# CVE-2025-40939: Denial of service in SIMATIC CN 4100

> An attacker with physical access can trigger a reboot via the USB port, causing a denial of service on the SIMATIC CN 4100.

- **Severity:** Medium 5.1 (`CVSS:4.0/AV:P/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **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:** 9 Dec 2025
- **Updated:** 9 Dec 2025
- **Also known as:** GHSA-35wm-hq5r-2p36

## What is CVE-2025-40939?

CVE-2025-40939 is a medium-severity denial of service vulnerability in Siemens SIMATIC CN 4100, published on 9 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A vulnerability has been identified in SIMATIC CN 4100 (All versions < V4.0.1). The affected device contains a USB port which allows unauthenticated connections. This could allow an attacker with physical access to the device to trigger reboot that could cause denial of service condition.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2025-40939?

It affects 1 product.


Products: Siemens Simatic Cn 4100 Firmware.

## How do I fix CVE-2025-40939?

No fix has been published for CVE-2025-40939 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-40939 being exploited?

There is no known exploitation of CVE-2025-40939 in the wild and no public exploit code.

## Other vulnerabilities in Siemens SIMATIC CN 4100

- [CVE-2024-32741](https://insights.sbomify.com/CVE-2024-32741/): Hardcoded credentials in SIMATIC CN 4100 (critical 10.0)
- [CVE-2023-29130](https://insights.sbomify.com/CVE-2023-29130/): Privilege escalation in SIMATIC CN 4100 (critical 9.9)
- [CVE-2024-32740](https://insights.sbomify.com/CVE-2024-32740/): Hardcoded credentials in SIMATIC CN 4100 (critical 9.8)
- [CVE-2023-49621](https://insights.sbomify.com/CVE-2023-49621/): Hardcoded credentials in SIMATIC CN 4100 (critical 9.8)
- [CVE-2025-40938](https://insights.sbomify.com/CVE-2025-40938/): Hardcoded credentials in SIMATIC CN 4100 (critical 9.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40939 and fix it if it is affected.

What it is: CVE-2025-40939 is a medium-severity denial of service vulnerability in Siemens SIMATIC CN 4100, published on 9 Dec 2025. 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-2025-40939 in the wild and no public exploit code.

Affected product: Siemens SIMATIC CN 4100. 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-2025-40939/ (Markdown: https://insights.sbomify.com/CVE-2025-40939/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40939
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40939
- OSV: https://osv.dev/vulnerability/CVE-2025-40939

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40939/
Summaries are generated and may contain mistakes; the official description above is the record.