Managing Passwords on Hundreds of ICS Devices: Practical Strategies For Industrial Networks

Password management in Industrial Control System (ICS) environments has always been a vexing task, especially when faced with legacy hardware, firmware constraints, and the often merciless reality of field deployments spanning decades. This article aims to dissect practical approaches to password management at scale in these uniquely challenging environments, merging hard-won operational experience with open-eyed technical realism.

Historical Context: ICS Device and Password Realities

ICS devices—PLCs, RTUs, HMIs, protocol gateways, even smart relays—were never designed with security as a prime concern. Earlier generations (1980s-2000s) were engineered for robustness, uptime, and deterministic timing, with local physical security as a presumed perimeter. Password functionality was added slowly and unevenly; in some classic devices, it appeared almost as an afterthought.

Historical note: Many Modbus and DNP3 devices before the mid-2000s shipped with no password protection at all. When passwords did appear, they were static, weak, and rarely stored in ways that allowed for programmatic management. The concept of unique credentials per device was non-existent; a single sticky note could control an entire factory floor.

Modern Security Drivers: Why Password Lifecycle Management Became Impossible To Ignore

• Increase in remote operations: What had been local-only interfaces are now Internet- or WAN-accessible via IIoT, cloud, or centralized monitoring.

• Regulatory changes: Standards such as NERC CIP, IEC 62443, and NIST 800-82 explicitly demand password complexity/rotation and auditability.

• Real-world attacks: Incidents like BlackEnergy (Ukraine), the Triton attack, or generic ransomware have demonstrated how easily adversaries lateral-move via weak credential hygiene.

In summary, the old world of fixed passwords is no longer tenable for anyone who cares about operational continuity or regulatory compliance.

ICS Password Management: The Technical Realities

Device Constraints

• Limited Protocol Support: Many ICS devices only implement ICCP, Modbus, DNP3, or serial protocols that bear no concept of secure login. If password functionality exists at all, it's outside standard protocol mechanisms (often via vendor-specific tools).

• Lack of APIs: RESTful interfaces or remote provisioning APIs are rare. Passwords may live in NVRAM, EEPROM, or config files accessible only over serial or vendor USB interfaces.

• Downtime Risk: Changing passwords often requires brief downtime, reboots, or device resets, all of which are tightly controlled in high-availability processes.

• Credential Sharing: Historic use of shared password accounts (a "user" or "engineer" login for many devices) complicates both rotation and auditability.

Tiering: Not All Devices Are Equal

Start with a realistic device inventory and risk tiering process.

• Tier 1: Core Process Control Devices (PLCs, DCS Controllers) - High availability, firmware constraints, often no modern authentication mechanisms.

• Tier 2: OT Network Gear (managed switches, firewalls, protocol converters) - Usually better authentication, sometimes with TACACS+, RADIUS, or SSH keys.

• Tier 3: Site/Remote Access Gateways, HMIs, Engineering Workstations - Can be treated similarly to IT systems, often supporting PAM, Kerberos, Active Directory.

Fact: Attempting to apply modern IT password policies blindly to Tier 1/2 is a recipe for operator frustration and (possibly) operational risk. Prioritize Tier 3 for automation and Tier 1/2 for realistic, defendable compensating controls.

Strategies For Password Management At Scale

1. Centralized Password Vaults for Tier 2 and 3

• Leverage enterprise-class password managers (e.g., CyberArk, HashiCorp Vault, open source options) for anything with an API or SSH interface.

• For network gear, enable AAA via RADIUS/TACACS+ where possible. This centralizes identity and enables password rotation from the directory side with little device-specific configuration.

• Track all device accounts used by engineering staff—enforce unique credentials whenever possible (even if only one per technician) and tie vault access to user identity and session auditing.

2. Semi-Automated Bulk Updates (For Devices That Support It)

• If your vendor provides a scriptable CLI/tool (Schneider Electric EcoStruxure, Siemens TIA Portal for modern S7, Rockwell FactoryTalk), use it to write batch password update scripts, but test on non-production devices first—some tools do not handle partial failures gracefully.

• Where available, leverage SNMP (set commands), REST APIs, or configuration backups and restores (with new passwords baked in) to automate changes during maintenance windows.

Historical note: Automated password rotation is rarely reliable across multi-vendor brownfield environments. Accept "semi-automated" as a realistic goal.

3. Segmentation and Compensating Controls (When Direct Password Management Is Impossible)

• Enforce strong network segmentation between ICS zones and IT, or within ICS itself (cell/area), using firewalls or data diodes. If a device can only support static passwords, make sure its network context is tightly limited.

• Deploy jump hosts or bastion hosts with strong authentication and session logging as chokepoints for operator/engineer access, reducing the risk of credential leakage or misuse.

• Physical security and access auditing matter: if credentials can't be changed, be sure to log, badge, and camera-monitor physical access zones.

4. Vendor Engagement and Retrofit Strategies

• Push vendors (especially if maintaining support contracts) to provide firmware updates with modern authentication and password management. This is a years-long process, but critical for future projects.

• On particularly critical legacy assets, consider front-ending insecure devices with protocol-aware security gateways or “bump-in-the-wire” appliances that enforce per-session credentials even when the downstream device does not.

IT/OT Collaboration: Bridging the Cultural Divide

IT security teams often expect perfect control and fast changes; OT engineers live in a world where a three-minute reboot for a password change might incur a million-dollar process risk. Both sides must align:

• Jointly define password policies—complexity, rotation intervals, session audit requirements—by asset tier. Accept deviations for ICS-resident devices, but mitigate via network, logging, or physical controls.

• Clarify who is responsible for credential changes—Control staff? IT Security? A new hybrid Security Operations Center team with plant clearances?

• Practice transparency—keep device inventory, password rotation logs, and exception justifications in joint documentation, not "tribal knowledge" or emails.

Securely Deploying Connectivity: Treat Passwords as Just One Layer

Every password (or lack thereof) needs to be architected alongside encrypted transport (VPN, TLS, or at least SSH), robust network segmentation, and multi-factor authentication for any remote access portals.

Annotation: A well-segmented architecture can dramatically reduce the exposure of devices with weak or infrequently changed passwords, buying time until technical or operational upgrades are possible.

Pragmatic Password Rotation Guidelines

• Aim for annual rotation on Tier 1 ICS devices, with emergency forced change upon staff departure or suspected compromise. Accept this is not "every 90 days." Favor operational stability.

• Enforce quarterly to monthly rotation for Tier 2/3 (network/endpoint) systems where tooling permits it, tying access to named user accounts and session logging.

• Hold a standing "exceptions register" for all devices where password updates are technically impossible, and revisit it with each hardware/software refresh cycle.

Conclusion: The Real Path Forward

You will not—cannot—bring brownfield ICS into line with NIST, CIS, or ISO frameworks if your plan involves treating every device like a Windows server. Compensating controls, risk-based inventory, and honest documentation of technical limitations are not signs of failure—they are the marks of a mature security program in the real world.

Push where possible (implement scripts, vaults, semi-automation, and network AAA), contain where necessary (segmentation, jump hosts), and document everywhere. Engage operations teams early, recognize limitations, and avoid the fantasy that “compliance” can be attained with a single tool or policy.

Further Reading & Resources

• ISA/IEC 62443-2-1:2018 - Security Program Requirements for IACS Asset Owners

• NIST SP 800-82 Rev. 3 - Guide to Industrial Control Systems (ICS) Security

• SANS Whitepaper: ICS Password Practices – What Actually Works?

• CISA: Recommended Practices for Password Policies in Industrial Environments

A Final Note

Treat password management not as a sprint to some mythical “zero default passwords” finish line, but as an ongoing process rooted in the unique technical, operational, and cultural fabric of your industrial environment. No silver bullets—just honest, practical engineering.