# CVE-2026-67581: On-chain transfer proof is not single-use in mpp EVM payment method, enabling cross-challenge replay

> Attackers can replay settled on-chain transfers to bypass payment verification and access paid resources in ZenHive mpp EVM payment methods.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Aug 2026
- **Updated:** 19 Aug 2026
- **Also known as:** EEF-CVE-2026-67581, GHSA-vp5h-xh25-44wf, GHSA-vrg5-xm7q-qcjh

## What is CVE-2026-67581?

CVE-2026-67581 is a high-severity authentication bypass vulnerability in ZenHive mpp, published on 19 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Authentication Bypass by Capture-replay in ZenHive mpp allows an unauthenticated remote client to obtain paid resources by resubmitting one settled on-chain transfer.

MPP.Methods.EVM.verify/2 accepts a transaction-hash credential and matches a transfer purely on token, to and amount (ERC-20) or to and value (native). It binds the proof neither to the challenge being verified nor to any record of prior use, and the generic MPP.Plug dedup store keys on challenge.id, which is regenerated for every 402 response. On a static-price route, a single historical transfer matching the charge therefore satisfies an unbounded number of later charges, including transfers an attacker can read off a public block explorer.

This issue affects mpp: from 0.3.0 before 0.6.3.

Weakness: CWE-294 (Authentication Bypass by Capture-replay)

## Which versions are affected by CVE-2026-67581?

1 open source package ship an affected version, including mpp. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mpp` | Hex | From 0.3.0 | 0.6.3 |

Products: Zenhive Machine Payments Protocol.

## How do I fix CVE-2026-67581?

Upgrade mpp to 0.6.3 or later.

## Is CVE-2026-67581 being exploited?

There is no known exploitation of CVE-2026-67581 in the wild and no public exploit code.

## Other vulnerabilities in ZenHive mpp

- [CVE-2026-73541](https://insights.sbomify.com/CVE-2026-73541/): Denial of service in mpp (high 8.3)
- [CVE-2026-73136](https://insights.sbomify.com/CVE-2026-73136/): Static memo configuration in mpp Tempo disables per-challenge attribution binding, enabling third-party replay (high 8.2)
- [CVE-2026-73829](https://insights.sbomify.com/CVE-2026-73829/): Non-atomic hash-credential dedup in mpp Tempo allows replay of a confirmed payment under a concurrent race (medium 6.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-67581 and fix it if it is affected.

What it is: CVE-2026-67581 is a high-severity authentication bypass vulnerability in ZenHive mpp, published on 19 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-67581 in the wild and no public exploit code.

Affected packages and fixed versions:
- mpp (Hex): affected from 0.3.0; fixed in 0.6.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-67581/ (Markdown: https://insights.sbomify.com/CVE-2026-67581/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-67581
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-67581
- OSV: https://osv.dev/vulnerability/CVE-2026-67581

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-67581/
Summaries are generated and may contain mistakes; the official description above is the record.