5 Steps to Successful Allowlisting Deployments in OT

Beyond Antivirus: Addressing the Critical Security Needs of OT

Cyberattacks are increasing across every industry — but in OT environments, the impact is often immediate. One incident can trigger process interruptions, downtime, and safety risks that directly affect production and profitability.

Traditional antivirus still has a place, but OT environments have unique realities that can make antivirus-only protection risky or incomplete:

• Static systems & legacy assets where stability matters more than constant change

• Limited connectivity / air-gapped networks where signature updates are difficult

• Performance sensitivity where scanning can disrupt real-time operations

• Reactive protection that focuses on “known bad,” which can leave gaps for new threats

That’s why many OT teams are moving toward prevention-first controls — and application allowlisting is one of the most practical steps forward.

What Is Application Allowlisting?

Allowlisting is a proactive cybersecurity approach that operates on a default deny model: only approved applications are allowed to run, and anything not explicitly permitted is blocked.

Because OT systems typically run a predictable set of applications, allowlisting can be a strong fit — protecting endpoints from unauthorized software, scripts, and unexpected execution that often leads to incidents.

Benefits of Allowlisting in OT

When implemented correctly, allowlisting can deliver real OT outcomes:

• Stronger prevention: stops unauthorized programs before they execute

• Reduced attack surface: fewer allowed applications = fewer entry points

• Improved stability: prevents unapproved changes that cause downtime

• Better compliance support: helps align with OT governance and common standards

• More efficient security: fewer noisy alerts, more focus on real risk

• Zero Trust alignment: “never trust, always verify” at application execution level

The 5-Step OT Allowlisting Deployment Plan

Step 1: Lay the Foundation for Success

A successful rollout starts with planning that respects OT operations.

Asset inventory
Document all relevant assets: device name, IP, OS, installed software, function, and criticality.

Tool selection
Choose a solution that supports your OT systems (including legacy devices), offers centralized visibility, and fits your environment.

Compatibility assessment
Confirm what can be protected. Where older systems can’t run agents, plan compensating controls (segmentation, access restrictions, mitigation).

Deployment method

• Remote deployments (where possible)

• Manual installation for isolated or non-managed systems (planned with operations)

Change management + performance checks
Engage OT teams early. Test potential performance impact on HMIs and servers, then pick representative “pilot” systems for soak testing.

Step 2: Establish a Gradual and Controlled Rollout

OT deployments should always be “low and slow.”

• Deploy to a small group first

• Avoid network congestion and unexpected disruptions

• Start agents in monitoring/disabled mode so nothing is blocked during setup

• If possible, validate in a non-production lab environment before touching production

Step 3: Build an Accurate Allowlist

Once monitoring is stable, move into simulation mode:

• Log all execution attempts without blocking

• Analyze logs to identify legitimate apps that must be approved

• Work with operations to confirm what is “normal” and what is suspicious

• Run long enough to capture routine cycles (often a few weeks)

• Configure alerts to track what would be blocked during lockdown

Step 4: Define Approved Applications

This step is where security quality is decided.

Common allowlisting methods:

• Publisher/Signed-based allowlisting (strongest trust and often easiest long-term)

• Path-based allowlisting (helpful for custom apps but needs tighter control)

• Hash-based allowlisting (most granular but adds admin overhead during updates)

Use granular rules
Create separate policies for different system types (HMIs, engineering workstations, servers). OT systems should only run what they need — nothing more.

Handle updates safely
Use controlled processes for patching (trusted directories, maintenance windows, temporary rules that expire after updates).

Step 5: Enforce the Allowlist (Lockdown)

Now you move from planning to real protection:

• Start lockdown with your soak-test systems

• Monitor alerts closely and respond quickly

• Update allowlists when legitimate apps are blocked

• Roll out to the rest of OT in phases

• Keep rules reviewed and maintained as environments evolve

Where Staro Process Control Stands Out

A lot of allowlisting projects fail for one reason: they focus on “turning it on” instead of deploying it in a way that protects uptime, safety, and change control.

Staro Process Control helps OT teams implement allowlisting with minimal disruption by supporting:

• OT asset baselining and application mapping

• Pilot planning (monitoring → simulation → lockdown)

• Policy design by system type (HMI vs engineering vs servers)

• Safe update workflows that don’t break production

• Practical guidance that ties allowlisting into broader digital transformation and smart manufacturing goals

OT security is no longer just about detecting threats — it’s about preventing disruption. Allowlisting gives OT teams a practical way to protect critical systems by ensuring only trusted software can execute, reducing risk without sacrificing uptime.

If you’re ready to implement allowlisting the right way — with a rollout that respects operations, change windows, and production priorities — Staro Process Control can help you plan, test, and deploy a solution that strengthens security and supports long-term reliability.

Read More (Related Resources)

If you’re planning stronger OT security and smarter plant performance, these resources are worth reviewing:

Motor Control Center Software: Faster MCC Commissioning & Smarter Maintenance (Staro)
https://staro.co.za/motor-control-center-software-faster-mcc-commissioning-smarter-maintenance/

Reaching the Smart Manufacturing Peak (Staro)
https://staro.co.za/reaching-the-smart-manufacturing-peak/

Credit: Rockwell Automation’s

https://www.rockwellautomation.com/en-us/company/news/blogs/5-steps-allowlisting-OT.html

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