In today’s industrial landscape, Operational Technology (OT) environments are no longer isolated silos. From energy utilities and smart manufacturing to oil & gas and pharma automation, OT networks are deeply intertwined with IT systems, cloud services, remote support tools, modern IIoT platforms, and advanced analytics pipelines.
This hyper-connectivity has not only improved efficiency-but also dramatically expanded the potential attack surface.
While most organizations conduct periodic OT/ICS security audits, a surprising number of critical gaps still remain unnoticed, primarily because traditional audit frameworks were built around IT-centric views, compliance checklists, and outdated assumptions about industrial environments.
The result?
Even “mature” industrial plants face risks that can lead to production shutdowns, safety incidents, environmental damage, ransomware propagation, and nation-state exploitation.
This article uncovers the Top 15 OT security gaps commonly missed during audits, backed by real-world field experience, evolving threat trends, and lessons learned from industry incidents.
Why OT Security Audits Still Miss Critical Gaps
Even well-designed audit frameworks frequently fail in OT settings due to:
- Legacy systems with no built-in security
- Air-gap assumptions still used in reports
- Limited OT visibility tools compared to IT
- Lack of SME support for field devices
- Multi-vendor environments with unclear responsibilities
- Rapid convergence of IT-OT-IoT-Cloud ecosystems
- Limited downtime windows for testing or validation
- OT staff prioritizing availability > security
Most importantly, OT audits often rely on documentation instead of hands-on validation, creating blind spots that become long-term cybersecurity liabilities.
Top 15 OT Security Gaps Commonly Missed During Audits
Below are the most frequently overlooked weaknesses, explained with updated industrial cybersecurity insights and practical implications.
1. Incomplete OT Asset Inventory & Unmanaged Legacy Devices
Even in 2025, many OT environments still lack a real-time, authoritative asset inventory.
Commonly missed elements include:
- PLC rack modules
- Safety controllers
- Remote I/O
- Serial-to-Ethernet converters
- Wireless HMIs
- Engineering workstations
- Temporary vendor laptops
- Shadow IIoT sensors added during modernization
Without an accurate inventory, no risk assessment can be reliable.
Why it’s missed:
Traditional audits look at CMDBs or Excel sheets instead of validating in-field and live network visibility.
2. Unsupported, End-of-Life (EoL) OT Systems Still in Production
Critical assets-PLC firmware, RTUs, HMIs, historians, OPC servers-are often running:
- Outdated firmware
- Unsupported OS (XP, Win7, embedded systems)
- Obsolete hardware that cannot be patched
These assets become permanent zero-day exposure points.
Why it’s missed:
Audits focus on installed software versions, not vendor support cycles or firmware lifecycle reviews.
3. Dangerous Flat Network Architecture (Lack of Network Segmentation)
Audit reports may confirm VLAN usage, but VLAN ≠ segmentation.
Real issues include:
- Flat L2 broadcast domains across multiple plants
- Direct IT-to-OT routes
- Engineering workstations reachable from corporate networks
- Vendor remote support devices sitting in production zones
True segmentation requires:
- Industrial DMZ
- Secure conduits
- Firewalls between zones
- Enforced access policies
Why it’s missed:
Auditors rely on network diagrams-not packet-flow validation or firewall rule analysis.
4. Misconfigured or Weak Firewall Rules
Firewalls exist-but the rules are poorly configured:
- “Allow Any – Any” rules for vendor connections
- Open inbound ports to controllers
- Unused and forgotten rules spanning years
- Dual-purpose firewalls serving both IT and OT functions
Why it’s missed:
Audits often check presence of firewalls, not the quality of their configurations.
5. Remote Access Channels Hidden from Audit Scope
Modern OT environments rely heavily on remote support, often through:
- TeamViewer, AnyDesk, LogMeIn
- Vendor-provided VPNs
- Cellular modems
- Temporary wireless access points
- Engineering laptops with dual NICs
- Cloud dashboards for IIoT devices
These become stealthy entry points for attackers.
Why it’s missed:
Many connections are temporary, unmanaged, or maintained by third-party vendors-not listed in official documentation.
6. Unmonitored Changes in PLC Logic & Firmware
A massive blind spot in OT security:
Unauthorized or accidental logic changes in controllers.
Examples include:
- Modified ladder logic
- Altered setpoints
- Disabled alarms
- Changed safety interlocks
- Firmware backdoors
Few audits check for:
- Controller configuration drift
- Firmware mismatches
- Unauthorized engineering workstation access
7. Insecure IIoT Devices Added During Digital Transformation
IIoT adoption introduces risks rarely validated during audits:
- Wireless sensors
- Smart compressors
- Predictive maintenance gateways
- Edge compute devices
- Cloud-connected HMIs
Most come with:
- Hardcoded credentials
- Open debug ports
- Weak encryption
- Cloud dependencies
- Hidden remote access functionality
Why it’s missed:
IIoT devices are often installed by operations or vendors, outside cybersecurity governance.
8. Lack of OT-Specific Logging & Monitoring
Traditional SIEMs or SOCs rarely detect OT threats because:
- Logs not forwarded
- Proprietary protocols not understood
- PLC events not monitored
- ICS anomaly detection not deployed
- Engineer laptops have no EDR
- OT network traffic isn’t baselined
As a result, incidents go undetected for months.
9. Weak or Shared Credentials in OT Systems
Common issues:
- Default passwords on PLCs and HMIs
- Shared admin credentials for maintenance staff
- Vendor accounts with persistent access
- Passwords stored in notebooks or plant walls
- No MFA on remote access
- Lack of account lifecycle management
Why it’s missed:
Audits often check password policies-not actual device configurations.
10. Unsafe USB & Portable Media Practices
USB-borne threats (ex: Stuxnet, Conficker, Flame) still plague OT.
Gaps include:
- Engineering laptops with unrestricted USB ports
- Portable drives used for PLC updates
- Unscanned maintenance USBs
- Lack of data diode protections
- No removable media monitoring or isolation zones
11. Absence of Backup & Recovery Testing for OT Systems
Most plants “have backups” but…
- They are outdated
- They were never restored or tested
- PLC programs exist only on engineer laptops
- Server snapshots are corrupted
- Safety controller backups are missing
In industrial downtime events, this becomes a disaster.
12. Insufficient Physical Security & Device Tamper Monitoring
OT assets often sit in:
- Unlocked cabinets
- Remote substations
- Outdoor enclosures
- Vendor containers
- Unmanned control rooms
Physical access = full compromise.
Why it’s missed:
Audit teams rarely inspect field devices physically.
13. Overlooked Third-Party & Supply Chain Cyber Risks
Vendors often have:
- Direct remote access
- Privileged system accounts
- Firmware update authority
- Unmonitored support tunnels
- Software supply chain dependencies
Audits generally focus only on internal controls, ignoring external attack vectors.
14. Lack of OT Incident Response (IR) Preparedness
Many organizations still use IT-centric IR playbooks that are incompatible with OT realities.
Common missing elements:
- Engineering SME involvement
- Asset isolation procedures
- Emergency shutdown coordination
- Forensic imaging for PLCs
- OT-safe threat containment steps
- 24×7 SOC with ICS expertise
During a real attack, this causes chaos.
15. Misalignment Between IT, OT & Cybersecurity Teams
One of the biggest but least visible gaps:
- IT teams enforce policies that break OT operations
- OT teams bypass policies for uptime
- Cyber teams lack visibility into industrial risk
- Vendors operate independently
- Responsibilities are unclear during incidents
This cultural divide creates systemic, long-term security issues that no checklist can capture.
How Organizations Can Close These Security Gaps
Based on global OT cybersecurity best practices, organizations should:
1. Build a Living OT Asset Inventory
- Use passive monitoring
- Validate field assets
- Track firmware & configurations
2. Implement True OT Network Segmentation
- Industrial DMZ
- Zones & conduits
- Role-based access
3. Strengthen Remote Access Governance
- MFA
- Time-bound access
- Session recording
4. Deploy OT-Specific Monitoring
- Deep packet inspection for ICS protocols
- Behavior anomaly detection
- Controller integrity monitoring
5. Enforce Vendor/Supply Chain Security
- Contractual security requirements
- Access approval workflows
- Vendor risk scoring
6. Regularly Test Cyber-Physical Incident Response
- Tabletop exercises
- Technical drills
- Joint IT-OT exercises
7. Perform Annual OT Cyber Maturity Assessments
- Based on ISA/IEC 62443
- Cover people, processes, technology
- Validate against threat intelligence
Conclusion
OT environments are mission-critical, safety-critical, and incredibly complex. While organizations may perform regular audits, there are hidden vulnerabilities that escape even the most structured assessment frameworks.
Cyber attackers-ransomware groups, nation-state actors, and criminal syndicates-are increasingly aware of these weak links. The result is a growing wave of attacks targeting industrial environments across manufacturing, utilities, transportation, energy, chemicals, and more.
By recognizing and addressing these 15 commonly missed OT security gaps, industrial organizations can significantly strengthen their cyber resilience, reduce operational risks, and protect the integrity of their critical infrastructure.