# CVE-2026-71256: nanoMODBUS Client-Side Out-of-Bounds Read Leading to Wild-Pointer Write via object_id

> A remote attacker can trigger a wild-pointer write via an out-of-bounds read in the nanoMODBUS library, potentially leading to code execution or denial of service.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 5 Aug 2026
- **Updated:** 10 Aug 2026
- **Also known as:** GHSA-vq4c-5vwv-g86v

## What is CVE-2026-71256?

CVE-2026-71256 is a critical memory corruption vulnerability in debevv nanoMODBUS, published on 5 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

nanoMODBUS through v1.23.0 contains an out-of-bounds stack read leading to a wild-pointer write in nmbs_read_device_identification_basic / recv_read_device_identification_res in nanomodbus.c. A fixed 3-element stack array order[3] = {0,1,2} maps object IDs to buffer indices. The server-supplied object_id field (0-255, read directly from the wire) is used without any bounds check as buf_index = order[object_id].

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-71256?


## How do I fix CVE-2026-71256?

No fix has been published for CVE-2026-71256 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-71256 being exploited?

There is no known exploitation of CVE-2026-71256 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-71256 and fix it if it is affected.

What it is: CVE-2026-71256 is a critical memory corruption vulnerability in debevv nanoMODBUS, published on 5 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-2026-71256 in the wild and no public exploit code.

Affected product: debevv nanoMODBUS. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-71256/ (Markdown: https://insights.sbomify.com/CVE-2026-71256/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-71256
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-71256
- OSV: https://osv.dev/vulnerability/CVE-2026-71256

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-71256/
Summaries are generated and may contain mistakes; the official description above is the record.