CVE-2025-40939: Siemens SIMATIC CN 4100 · Improper Access Control
Affects Siemens SIMATIC CN 4100Source CVE Database V5
Not known to be exploited · CVSS 4.6 Medium.
Data as of 26 Oct 2026, 17:16 UTC
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 9 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| Siemens SIMATIC CN 4100 | Affected
| Fixed in– |
AI-suggested
- Enhance physical security controls around SIMATIC CN 4100 devices to prevent unauthorized physical access, including locked cabinets, restricted access zones, and surveillance.
- Monitor devices for unexpected reboots or operational anomalies that could indicate exploitation attempts.
- Implement strict access control policies for personnel with physical access to industrial control systems.
- Segregate critical devices from general access areas to reduce exposure.
- Engage with Siemens for firmware updates or patches as they become available and plan timely deployment.
- Conduct regular security audits and physical inspections of industrial environments to detect potential tampering.
- Consider additional protective measures such as USB port locks or disabling unused physical interfaces if supported by the device.
- 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.