provide a way to share the PoC in .zip format to you. Thank you!

CVE-2026-63627 Affected mppx Versions

1 component(s)
Fixed Versions:
0.8.2
Product / Package Ecosystem Affected Versions Fixed Version
mppx
npm/mppx
npm
< 0.8.2
0.8.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/wevm/mppx/security/advisories/GHSA-727h-3vm5-qwq6
mppx Source Repository REPOSITORY
https://github.com/wevm/mppx/pull/602
Security Fix Commit FIX COMMIT
https://github.com/wevm/mppx/commit/24ddcca719ae282977d8747309ed1275ea282b25
mppx Source Repository REPOSITORY
https://github.com/wevm/mppx
mppx Release RELEASE
https://github.com/wevm/mppx/releases/tag/mppx@0.8.2

Frequently Asked Questions

What is CVE-2026-63627?
CVE-2026-63627 is a security vulnerability in mppx involving Gas Draining with padding under CWE-20: Improper Input Validation.
Which mppx versions are affected?
Affected versions include releases prior to 0.8.2 across affected packages: mppx.
What version fixes CVE-2026-63627?
Upgrading to 0.8.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is mppx affected?
Yes, mppx is affected in releases prior to 0.8.2. Upgrade your dependency to 0.8.2 or later.
What CWE is associated with CVE-2026-63627?
CVE-2026-63627 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check npm dependencies for CVE-2026-63627?
Run the dependency tree command: 'npm ls mppx'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-727h-3vm5-qwq6",
  "modified" : "2026-09-22T20:34:17Z",
  "published" : "2026-09-22T20:34:17Z",
  "aliases" : [ "CVE-2026-63627" ],
  "summary" : "mppx: Gas Draining with padding",
  "details" : "### Details\nWhen the server acts as the fee_payer, `mppx` 0.6.27 validates calldata using viem's `decodeFunctionData`, which is lenient about trailing bytes. The `FeePayerPolicy` caps `gas_limit` (≤ 2 M) and `max_fee_per_gas` (≤ 100 Gwei) but does **not** check calldata length.\n\nTempo uses legacy calldata gas pricing: **16 gas per non-zero byte**. Appending `N` bytes of `0x01` padding inflates actual gas used by `N × 16` while keeping `gas_limit` and `max_fee_per_gas` within policy caps. The server cosigns and broadcasts the padded transaction, draining its fee-payer wallet.\n\n**Vulnerable code path:** `FeePayerPolicy` in `fee-payer.ts` (mppx 0.6.27) enforces `maxGas = 2_000_000` and `maxFeePerGas = 100 Gwei` but has no `calldata.length` bound. The policy check passes because the inflated gas comes from intrinsic calldata cost, not the declared `gas_limit`.\n\n**Note:** In the experiment, a 16 KB `max_header_length` is enforced, which caps the maximum effective padding at roughly 5,500 bytes. The default padding in this PoC (5,500 bytes) is within that limit.\n\n### PoC\nThe PoC is provided below. It is configured to reproduce the attack on Tempo Moderate testnet within a Docker environment. Download the PoC and run:\n```bash\nunzip mppx_typescript_PoC.zip\ncd mppx_typescript\ndocker build -t mppx-padding .\ndocker run --rm mppx-padding\n``` \nThere are more details in `mppx_typescript/README.md`\n\n### Impact\nA malicious client can force the server to pay ~**5x** the normal transaction fee. This dramatically increases operational costs and completely destroys the profit margin on low-cost items.\n\nPlease provide a way to share the PoC in .zip format to you. Thank you!",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "mppx"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.8.2"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "< 0.8.1"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/wevm/mppx/security/advisories/GHSA-727h-3vm5-qwq6"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/wevm/mppx/pull/602"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/wevm/mppx/commit/24ddcca719ae282977d8747309ed1275ea282b25"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/wevm/mppx"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/wevm/mppx/releases/tag/mppx@0.8.2"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-22T20:34:17Z",
    "nvd_published_at" : null
  }
}