# CVE-2026-88255: Business logic in mpp

> Attackers can bypass duplicate submission checks by re-encoding transactions, potentially generating multiple valid receipts for a single payment.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/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:** 16 Sep 2026
- **Updated:** 16 Sep 2026
- **Also known as:** EEF-CVE-2026-88255, GHSA-8x7x-5j8g-8hcx, GHSA-p7v4-jpp9-2m3q

## What is CVE-2026-88255?

CVE-2026-88255 is a medium-severity vulnerability in ZenHive mpp, published on 16 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Improper Validation of Unsafe Equivalence in Input in ZenHive mpp allows an unauthenticated remote client to pass the Tempo duplicate-submission gate twice with one signed transaction.

MPP.Methods.Tempo reserves the pre-broadcast dedup slot on the caller-supplied hex in reserve_hash_atomic/2, keyed through store_key/1 on tx.raw rather than on a canonical form of the transaction. The deserializer stores the caller's hex verbatim and accepts both recovery-id encodings, so one signed transaction submitted once with v=27 and once with v=0 yields two distinct reserve keys, and both pass the reserve and reach the broadcast path. The plug-level credential replay store is deliberately carved out for tempo in lib/mpp/replay.ex, leaving this reserve as the only gate, and the post-broadcast mark writes the canonical hash key that the raw-keyed reserve never reads.

What the duplicate submission yields depends on the node: a nonce-reuse rejection fails closed, while a node that answers with the canonical hash for an already-known transaction returns a second valid Payment-Receipt for a single on-chain payment.

This issue affects mpp: from 0.2.0 before 0.16.2.

Weakness: CWE-1289 (Improper Validation of Unsafe Equivalence in Input)

## Which versions are affected by CVE-2026-88255?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `mpp` | Hex | From 0.2.0 | 0.16.2 |

## How do I fix CVE-2026-88255?

Upgrade mpp to 0.16.2 or later.

## Is CVE-2026-88255 being exploited?

There is no known exploitation of CVE-2026-88255 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-88255 and fix it if it is affected.

What it is: CVE-2026-88255 is a medium-severity vulnerability in ZenHive mpp, published on 16 Sep 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-2026-88255 in the wild and no public exploit code.

Affected packages and fixed versions:
- mpp (Hex): affected from 0.2.0; fixed in 0.16.2

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-2026-88255/ (Markdown: https://insights.sbomify.com/CVE-2026-88255/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-88255
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-88255
- OSV: https://osv.dev/vulnerability/CVE-2026-88255

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-88255/
Summaries are generated and may contain mistakes; the official description above is the record.