External risk intelligence

Siemens SIMATIC CN 4100 SSH Configuration Vulnerability Bypasses Network Isolation

CVE advisorySeverity: CRITICAL (CVSS 10.0)

CVE-2023-29131

The affected product, SIMATIC CN 4100, is an industrial communication gateway. While these devices provide network connectivity, they are typically deployed within isolated industrial control system environments behind firewalls or VPNs. Public internet exposure is not a standard configuration, and the vulnerability relates to internal SSH configuration settings.

Siemens Simatic Cn 4100 Firmware

before 2.5

Halo Surface Signal: 2 out of 5 — less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in SIMATIC CN 4100 devices that could allow an attacker to bypass network isolation due to an incorrect default SSH configuration. This issue matters because it could potentially compromise the security boundaries of industrial control systems. The main concern at this time is confirming relevance and exposure within your specific environment.

Incorrect SSH settings allow bypassing network isolation.
Critical issue impacts industrial communication gateways.
Confirm relevance and potential exposure.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by targeting the SIMATIC CN 4100 device over the network. The issue stems from an insecure default SSH configuration, which, if exploited, could allow an attacker to breach network segmentation and gain unauthorized access.

Network access required.
Default SSH configuration triggered.
Bypasses network isolation.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to bypass network isolation when supported by the advisory's conditions. This means an attacker could potentially access systems that should be separated.

Network isolation.
Bypass SSH configuration defaults.
Unauthorized network access.

Operational Fix

Recommended remediation, mitigation, and detection steps

The Siemens SIMATIC CN 4100 communication gateway, specifically all versions prior to V2.5, has a vulnerability in its SSH configuration that could allow an attacker to bypass network isolation. Real-world ownership likely falls to the industrial control system (ICS) or operational technology (OT) infrastructure team responsible for managing these gateways, potentially in coordination with the cybersecurity team for risk assessment and vendor management if the vendor needs to provide a fix or guidance. The immediate practical step is to identify all deployed SIMATIC CN 4100 devices, determine their network reachability and criticality within the industrial environment, and then plan remediation based on that risk assessment.

OT/ICS infrastructure teams likely own the issue.
Verify network isolation bypass risk.
Plan remediation based on operational criticality.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is the Siemens SIMATIC CN 4100?

The SIMATIC CN 4100 is an industrial communication gateway from Siemens. It acts as a bridge between different network environments, often used to help disparate industrial systems communicate securely. By managing data flow in industrial control systems, it serves as a critical junction for connectivity and protocol translation within factory or plant networks.

What does CVE-2023-29131 mean by incorrect SSH configuration?

This vulnerability involves a weakness class known as CWE-276, which pertains to incorrect default permissions. In this case, the device shipped with default SSH settings that were not restrictive enough. Because the configuration was set incorrectly at the factory, the device fails to properly enforce network segmentation, potentially allowing unauthorized communication to pass through the gateway.

Do I need to worry if my device is not on the open internet?

The vulnerability is triggered by network-based interaction with the gateway. While it allows an attacker to bypass network isolation, it requires network connectivity to the device itself. Simply being disconnected from the public internet does not automatically neutralize the issue if an attacker has established a presence elsewhere on your internal network where the device is reachable.

Is my SIMATIC CN 4100 likely to be exposed to this risk?

Halo Surface Signal indicates that while this is a critical issue, these gateways are usually tucked away deep inside industrial control system environments behind layers like firewalls or VPNs. Direct exposure to the public internet is not a standard or intended configuration for this hardware, which generally limits the practical reach of external attackers.

How should I respond to this CVE if I run these gateways?

Your first step is to create an inventory of all deployed SIMATIC CN 4100 units to check their firmware versions. Any device running a version earlier than V2.5 is affected. Once identified, work with your operational technology team to assess the device's specific role in your network and prioritize upgrading those that are most critical to your infrastructure.

References

cert-portal.siemens.com/productcert/pdf/ssa-313488.pdf

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.