How to Secure 20-Year-Old PLCs in Modern Networks

How to Secure 20-Year-Old PLCs in Modern Networks

Introduction

In the world of industrial automation, Programmable Logic Controllers (PLCs) stand as the backbone of operational efficiency. However, many enterprises still rely on PLCs that are over 20 years old, often built without considering the complexities of modern cybersecurity threats. This article will explore strategies for securing legacy PLCs in contemporary network environments, focusing on historical context, the evolution of network architecture, collaborative practices between IT and OT, and best practices for secure connectivity deployment.

Understanding the Historical Context of PLCs

The inception of PLC technology dates back to the late 1960s, developed as a simpler replacement for relay-based control systems. Initially, PLCs were standalone devices, functioning primarily in closed environments and communicating over proprietary protocols. By the late 1990s, the integration of Ethernet and TCP/IP into PLC architectures heralded significant changes, allowing for interconnectivity between diverse industrial components but introducing vulnerability as well.

Legacy PLCs may have never been designed with cybersecurity in mind, relying heavily on physical security and operational isolation. Unfortunately, as industrial environments are increasingly connected to broader IT networks and the Internet, the risk of cyber threats has risen considerably.

Key Concepts: Network Segmentation and Defense in Depth

Network Segmentation:

Network segmentation is a critical strategy for limiting the impact of a cybersecurity breach. It involves dividing a network into smaller, discrete zones, each with its own security protocols. For legacy PLCs, implementing network segmentation can protect vital operational technology (OT) from potential threats originating from the IT side.

Defense in Depth:

This approach mandates multiple layers of security controls across the network. In industrial settings, this could include secured remote access solutions, intrusion detection systems (IDS), and real-time monitoring for anomalies. By enforcing layers of security, organizations elevate the barriers an attacker must overcome.

Assessing Network Architecture for Industrial Environments

When considering the integration of legacy PLCs into modern networks, it’s paramount to evaluate the existing network architecture. Several styles of architectures exist:

1. Flat Architecture

In a flat architecture, all devices reside on the same network level, typically resulting in ease of communication and management but a high security risk. Such an architecture is unsuitable for critical operational environments with legacy PLCs.

2. Hierarchical Architecture

A hierarchical architecture, often applied in modern industrial settings, promotes orderly communication through distinct layers, such as field, control, and enterprise levels. This design offers enhanced security by reducing direct network access between disparate device types.

3. Zero Trust Architecture

The zero trust model ensures that no device or user is trusted by default, regardless of its location within or outside the network perimeter. Applying a zero trust approach to legacy PLCs would involve continuous verification based on capabilities and role responsibilities, ensuring minimal access to sensitive asset networks.

Facilitating IT/OT Collaboration

The convergence of IT and OT has become a necessity rather than an option. Collaboration between these traditionally siloed departments can lead to enhanced security postures and operational efficiencies. Here are strategies to enhance interoperability:

1. Cross-Departmental Training:

Regular training sessions can help staff from both domains understand each other’s terminologies, priorities, and operational paradigms, facilitating smoother communication and collaboration.

2. Unified Security Policies:

Developing integrated security policies that encompass both IT and OT can ensure both areas adhere to similar security frameworks.

3. Joint Incident Response Teams:

Creating cross-functional teams for incident management ensures varied expertise is applied during security events, leading to quicker recovery and rectification.

Best Practices for Secure Connectivity Deployment

As organizations begin to deploy secure connectivity solutions for legacy PLCs in modern networks, several best practices must be considered.

1. Secure Remote Access Protocols:

Consider deploying Virtual Private Network (VPN) solutions that restrict access to authenticated users, augmented with multi-factor authentication (MFA) to ensure secure remote access to PLCs.

2. Regular Firmware Updates:

Even if the PLC is vintage, stay updated with any available patches or firmware updates from manufacturers. This practice resolves vulnerabilities while often leading to improved performance.

3. Anomaly Detection and Monitoring:

Real-time monitoring systems can track communications to and from PLCs, identifying unusual behavior patterns that indicate potential intrusions or security breaches.

4. Comprehensive Documentation:

Maintain robust device documentation, including network configurations, operational protocols, and historical incident reports, which can be invaluable during audits and incident investigations.

Conclusion

Securing 20-year-old PLCs within modern network environments presents challenges, notably due to their inherently limited design for cybersecurity. However, by understanding historical context, employing robust network architectures, fostering IT/OT collaboration, and implementing best practices for secure connectivity deployment, organizations can protect legacy PLCs against contemporary cyber threats. As the industrial landscape continues to evolve, proactive and informed security strategies will be critical in safeguarding critical infrastructure against emerging risks.

By embracing these practices, organizations can ensure operational resilience while enabling their technology to function effectively in increasingly interconnected environments.