Beyond Antivirus: Addressing the Critical Security Needs of OT

Cyberattacks are an ever-growing concern for organizations across all industries. While IT networks often benefit from a robust array of security tools, organizations relying on operational technology (OT) face unique challenges in defending against these threats. Unlike IT environments, OT systems are often unable to rely on traditional antivirus solutions. These tools, though effective in office networks, fail to address the distinct needs of industrial operations. Here’s why:

  • Static Systems: OT environments prioritize stability and uptime, often running on legacy systems that cannot accommodate regular updates or resource-intensive antivirus programs.
  • Limited Connectivity: Many OT networks are isolated or air-gapped, making it difficult to deliver frequent signature updates needed for antivirus tools to detect evolving threats.
  • Incompatibility and Performance Risks: Antivirus scans can disrupt the real-time performance OT systems demand, introducing risks to critical operations.
  • Reactive Nature: Antivirus programs focus on detecting known threats after they have emerged, leaving OT environments vulnerable to zero-day exploits and advanced persistent threats (APTs).

Given these limitations, it’s clear that OT systems need a different approach—one that emphasizes prevention over reaction. This is where allowlisting comes into play as an alternative to traditional antivirus solutions.

Table comparing features of antivirus (signature-based) and allowlisting (application control) security solutions, highlighting allowlisting's advantages in OT environments. Option 3 (Detailed): Table titled "Antivirus vs. Allowlisting" comparing signature-based antivirus and application control allowlisting across eight features: Fundamental Approach, Zero-Day & Advanced Threats, Updates, Maintenance, Performance, OT Suitability, Setup, and False Positives. Allowlisting is shown to offer superior protection against advanced threats, lower maintenance, and better suitability for OT environments. Option 4 (Most Detailed and Includes Table Data): Table titled "Antivirus vs. Allowlisting" comparing signature-based antivirus and application control allowlisting. Antivirus blocks known bad, has low protection against zero-day threats, requires frequent updates, has high maintenance overhead, can be resource-intensive, is challenging for OT due to updates, is easier to set up initially, and is more likely to produce false positives. Allowlisting allows only known good, has high protection against zero-day threats, requires infrequent updates for approved apps, has low maintenance overhead, has minimal performance impact, is well-suited to static OT systems, requires more involved initial setup, and is less likely to produce false positives.

What is Allowlisting?

Allowlisting is a proactive cybersecurity strategy that blocks unauthorized programs from running by allowing only pre-approved applications to execute. It operates on a “default deny” principle, meaning anything not explicitly permitted is automatically restricted. This approach aligns perfectly with the predictable and static nature of OT environments, offering a tailored solution for securing industrial systems.

The Benefits of Allowlisting in OT

  • Stronger Threat Prevention: By blocking unauthorized applications, allowlisting neutralizes zero-day exploits and APTs before they can take hold.
  • Reduced Attack Surface: Limiting the software that can run minimizes potential entry points for attackers.
  • Operational Stability: Preventing unapproved changes or software installation protects system integrity and reduces the risk of downtime.
  • Simplified Compliance: Allowlisting supports adherence to industry standards and frameworks like NIST, IEC 62443, and NERC CIP.
  • Alignment with Zero Trust Principles: It enforces a “never trust, always verify” approach, ensuring every application is vetted before execution.

For organizations operating in the OT space, allowlisting represents not just an alternative to antivirus, but a paradigm shift in how security is approached—proactively and with the unique needs of industrial environments in mind.

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A 5-Step Process to Secure Your OT Environment with Application Allowlisting

Implementing application allowlisting requires careful planning and execution. This 5-step process provides a proven approach for successful deployment:

Step 1: PLAN – Laying the Foundation for Success

Creating a comprehensive deployment plan is essential. This involves:

  • Asset Inventory: Conduct a thorough inventory of all hardware and software in your OT environment. This includes operating systems, applications, firmware versions, and network connections. A detailed asset inventory checklist should include: Device Name, IP Address, OS, Installed Software, Function, Criticality.
  • Tool Selection: Evaluate different application allowlisting tools based on features, compatibility with your OT systems (including legacy systems), management capabilities, and integration with existing security infrastructure. Consider vendors like Carbon Black, McAfee Application Control, and others.
  • Compatibility Assessment: Determine which systems can be protected. Most modern tools support Windows XP SP3 and later. For older systems (Windows NT, Server 2000), consider mitigation strategies like network segmentation, virtual patching, or, if possible, upgrades.
  • Deployment Method: Choose the appropriate deployment method:
    • Remote Agent Deployment: Use existing system management tools like BigFix, SCCM, Active Directory, or specialized OT security platforms like Verve Security Center.
    • Manual Installation: For systems without remote management capabilities, schedule on-site visits with operators, respecting change management procedures.
  • Change Management: Engage with OT operators early in the process and follow established change management procedures to minimize disruption to operations.
  • Performance Impact Assessment: Evaluate the potential performance impact of the allowlisting agent on HMIs and servers. Most modern solutions have minimal impact, but testing is crucial.
  • Soak Testing: Select representative systems for initial testing (“soak testing”). These should be non-critical systems that mirror production environments.

Step 2: DEPLOY – Gradual and Controlled Rollout

  • Phased Deployment: Begin by deploying the allowlisting agent to a small number of systems, following a “low and slow” approach to minimize network congestion and potential disruptions.
  • Disabled Mode Deployment: Crucially, deploy the agents in disabled (or monitoring) mode. This allows the agent to collect information about running applications without actively blocking anything. This prevents operational disruptions during initial setup. Tamper protection, while important, can cause issues if communication with the allowlisting server is interrupted.
  • Testing in a Non-Production Environment: If possible, replicate a section of your OT network in a test environment to thoroughly test the deployment and configuration before implementing changes in production.

Step 3: SIMULATE – Building an Accurate Allowlist

  • Simulation Mode: After deployment, transition the agents to simulation mode. This allows the agent to log all file execution attempts without blocking them, generating a comprehensive log of application usage.
  • Log Analysis: Analyze the simulation logs to identify legitimate applications that need to be allowlisted and any potential false positives (legitimate applications mistakenly flagged as unauthorized).
  • Collaboration with Operations: Work closely with OT operators to understand the legitimate use of applications and identify any unusual activity.
  • Duration: The simulation phase should last for a sufficient period (typically a few weeks) to capture all regular system activity and ensure an accurate allowlist.
  • Alert Configuration: Configure alerts to track blocked files during simulation. This helps validate the allowlist during the lockdown phase.

Step 4: CREATE RULES – Defining Approved Applications

  • Allowlisting Methods:
    • Publisher Allowlisting: Prioritize allowlisting based on trusted software publishers (e.g., Microsoft, Siemens, Rockwell Automation). This is the safest approach as it ensures only digitally signed and verified software is allowed.
    • Path-Based Allowlisting: Use file paths to allowlist applications installed in specific directories. This is useful for custom applications or those without digital signatures.
    • Hash-Based Allowlisting: Use cryptographic hashes to identify specific file versions. This provides the highest level of granularity but can require more management for software updates.
  • Granular Rules: Create separate allowlists for different types of systems (e.g., HMIs, engineering workstations, servers) to ensure only necessary applications are allowed on each.
  • Handling Unsigned Applications: For unsigned or custom applications, carefully evaluate their legitimacy and consider using hash-based allowlisting or creating exceptions based on file paths.
  • Trusted Directories: Create “trusted directories” for software updates and patches. Installer files placed in these directories are automatically approved by the allowlisting server, simplifying the update process. This feature should be enabled only when needed and disabled after the update is complete.

Step 5: LOCKDOWN – Enforcing the Allowlist

  • Phased Lockdown: Begin the lockdown phase by moving the previously selected “soak test” systems into lockdown mode.
  • Monitoring and Alerting: Closely monitor the systems in lockdown mode and respond promptly to any alerts indicating blocked applications.
  • Allowlist Adjustments: If legitimate applications are blocked, update the allowlist accordingly.
  • Gradual Rollout: Once the allowlist is validated on the test systems, gradually roll out the lockdown to the remaining systems, following the “low and slow” approach.
  • Ongoing Maintenance: Regularly review the allowlisting rules and logs to ensure continued effectiveness and adapt to any changes in the OT environment.

The success of this approach lies in its proactive nature. Unlike traditional reactive security methods, application allowlisting anticipates potential threats and blocks them before they can compromise critical systems. When implemented correctly, this strategy not only strengthens the overall security framework but also supports regulatory compliance and operational continuity. In a world of evolving cyber threats, allowlisting offers OT environments a dependable and future-ready defense.

Common Concerns about Application Allowlisting in OT

Rolling out new security measures often sparks questions and concerns, and application allowlisting is no exception. Organizations might worry about hurdles such as the complexity of setup, the risk of disrupting operations, potential costs, or the effort involved in managing software updates. While these are valid considerations, practical solutions exist to address each of them. Let’s break them down.

  • Complexity: While initial setup requires planning, modern allowlisting tools offer automation features and centralized management consoles to simplify ongoing maintenance. Managed security services can also provide expert support.
  • Operational Disruption: Proper planning, testing, and collaboration with operations teams minimize the risk of disruption. The simulation phase is crucial for identifying and addressing potential conflicts before lockdown.
  • Cost: While there is an initial investment, the cost of implementing application allowlisting is often significantly less than the potential cost of a security incident, including downtime, data loss, and reputational damage.
  • Software Updates: Trusted directories and flexible rule creation allow for seamless software updates and patching within a allowlisting framework.

Embracing Application Allowlisting for a Safer Future

Application allowlisting is more than just an alternative to antivirus tools in OT environments—it’s a significant step toward proactive and preventative security. Rather than attempting to keep up with an endless stream of new threats, allowlisting takes a different approach by permitting only verified and trusted applications to operate. This shift provides robust defense against zero-day attacks, simplifies operations, and meets the specific needs of industrial control systems.

Adopting allowlisting does come with its challenges. Concerns such as setup complexity, potential disruptions, costs, or the management of software updates are valid, but they are not insurmountable. With careful planning, gradual implementation, and the help of modern tools designed to simplify the process—like those offering trusted directory features—these obstacles can be addressed effectively. The five-step guide shared earlier offers organizations a clear path to transition smoothly to this model.

Given the evolving threat landscape, OT organizations need to move beyond reactive measures to safeguard critical systems. The question isn’t whether allowlisting should be implemented but how soon it can be adopted. Taking this step now can help protect vital operations and create a more resilient, secure future for your organization.

Secure Your OT Systems with Confidence

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