Backup of PLC / HMI logic with restore tested
Demonstrate that PLC and HMI logic is systematically backed up, securely stored with version control, and that restoration procedures have been validated through documented testing to ensure operational recovery capability.
Description
What this control does
This control requires organizations to maintain current backup copies of Programmable Logic Controller (PLC) and Human-Machine Interface (HMI) logic, configuration files, and ladder logic programs, and to periodically test restoration procedures to verify recoverability. Backups must be versioned, stored securely offline or in separate network segments, and documented with metadata such as firmware versions, configuration dates, and system identifiers. Regular restore testing validates that backed-up logic can be successfully reloaded onto operational or test equipment without errors, ensuring operational continuity following equipment failure, ransomware attack, or malicious logic modification.
Control objective
What auditing this proves
Demonstrate that PLC and HMI logic is systematically backed up, securely stored with version control, and that restoration procedures have been validated through documented testing to ensure operational recovery capability.
Associated risks
Risks this control addresses
- Loss of critical industrial control logic following ransomware encryption or destructive malware attack, resulting in prolonged production outages
- Inability to restore operational state after accidental or malicious logic modification by unauthorized personnel or compromised engineering workstations
- Extended downtime due to equipment failure without accessible or functional backup copies of control programs and configurations
- Production of defective products or unsafe operating conditions following corrupted PLC logic that cannot be rolled back to known-good state
- Insider threat actors permanently deleting or modifying control logic without ability to forensically compare against baseline configurations
- Supply chain compromise introducing malicious logic modifications that go undetected without version-controlled baseline comparisons
- Compliance violations and regulatory penalties for failure to maintain recoverability controls in critical infrastructure environments
Testing procedure
How an auditor verifies this control
- Obtain and review the organization's backup policy and procedures specific to OT/ICS systems, identifying documented schedules, retention periods, storage locations, and restore testing requirements for PLC and HMI logic.
- Request an inventory of all PLCs and HMIs within scope, including manufacturer, model, firmware version, network location, and assigned backup responsibility.
- Select a representative sample of PLCs and HMIs across different control zones, criticality levels, and vendors for detailed examination.
- Inspect backup repositories (offline storage, secure network shares, or backup servers) and verify that current logic files exist for sampled devices with timestamps, version numbers, and metadata tags.
- Compare the firmware and configuration versions documented in backup metadata against live device configurations by reviewing engineering workstation exports or device interrogation logs.
- Review restore test records from the past 12 months, confirming that sampled devices or equivalent test equipment underwent successful restoration exercises with documented outcomes, timestamps, and personnel signatures.
- Interview engineering or OT personnel responsible for backup and restore activities to validate understanding of procedures, access controls to backup repositories, and escalation paths for restore failures.
- Examine change management records for any recent PLC or HMI logic modifications and verify that post-change backups were captured within the documented schedule requirements.
Where this control is tested