Modernizing Industrial Automation: Key Updates in IEC 61131-3:2025 and Their Cybersecurity Implications

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Introduction

The latest revision of the IEC 61131-3 standard (Edition 4.0, 2025) introduces critical updates that align industrial automation with modern software engineering practices. With additions like mutexes, semaphores, UTF-8 support, and assertions, PLC programming is evolving—but these changes also bring new cybersecurity considerations for IT/OT convergence.

Learning Objectives

  • Understand the cybersecurity risks of concurrent execution in industrial control systems (ICS).
  • Learn how to securely implement mutexes and semaphores in PLC programming.
  • Explore best practices for hardening PLCs against vulnerabilities introduced by modern software features.

1. Securing Concurrent Execution with Mutexes and Semaphores

Verified Code Snippet (Structured Text – CODESYS/TwinCAT)

VAR 
myMutex: MUTEX; 
sharedData: INT; 
END_VAR

// Lock the mutex before accessing shared data 
MUTEX_LOCK(myMutex); 
sharedData := sharedData + 1; 
// Unlock after critical section 
MUTEX_UNLOCK(myMutex);

Step-by-Step Guide

  1. Why Use Mutexes? – Prevents race conditions when multiple tasks access shared resources.
  2. Implementation – Declare a `MUTEX` variable and use MUTEX_LOCK/MUTEX_UNLOCK around critical sections.
  3. Security Risk – Deadlocks or unsecured mutexes can lead to denial-of-service (DoS) attacks. Always implement timeout mechanisms.

2. Hardening UTF-8 String Handling in PLCs

Verified Code Snippet (Structured Text)

VAR 
unsafeString: STRING(255); 
sanitizedString: USTRING(255); 
END_VAR

// Convert and sanitize input 
sanitizedString := STRING_TO_USTRING(unsafeString);

Step-by-Step Guide

  1. Threat – Malicious UTF-8 payloads can trigger buffer overflows.
  2. Mitigation – Use `USTRING` for Unicode support and validate input length.
  3. Best Practice – Implement input sanitization functions to prevent injection attacks.

3. Using ASSERT for Secure Debugging

Verified Code Snippet

VAR 
sensorValue: INT := 100; 
END_VAR

// Validate sensor input 
ASSERT(sensorValue >= 0 AND sensorValue <= 100, "Invalid sensor reading");

Step-by-Step Guide

  1. Purpose – `ASSERT` helps detect logic errors early.
  2. Security Impact – Disable asserts in production to prevent information leakage.
  3. Implementation – Use for preconditions, postconditions, and invariants.
    1. Removing Obsolete Features: Why IL Deprecation Improves Security

Legacy Risk

  • Instruction List (IL) was prone to unreadable, insecure code.
  • Mitigation – Migrate to Structured Text (ST) for better maintainability and security.

5. API Security for Modern PLCs

Example: Securing REST API in CODESYS

// Enable HTTPS and authentication 
HTTP_Server.Config.SSL.Enable := TRUE; 
HTTP_Server.Config.Authentication := TRUE;

Step-by-Step Guide

  1. Threat – Unsecured APIs expose PLCs to remote attacks.
  2. Mitigation – Enforce TLS 1.2+ and role-based access control (RBAC).

What Undercode Say

  • Key Takeaway 1: Modern PLC programming introduces software-like risks (race conditions, injection attacks).
  • Key Takeaway 2: IT/OT convergence demands cybersecurity awareness—apply secure coding practices to industrial systems.

Analysis: The IEC 61131-3:2025 update bridges industrial automation and software engineering, but without proper security measures, features like mutexes and APIs can become attack vectors. Organizations must train engineers in secure PLC programming and adopt DevSecOps for ICS.

Prediction

By 2030, PLCs will face increasing cyber threats due to greater connectivity. Proactive adoption of secure coding standards will be critical to safeguarding critical infrastructure.

IT/Security Reporter URL:

Reported By: Activity 7343297714014646272 – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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