Top 15 Common Misconfigurations in OT Networks (and Fixes)

Background: The Fading “Air Gap” and the Rise of Misconfiguration Risk

For decades, Operational Technology (OT) environments-the industrial control systems (ICS), SCADA, PLCs, and other technologies that manage physical processes-operated under the comforting, albeit false, premise of the “air gap.” The idea was simple: isolation from the corporate IT network and the public internet provided inherent security.

Today, that gap is largely a relic of the past. The drive for efficiency, remote monitoring, predictive maintenance, and Industrial Internet of Things (IIoT) integration has permanently connected OT to the IT world and, often, directly to the cloud.

This convergence has amplified the threat landscape exponentially. The challenge in OT isn’t just dealing with sophisticated state-sponsored attacks; it’s the far more common, yet equally devastating, threat posed by simple misconfigurations. These errors are the low-hanging fruit for attackers, often stemming from the unique constraints of OT: reliance on legacy systems, the priority of uptime over patching, and a historical lack of cybersecurity awareness among engineering staff.

A single misconfigured firewall rule, an unchanged default password, or an accidental internet exposure can provide the initial foothold an attacker needs to move laterally, disrupt critical processes, and inflict catastrophic physical and financial damage.

This definitive guide, leveraging the latest insights from CISA, NSA, and industry experts, breaks down the Top 15 Common Misconfigurations in OT Networks and provides the strategic, updated fixes necessary to secure your industrial environment in 2025 and beyond.

Category 1: Identity & Access Control Faults (The Keys to the Kingdom)

Weak authentication and poor privilege management are the quickest and easiest ways for an attacker to gain legitimate access to critical systems.

1. Default and Hard-Coded Credentials

Many OT devices, from PLCs and RTUs to network switches, are deployed with vendor-supplied default passwords (e.g., admin/1234) that are rarely, if ever, changed. In some legacy systems, credentials may even be hard-coded into the firmware, making them publicly known.

Impact: Trivial, unauthenticated access to critical control systems, leading to immediate compromise.
The Fix (2025 Standard):
- Mandatory Change: Establish a strict, documented process to change all default credentials during installation.
- Strong, Unique Passwords: Enforce complex, unique passwords for every device and system.
- Asset Inventory: Use an automated, passive OT Asset Inventory solution to discover and track devices using default credentials for immediate remediation.

2. Lack of Multi-Factor Authentication (MFA)

In both local and remote access scenarios, access to critical systems often relies solely on a username and password, which are highly susceptible to brute-forcing or credential stuffing.

Impact: A compromised single-factor credential grants an attacker full access for lateral movement and process manipulation.
The Fix (2025 Standard):
- Enforce MFA: Implement phishing-resistant MFA (e.g., hardware tokens, certificate-based authentication) for all remote access, administrative accounts, and critical jump servers.
- Privileged Access Management (PAM): Integrate a PAM solution to manage and rotate privileged OT credentials, injecting them only when needed.

3. Excessive Account Privileges (Over-Privileging)

Operators, engineers, and even service accounts are often granted administrator-level access across a wide array of systems-far more than their job requires-simply for convenience.

Impact: The principle of Least Privilege is violated, meaning a successful compromise of a single account can yield domain-wide control and access to all critical assets.
The Fix (2025 Standard):
- Role-Based Access Control (RBAC): Implement strict RBAC, limiting user and service account access to only the specific functions and systems required for their role.
- Audit and Restrict: Regularly audit and remove excessive privileges, especially for non-essential users and service accounts.

Category 2: Network & Segmentation Failures (The Broken Walls)

The network architecture itself, if misconfigured, provides a clear path for threats to travel from the corporate network into the heart of the industrial process.

4. Insufficient IT/OT Network Segmentation

The absence of a properly configured DMZ (Demilitarized Zone) or robust firewalls between the IT and OT environments allows threats from the typically less-secure IT network (e.g., phishing malware) to move directly into the critical OT network.

Impact: IT-borne threats-like ransomware or standard malware-can spread directly to process-controlling systems, causing plant-wide shutdowns.
The Fix (2025 Standard):
- The Purdue Model/IEC 62443: Architect the network using the principles of the Purdue Model (or the Zones and Conduits of IEC 62443).
- DMZ/Industrial Firewalls: Implement a properly configured DMZ with high-assurance, application-layer firewalls between IT and OT to strictly control and inspect all traffic.

5. Lack of Internal OT Micro-Segmentation

Even within the OT network, crucial assets like Safety Instrumented Systems (SIS) and primary PLCs are often on the same flat network segment as less-critical assets like HMIs or engineering workstations.

Impact: Once an attacker breaches the OT perimeter, a flat network allows for unimpeded lateral movement to the “crown jewel” systems that control physical operations.
The Fix (2025 Standard):
- Micro-Segmentation: Implement micro-segmentation using VLANs, virtualized firewalls, or unidirectional gateways to isolate critical assets (e.g., separate the SIS layer from the control layer).
- Least-Privelege Communication: Define and enforce strict Access Control Lists (ACLs) and firewall rules that only allow explicitly required communication paths between segments.

6. Unrestricted Internet-Facing OT Systems

Critical infrastructure assets, including HMIs, historian servers, or even PLCs, are sometimes unintentionally exposed directly to the public internet, often via misconfigured remote access tools or network settings.

Impact: Threat actors can find and exploit these exposed systems within minutes using search engines like Shodan, bypassing all perimeter defenses.
The Fix (2025 Standard):
- Asset Discovery: Perform continuous, passive asset discovery to identify all publicly-exposed OT assets.
- Remove and Isolate: Immediately remove any direct public internet connections. Route all necessary remote access through a secure, monitored VPN with MFA and an intermediate jump server.

Category 3: System Hardening & Configuration Drift (The Open Doors)

Over time, system configurations drift from their secure baseline, introducing vulnerabilities through legacy protocols, unnecessary services, and lack of foundational security checks.

7. Unsecured Legacy Protocols and Services

OT networks rely heavily on older, proprietary industrial protocols (e.g., Modbus, DNP3) that were designed without security features like authentication or encryption. Furthermore, many systems still run outdated IT protocols like Telnet, FTP, or SMBv1.

Impact: Cleartext credentials, unencrypted data transmission, and exploitation of known protocol vulnerabilities enable easy eavesdropping and command injection.
The Fix (2025 Standard):
- Disable/Replace: Disable all non-essential and insecure legacy IT protocols (Telnet, FTP, RDP) and replace them with secure alternatives (SSH, SFTP, secured VNC).
- Protocol Inspection: Deploy industrial-aware Intrusion Detection/Prevention Systems (IDPS) and firewalls capable of deep packet inspection of industrial protocols to detect malicious commands.

8. Failure to Disable Unnecessary Services and Ports

Every system, from a Windows HMI to a network switch, often runs dozens of services and has open ports that are not required for its operational function. These services represent potential attack vectors.

Impact: A bloated attack surface provides more targets for an attacker to probe, escalating privileges through an unnecessary, unmonitored service.
The Fix (2025 Standard):
- System Hardening: Implement a rigorous system hardening baseline (e.g., CIS Benchmarks tailored for OT) for all operating systems and network devices.
- Close and Audit: Disable all non-essential ports and services. Regularly audit systems to ensure they adhere to the secure baseline and detect any configuration drift.

9. Lack of Robust Backup and Recovery Plans (BDR)

While not strictly a misconfiguration, the absence of an isolated, tested, and secure backup and recovery system for PLC programs, HMI images, and configuration files makes a minor incident catastrophic.

Impact: In the event of a ransomware attack or accidental deletion, the organization cannot quickly restore operations, leading to prolonged downtime and high recovery costs.
The Fix (2025 Standard):
- 3-2-1 Strategy: Implement the 3-2-1 backup strategy (three copies of data, on two different media, with one copy off-site/air-gapped).
- Test and Isolate: Regularly test the full recovery process. Ensure OT backups are isolated from the operational network and cannot be accessed or corrupted by a threat actor who breaches the OT environment.

Category 4: Vulnerability & Patch Management Deficiencies (The Unrepaired Damage)

OT’s focus on continuity often clashes with the necessity of patching, leading to an accumulation of known, exploitable vulnerabilities.

10. Poor Patch Management Process (or None at All)

Many OT systems run on older, often unpatchable, operating systems (e.g., Windows 7/XP) or have patches deliberately deferred due to fear of impacting continuous operations.

Impact: Known vulnerabilities are left open, allowing attackers to use widely available exploit tools to compromise systems. CISA frequently highlights unpatched vulnerabilities as a top exploit vector.
The Fix (2025 Standard):
- Risk-Based Prioritization: Prioritize patching based on a risk assessment that considers both the vulnerability’s severity (CVSS score) and the asset’s criticality to the mission.
- Compensating Controls: For systems that cannot be patched, implement compensating controls like virtual patching (via host-based IPS/Firewalls) and network segmentation to mitigate the risk of exploitation.

11. Absence of a Complete OT Asset Inventory

You cannot protect what you don’t know you have. Many organizations lack a complete, real-time inventory of all connected OT devices, including their hardware, firmware versions, installed software, and known vulnerabilities (CVEs).

Impact: Unknown or “Shadow OT” devices become unmonitored entry points. The security team is unaware of which critical assets contain high-severity vulnerabilities.
The Fix (2025 Standard):
- Passive Discovery: Deploy passive, agentless OT network monitoring tools (e.g., Deep Packet Inspection) to automatically discover and baseline all industrial assets without impacting operations.
- Continuous Visibility: Link the asset inventory to a vulnerability database to maintain continuous, real-time visibility into the exposure level of every device.

12. Misconfigured Host-Based Security Controls

OT endpoints, such as HMIs and engineering workstations, often have their host-based firewalls, antivirus (AV), or application whitelisting solutions improperly configured, or worse, disabled entirely.

Impact: The host provides no defense, allowing malware to run unchecked and preventing local log data from reaching security analysts.
The Fix (2025 Standard):
- Enforce Whitelisting: Implement and enforce application whitelisting on critical endpoints to prevent unauthorized software (including malware) from executing.
- Centralized Management: Ensure host-based firewalls are enabled and managed centrally to block unnecessary inbound and outbound connections.

Category 5: Monitoring & Detection Gaps (The Invisible Threat)

Even a well-secured network can be compromised. Without proper monitoring, an attacker can operate for months undetected.

13. Insufficient Internal Network Monitoring (Blind Spots)

Reliance on traditional IT-centric Security Information and Event Management (SIEM) that cannot understand industrial protocols, or the lack of any internal monitoring, creates significant blind spots within the OT environment.

Impact: Attackers can perform reconnaissance, credential harvesting, and lateral movement using industrial protocols without generating a single alert.
The Fix (2025 Standard):
- OT-Native IDPS: Deploy an OT-aware Intrusion Detection System (IDS) that understands industrial protocols (Modbus, EtherNet/IP, etc.).
- Baseline and Anomaly Detection: Establish a baseline of “normal” operational behavior (who talks to whom, what commands are sent) and use anomaly detection to flag any deviation-a crucial step for detecting subtle attacks.

14. Unsecured or Incomplete Log Collection

Critical OT devices are not configured to send security or operational logs to a centralized logging platform, or logging settings are too restrictive, missing key events.

Impact: When an incident occurs, the security team lacks the necessary forensic evidence to determine the root cause, scope of compromise, and the attacker’s actions.
The Fix (2025 Standard):
- Centralized Logging: Ensure all network devices, jump servers, HMIs, and any log-capable control systems forward their logs to a centralized, secure SIEM/OT-DCS platform.
- Retention Policy: Implement a long-term, immutable log retention policy suitable for regulatory and forensic requirements.

15. Misconfigured Remote Access for Third Parties and Vendors

Contractors and vendors often require remote access for maintenance, but their access is often persistent, unmonitored, or shared among multiple personnel.

Impact: Uncontrolled third-party access is a leading attack vector, as threat actors can compromise a vendor’s less-secure systems to pivot into the customer’s OT network.
The Fix (2025 Standard):
- Zero Trust Remote Access: Implement a Zero Trust architecture for all third-party access. Access must be:
  - Just-in-Time (JIT): Granted only for the duration of the maintenance task.
  - Ephemeral: Through temporary, one-time credentials.
  - Fully Monitored: Session recording and strict command logging are mandatory.
  - Least Privilege: Limited only to the specific device needing service.

Final Thoughts: A Proactive Stance on OT Security

Misconfigurations aren’t vulnerabilities you patch; they are security flaws you engineer out. In the converged IT/OT world, the risk calculation is no longer theoretical-it is about real-world consequences, from safety incidents to operational collapse.

Securing your OT network in 2025 means moving beyond the outdated notion of “air-gapping” and adopting a proactive, risk-managed approach that systematically addresses these common configuration pitfalls. Continuous monitoring, rigorous adherence to least privilege, and a commitment to network segmentation, all informed by a detailed asset inventory, are the indispensable cornerstones of a resilient industrial cybersecurity posture.

The attackers will always look for the easiest way in. Don’t let your own system configuration be the welcoming mat.