---
id: CVE-2026-73829
title: >-
  Time-of-check Time-of-use (TOCTOU) Race Condition in ZenHive mpp allows an
  unauthenticated remote client to redeem one confirmed on-chain payment for
  multiple paid-resource accesses.


  The type="hash" credential path in MPP.Methods.Tempo.…
summary: >-
  Time-of-check Time-of-use (TOCTOU) Race Condition in ZenHive mpp allows an
  unauthenticated remote client to redeem one confirmed on-chain payment for
  multiple paid-resource accesses.


  The type="hash" credential path in MPP.Methods.Tempo.…
severity: low
cvss: 3.7
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N'
cwe:
  - CWE-367
vendor: zenhive
product: machine_payments_protocol
affected:
  - 'machine_payments_protocol >= 0.2.0, < 0.6.1'
patched:
  - machine_payments_protocol 0.6.1
published: '2026-08-19'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T18:30:09.270'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-73829'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-73829.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/ZenHive/mpp/commit/46c5b0e1311da7d92190dc7d9ea89027a1d365e9
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://github.com/ZenHive/mpp/security/advisories/GHSA-w8j7-7qc3-5f24'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-73829'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
epss: 0.00323
epssPercentile: 0.22581
ingestedAt: '2026-09-10T19:03:26.846Z'
---

## Overview

Time-of-check Time-of-use (TOCTOU) Race Condition in ZenHive mpp allows an unauthenticated remote client to redeem one confirmed on-chain payment for multiple paid-resource accesses.

The type="hash" credential path in MPP.Methods.Tempo.verify/2 guards against replay with a non-atomic check-then-mark sequence: check_hash_unused/2 reads the dedup store, an eth_getTransactionReceipt round trip verifies the payment on chain, and only then does mark_hash_used/2 write the mark. Concurrent requests carrying the same settled payment hash all pass the read before any of them writes, so each is issued a receipt. The store's atomic check_and_mark/2 primitive is available and used by the type="transaction" path, but the hash path calls plain get and put even when the configured store implements it. Exploitation requires a dedup store to be configured; the default nil store is stateless and documented as offering no replay protection at all.

This issue affects mpp: from 0.2.0 before 0.6.1.

## Affected

- `machine_payments_protocol >= 0.2.0, < 0.6.1`

## Remediation

Upgrade past the affected range:

- `machine_payments_protocol 0.6.1`