CVE-2025-40938 is a vulnerability classified under CWE-798, indicating the use of hard-coded credentials in Siemens SIMATIC CN 4100 devices with firmware versions earlier than V4.0.1. Hard-coded credentials are embedded static usernames or passwords within the device firmware, which cannot be changed by the user. This flaw allows an attacker with network access to the device to leverage these credentials to gain unauthorized access without requiring authentication or user interaction. The vulnerability affects the confidentiality, integrity, and availability of the device by potentially allowing attackers to extract sensitive information, manipulate device functions, or cause denial of service. The CVSS 3.1 vector (AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H) indicates that the attack can be performed remotely over the network but requires high attack complexity, no privileges, and no user interaction. The scope is unchanged, meaning the impact is limited to the vulnerable device itself. Siemens SIMATIC CN 4100 is commonly used in industrial automation and control networks, making this vulnerability particularly critical for operational technology environments. Although no exploits have been reported in the wild, the presence of hard-coded credentials is a well-known risk factor that can be leveraged by attackers to gain persistent access. Siemens has not yet released a patch, so affected organizations must rely on network segmentation, monitoring, and access controls to mitigate risk.

For European organizations, especially those in manufacturing, energy, and critical infrastructure sectors, this vulnerability could lead to severe operational disruptions. Unauthorized access to SIMATIC CN 4100 devices could allow attackers to manipulate industrial processes, steal sensitive operational data, or cause device outages. This can result in financial losses, safety hazards, and damage to reputation. Given Siemens' strong market presence in Europe, many industrial facilities may be affected. The vulnerability's ability to compromise confidentiality, integrity, and availability simultaneously increases the risk of cascading failures in interconnected industrial systems. Additionally, regulatory compliance issues may arise if organizations fail to adequately protect these devices, potentially leading to fines or sanctions under frameworks like NIS2 or GDPR if personal data or critical services are impacted.

Immediate mitigation should focus on network-level controls such as isolating SIMATIC CN 4100 devices within dedicated industrial control system (ICS) networks and restricting access to trusted administrators only. Implement strict firewall rules to limit inbound traffic to these devices and monitor network traffic for unusual access patterns. Employ intrusion detection systems (IDS) tailored for ICS environments to detect exploitation attempts. Since no patch is currently available, Siemens customers should engage with Siemens support for guidance and monitor for firmware updates. Where possible, replace affected devices with versions V4.0.1 or later once available. Conduct thorough audits of device configurations to identify and remove any default or hard-coded credentials. Additionally, implement multi-factor authentication on management interfaces if supported, and maintain robust logging and alerting to detect unauthorized access attempts promptly.