Securing 20-Year-Old PLCs: Non-Intrusive Approaches

The focus on securing IT environments often overshadows the equally critical need to protect operational technology (OT) environments, especially legacy systems. Programmable Logic Controllers (PLCs), some of which are over two decades old, present unique challenges due to their age, lack of built-in security features, and the critical roles they play in various industries. This post delves into non-intrusive approaches to securing these aging systems, offering a comprehensive view tailored for CISOs, IT Directors, Network Engineers, and Operators in industrial settings.

Key Concepts: Understanding Legacy PLC Vulnerabilities

To navigate the complexities of securing old PLCs, one must first grasp the technology's inherent vulnerabilities. PLCs were not designed with the thorough security architecture we consider essential today. Common vulnerabilities include:

• Outdated Protocols: Many PLCs communicate using legacy protocols like Modbus, DF1, or even Serial RS-232, which lack modern encryption and authentication methods.

• Limited Processing Power: The hardware limitations often restrict the integration of modern cybersecurity practices.

• Isolation Challenges: While air-gapping was once a common practice to secure OT environments, this approach is now often impractical due to the necessity of data sharing with IT systems.

Historically, the development of PLCs in the 1960s focused on automation and control rather than security, leaving manufacturing and infrastructure operators with a significant challenge they are forced to confront today.

Non-Intrusive Security Approaches

As organizations strive to enhance the security of their legacy PLCs without disrupting operations, non-intrusive security methods come to the forefront. Here, we outline key strategies:

1. Network Segmentation

Implementing network segmentation is an essential step in securing legacy PLCs. By isolating the PLCs from the broader IT network, organizations can restrict access and minimize exposure to potential threats.

Best Practices:

• Utilize Virtual Local Area Networks (VLANs) to create distinct segments for PLCs, ensuring that only authorized personnel or applications can communicate with these devices.

• Incorporate firewalls as gateway devices to monitor and filter traffic between segments. The rules should prioritize the least privilege principle, allowing only necessary communications.

2. Intrusion Detection Systems (IDS)

Deploying an ID system tailored to OT environments can enable organizations to detect potential breaches without directly interfacing with the PLC.

Best Practices:

• Utilize passive monitoring tools compatible with legacy protocols, enabling early detection of irregular activities while safeguarding operational integrity.

• Emerging technologies like machine learning can be integrated into IDS systems for refined anomaly detection, significantly enhancing the ability to recognize threats against PLCs.

3. Regular Audits and Compliance Checks

Establishing regular audits and compliance checks can identify vulnerabilities in PLCs and ensure adherence to industry standards.

Recommended frameworks:

• NIST SP 800-53: This framework provides a catalog of security and privacy controls that can be adapted to manage risks relevant to legacy PLC environments.

• IEC 62443: This standard focuses on the security of industrial automation and control systems, offering guidance on securing legacy equipment.

4. Secure Remote Access Solutions

As remote monitoring and access become commonplace, secure remote access solutions are paramount. Deploying VPNs specifically configured for OT can provide secure communication channels while reducing risk to PLCs.

Best Practices:

• Ensure that the VPN is kept current with patches and that encryption methods meet industry standards.

• Implement two-factor authentication for access credentials to add an additional layer of security.

IT/OT Collaboration: Fostering Effective Communication

The collaboration between IT and OT teams is crucial for effective security management. Bridging the gap requires:

• Regular Training: Cross-training sessions help both IT and OT personnel understand the unique challenges and risks associated with legacy PLCs.

• Establishing Communication Protocols: Creating structured communication channels ensures that potential security issues are reported and addressed swiftly.

Historical Perspective: The Evolution of PLC Security

A historical overview reveals how PLC security has lagged behind IT security developments. Initially built for reliability and functionality, the development of PLCs in the 60s through the 90s prioritized performance over security.

As cyberattacks have evolved, notably with incidents like the Stuxnet worm in 2010 targeting Siemens PLCs, awareness around securing PLCs has increased, leading to contemporary standards such as IEC 62443, which advocates for a proactive approach to OT security.

Conclusion: A Road Ahead for Legacy Systems

Securing 20-year-old PLCs requires a nuanced approach, balancing operational integrity with the essential need for cybersecurity. By leveraging non-intrusive methods like network segmentation, IDS, regular audits, and fostering IT/OT collaboration, organizations can enhance the security posture of vital legacy systems without introducing disruptions. The evolution of technology demands that we not only adapt but also innovate in our security practices to safeguard our industrial environments for the future. As we move forward, it's vital to adopt a mindset that integrates ongoing assessment and adaptation within the operational framework to stay ahead of emerging threats in this increasingly interconnected world.