---
id: CVE-2026-34209
title: mppx is a TypeScript interface for machine payments protocol
summary: >-
  mppx is a TypeScript interface for machine payments protocol. Prior to version
  0.4.11, the tempo/session cooperative close handler validated the close
  voucher amount using "<" instead of "<=" against the on-chain settled amount.
  An attac…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'
cwe:
  - CWE-294
vendor: wevm
product: mppx
affected:
  - mppx < 0.4.11
patched:
  - mppx 0.4.11
published: '2026-03-31'
updated: '2026-07-24'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-34209'
references:
  - url: >-
      https://github.com/wevm/mppx/commit/94088246ee18f21b5d6be40d9e7a464f5a280bfb
    label: security-advisories@github.com
  - url: 'https://github.com/wevm/mppx/releases/tag/mppx@0.4.11'
    label: security-advisories@github.com
  - url: 'https://github.com/wevm/mppx/security/advisories/GHSA-mv9j-8jvg-j8mr'
    label: security-advisories@github.com
tags:
  - nvd
epss: 0.00436
epssPercentile: 0.35222
ingestedAt: '2026-07-24T21:39:13.402Z'
---

## Overview

mppx is a TypeScript interface for machine payments protocol. Prior to version 0.4.11, the tempo/session cooperative close handler validated the close voucher amount using "<" instead of "<=" against the on-chain settled amount. An attacker could submit a close voucher exactly equal to the settled amount, which would be accepted without committing any new funds, effectively closing or griefing the channel for free. This issue has been patched in version 0.4.11.

## Affected

- `mppx < 0.4.11`

## Remediation

Upgrade past the affected range:

- `mppx 0.4.11`