# CVE-2023-25556: Auth bypass in Merten INSTABUS Tastermodul 1fach System M 625199

> Attackers with local access can compromise KNX devices by exploiting weak authentication that accepts keys shorter than seven digits.

- **Severity:** High 8.3 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Apr 2023
- **Updated:** 5 Feb 2025
- **Also known as:** GHSA-q53x-4f23-hq3j

## What is CVE-2023-25556?

CVE-2023-25556 is a high-severity authentication bypass vulnerability in Schneider Electric Merten INSTABUS Tastermodul 1fach System M 625199, published on 18 Apr 2023. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A CWE-287: Improper Authentication vulnerability exists that could allow a device to be
compromised when a key of less than seven digits is entered and the attacker has access to the
KNX installation.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2023-25556?

It affects 7 products.


Products: Schneider-Electric Merten Instabus Tastermodul 1fach System M Firmware, Schneider-Electric Merten Instabus Tastermodul 2fach System M Firmware, Schneider-Electric Merten Jalousie-\/Schaltaktor Reg-K\/8x\/16x\/10 M. Hb Firmware, Schneider-Electric Merten Knx Argus 180\/2\,20m Up System Firmware, Schneider-Electric Merten Knx Schaltakt.2x6a Up M.2 Eing. Firmware, Schneider-Electric Merten Knx Uni-Dimmaktor Ll Reg-K\/2x230\/300 W Firmware, Schneider-Electric Merten Tasterschnittstelle 4fach Plus Firmware.

## How do I fix CVE-2023-25556?

No fix has been published for CVE-2023-25556 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-25556 being exploited?

There is no known exploitation of CVE-2023-25556 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-25556 and fix it if it is affected.

What it is: CVE-2023-25556 is a high-severity authentication bypass vulnerability in Schneider Electric Merten INSTABUS Tastermodul 1fach System M 625199, published on 18 Apr 2023. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-25556 in the wild and no public exploit code.

Affected product: Schneider Electric Merten INSTABUS Tastermodul 1fach System M 625199. 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-2023-25556/ (Markdown: https://insights.sbomify.com/CVE-2023-25556/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-25556
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-25556
- OSV: https://osv.dev/vulnerability/CVE-2023-25556

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From sbomify Insights: https://insights.sbomify.com/CVE-2023-25556/
Summaries are generated and may contain mistakes; the official description above is the record.