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VulnerabilityPublished

CVE-2025-40939: Siemens SIMATIC CN 4100 · Improper Access Control

Affects Siemens SIMATIC CN 4100Source CVE Database V5

0

Not known to be exploited · CVSS 4.6 Medium.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.1 base score
4.6Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 11% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 9 Dec 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Affected software

ProductAffectedFixed in
Siemens SIMATIC CN 4100Affected
  • =0
Fixed in–

AI-suggested

  1. Enhance physical security controls around SIMATIC CN 4100 devices to prevent unauthorized physical access, including locked cabinets, restricted access zones, and surveillance.
  2. Monitor devices for unexpected reboots or operational anomalies that could indicate exploitation attempts.
  3. Implement strict access control policies for personnel with physical access to industrial control systems.
  4. Segregate critical devices from general access areas to reduce exposure.
  5. Engage with Siemens for firmware updates or patches as they become available and plan timely deployment.
  6. Conduct regular security audits and physical inspections of industrial environments to detect potential tampering.
  7. Consider additional protective measures such as USB port locks or disabling unused physical interfaces if supported by the device.
  8. Develop incident response plans that include procedures for handling denial of service caused by physical tampering.

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.

References

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