Compensating Controls: How to Secure Legacy OT Systems

Compensating controls are alternative security measures you use when you can't meet specific security requirements directly. This applies particularly in OT (Operational Technology) where you will often work with legacy systems not built with modern cybersecurity in mind.

For example, in a factory with machinery running on an outdated operating system, you can't patch these systems as easily as you do with IT systems because they control critical processes. So, you put compensating controls in place. 

For example, you could segment the network to isolate these machines from the rest of the corporate network. By doing this, even if the machines are vulnerable, the risk of them being exploited decreases because attackers can't easily reach them.

So, compensating controls are about finding creative and effective ways to protect your OT environments when direct compliance isn't feasible. It entails being proactive and smart with the resources and technologies you have.

Difference between compensating and primary controls

Primary controls refer to the security measures that directly address specific requirements or threats. These are the ideal solutions. For example, if a system needs regular patching to fix vulnerabilities, implementing a patch management process is a primary control. It's straightforward and tackles the problem head-on.

In contrast, compensating controls come into play when primary controls aren't possible. This often happens in OT environments because of the unique constraints you face. 

Let's say you have a legacy control system critical to production. It's so old that it no longer receives patches. Implementing a patch management process here isn't feasible. So, you turn to compensating controls.

Besides network segmentation, monitoring also serves as an effective compensating control. Since you can't secure a system with the latest security updates, deploying an advanced intrusion detection system (IDS) helps to keep a close watch for any suspicious activities. If something unusual happens, you can respond swiftly and mitigate the impact.

So, while primary controls are the ideal way to secure your OT environments, compensating controls are your backup plan. They allow you to maintain robust security even when the perfect solution isn't possible.

Why compensating controls are necessary in OT Security

In OT security, compensating controls help to navigate the tricky landscape of legacy systems and outdated technology. These older systems are often vital to operations, yet they weren't designed with today's cybersecurity threats in mind. We can't just replace them or upgrade them easily. You have to get creative and resourceful.

Take access control, for example. Sometimes, your legacy systems can't support modern authentication methods like two-factor authentication. In such cases, you might bolster physical security. 

You could implement biometric access to server rooms or use keycards. These measures ensure that only authorized personnel can access sensitive machines, adding a layer of protection.

Monitoring also plays a crucial role. Say you have a crucial system that can't be updated. You can deploy advanced intrusion detection systems (IDS) to keep an eye on it. 

By monitoring for unusual activity, you can catch potential threats early and respond quickly. This way you can stay ahead of attackers, even when using outdated tech.

Compensating controls, thus, help you to manage risks when primary controls aren't feasible. They give you the flexibility to secure your OT environments in ways that work within your constraints.

Types of compensating controls in OT Security

Administrative compensating controls

Administrative controls are policies, procedures, and practices designed to guide the behavior of your staff and manage risk effectively.

One key administrative control is the implementation of robust security policies. For instance, you might have a policy stating that all employees must undergo cybersecurity training every six months. 

This ensures that everyone is up to date with the latest threats and knows how to respond appropriately. It creates a human firewall that complements your technical defenses.

Another example is the use of detailed access control policies. Even if your legacy systems can’t support advanced authentication, you can enforce strict rules about who can access these systems. 

For example, only certain employees might have the credentials to interact with critical OT systems. These access levels are reviewed regularly to ensure they remain appropriate and aligned with your current security needs.

You can also rely on regular audits and assessments as an administrative control. Periodic security audits help you identify vulnerabilities in your OT environment. These audits might include everything from physical inspections of your facilities to reviews of your network configurations. 

Through these audits, you can spot weaknesses that compensating controls must address and continuously improve our security posture.

Incident response planning is another crucial administrative control. Having a well-defined incident response plan means you know exactly what steps to take if a security breach occurs. This plan typically includes roles and responsibilities, communication protocols, and recovery procedures. When everyone knows their role during an incident, you can respond swiftly and effectively, minimizing damage.

Vendor management also falls under administrative controls. Many companies rely on third-party vendors for various OT components and services. Ensuring that these vendors follow robust security practices is essential. 

You can achieve this by including specific security requirements in your vendor contracts and regularly reviewing their compliance. For example, you might require vendors to provide evidence of regular security assessments or certifications.

Lastly, record-keeping and documentation are vital administrative controls. Keeping detailed logs of system activities, maintenance actions, and security incidents helps you track what's happening in your OT environment. These records are invaluable for identifying patterns, understanding the scope of incidents, and meeting regulatory requirements.

These administrative controls are essential tools for creating a structured approach to managing and mitigating risks in your OT environment. They ensure that, even when you can't implement perfect technical solutions, you have a robust framework to protect your operations.

Technical compensating controls

These are compensating controls that use technology to provide alternative protection, especially when your systems can’t meet the latest security requirements directly.

One common technical control you can rely on is network segmentation. By dividing your network and placing these legacy systems in separate zones, you isolate them from the rest of your network. This makes it much harder for an attacker to move laterally if they manage to compromise one of these outdated machines.

Firewalls are another critical component in your technical toolkit. You can configure firewalls to allow only specific, necessary communications to and from your outdated systems. 

For instance, if a legacy machine only needs to talk to a particular server, you set up firewall rules to block all other traffic. This minimizes the attack surface significantly, reducing the risk of compromise.

Then there's the use of Intrusion Detection Systems (IDS) and Intrusion Prevention Systems (IPS). Say you have a crucial system that can't be updated with the latest security patches. Deploying IDS or IPS helps you monitor network traffic for suspicious activities. 

Intrusion detection and prevention systems alert you to potential threats, allowing you to react swiftly. It’s like having a security guard who never sleeps, always on the lookout for trouble.

Application whitelisting is another technique that is often used. If a legacy system can’t run modern antivirus software, you can configure it to only allow approved applications to execute. This way, even if malicious software somehow gets onto the system, it can't run. You are essentially creating a safe list of applications and blocking everything else.

You may also make use of virtual patching. Imagine you have an outdated application that's critical to your operations but hasn't been patched in ages. With virtual patching, you deploy security tools that filter and inspect traffic to and from this application, blocking exploits of known vulnerabilities. It’s not a permanent fix, but it buys you time and reduces risk considerably.

Encryption can also help. When you can’t secure the endpoints themselves, you ensure that the data they handle is encrypted. Let's say sensitive data is being transmitted over a network that includes some vulnerable nodes. Encrypting this data ensures that even if it’s intercepted, it can’t be read or tampered with easily.

Finally, you may also rely on endpoint detection and response (EDR) solutions. These tools continuously monitor the endpoints for signs of malicious activity. If something unusual is detected, they alert you right away and can even take automated actions to contain the threat.

Physical compensating controls

These compensating controls use tangible barriers and safeguards to protect your systems, especially when technical solutions aren't feasible.

One of the first controls you will consider here is physical access control. Imagine you have a legacy control system that's too outdated to support modern authentication methods. In such cases, you enforce strict physical security measures to minimize the number of people who can physically access it. 

For example, you might use biometric access to server rooms. Only authorized personnel can enter, adding an extra layer of protection. This ensures that people who do not work with server equipment don’t gain entry into the server room.

Surveillance is another powerful tool in your physical security arsenal. If you can't upgrade the software on a critical machine, you might bolster security by installing cameras and monitoring who accesses the machine. 

With real-time video feeds, you can quickly spot any unauthorized activities and respond immediately. This not only deters potential intruders but also provides a valuable audit trail if something goes wrong.

You may also use secured enclosures for sensitive equipment. Let’s say you have an old PLC (Programmable Logic Controller) that's crucial for your operations but can't be updated. 

You can place this PLC in a locked cabinet or cage. Only personnel with the right access can interact with it. This ensures that even if someone gets into the building, they still face barriers to accessing critical systems.

Environmental controls are another aspect to consider. Sometimes, protecting your systems isn't just about preventing unauthorized access. It's also about ensuring the environment is safe for these systems to operate. 

For example, legacy systems might be particularly susceptible to dust, temperature changes, or moisture. You can install air filtration systems, climate control, and moisture barriers to maintain a safe operating environment.

Let's not forget about security guards. Employing security personnel to patrol sensitive areas can be a significant deterrent. These guards are trained to notice unusual activities and can react immediately to potential threats. 

In areas where you have critical legacy systems, having a human presence adds an extra layer of security that's hard to bypass.

Physical barriers like fences and gates around your facilities also contribute to security. By controlling the perimeter, you make it harder for unauthorized individuals to gain access in the first place. 

For example, a factory with critical OT systems might have high fences, controlled entry points, and even guard posts at strategic locations.

In some cases, you might use tamper-evident seals on equipment. If you suspect that someone might try to access a device unauthorizedly, these seals give you a quick visual indication if any tampering has occurred. It might seem simple, but it's an effective way to signal potential security breaches swiftly.

Implementing these physical controls adds robust layers of protection to your OT environment. These measures ensure that even if technical controls fail or aren't possible, you have solid defenses in place to keep your systems safe.