What is the Purpose of the ISOO CUI Registry?

 To work with the Department of Defense (DoD), organizations must follow strict guidelines for safeguarding Controlled Unclassified Information (CUI). A key part of this process is adhering to the ISOO CUI Registry, which provides standardized rules and definitions for handling CUI.

The ISOO CUI Registry helps organizations:

• Understand the purpose and scope of CUI
• Ensure stakeholders follow DoD Instruction 5200.48
• Implement security controls outlined in NIST SP 800-171
• Meet the CMMC requirements for DoD compliance

By following the ISOO CUI Registry, organizations can confidently align with DoD standards and protect sensitive information across all operations.

What is the Purpose of the ISOO CUI Registry?

The ISOO CUI Registry, maintained by the Information Security Oversight Office (ISOO), catalogs all document types considered Controlled Unclassified Information (CUI). Its primary purpose is to provide uniform definitions and responsibilities for handling CUI across all government agencies and their contractors. With few exceptions, everyone follows the same rules to ensure consistent protection of sensitive information.

For example, the first category in the ISOO CUI Registry is Critical Infrastructure, which includes CUI such as chemical terrorism vulnerability information and SAFETY Act data. All government entities and their contractors must mark and protect these documents according to the registry’s rules or face enforcement by ISOO or other authorities.

Additionally, the Department of Defense maintains its own DoD CUI Registry, which closely mirrors the ISOO version. The DoD registry covers all categories except Immigration and adds specific rules and responsibilities for DoD personnel and contractors.

Why is DoD Instruction 5200.48 Important?

DoD Instruction 5200.48 (DODI 5200.48) is the cornerstone of all Department of Defense guidance for safeguarding Controlled Unclassified Information (CUI). It establishes the infrastructure for the CUI program and outlines the key government departments responsible for reporting, oversight, and compliance. The instruction also clarifies the purposes and functions of CUI protection, providing practical rules and examples for organizations to follow.

One critical requirement under DODI 5200.48 is proper CUI marking. Organizations must use symbols or language on documents to indicate the type of information, who is authorized to access it, and which government entities control it. Accurate markings ensure that access and dissemination comply with regulatory standards.

For example:

• Documents marked “FEDCON” can be shared with both federal employees and contractors.
• Documents marked “FED ONLY” are restricted to federal employees and cannot be shared with contractors.

All personnel who handle CUI must be trained on these rules. Comprehensive training should include DODI 5200.48 in full, along with any supplemental guidance referenced within the instruction. This ensures that staff understand their responsibilities for protecting sensitive information under DoD standards.

How Does NIST SP 800-171 Protect CUI?

In addition to DODI 5200.48, organizations safeguarding Controlled Unclassified Information (CUI) must follow the NIST Special Publication 800-171 (NIST SP 800-171). This framework provides detailed programmatic guidance for network security controls, helping organizations reduce risks and protect sensitive data from cyber threats and vulnerabilities.

NIST SP 800-171 outlines 110 security requirements across 14 families:

1. Access Control – Managing who can access CUI and under what conditions
2. Awareness and Training – Educating staff on proper CUI handling
3. Audit and Accountability – Tracking and monitoring system activity
4. Configuration Management – Maintaining secure system configurations
5. Identification and Authentication – Verifying user identities
6. Incident Response – Detecting, reporting, and responding to security events
7. Maintenance – Securing system upkeep procedures
8. Media Protection – Safeguarding storage devices containing CUI
9. Personnel Security – Screening and managing personnel access to CUI
10. Physical Protection – Controlling physical access to systems and documents
11. Risk Assessment – Identifying and mitigating threats to CUI
12. Security Assessment – Evaluating security controls for effectiveness
13. System and Communications Protection – Securing network communications
14. System and Information Integrity – Ensuring system reliability and data accuracy

Implementing NIST SP 800-171 is also necessary to comply with the Defense Federal Acquisition Regulation Supplement (DFARS), which applies to nearly all DoD entities and contractors. Following these requirements ensures organizations are well-prepared to protect CUI and meet federal cybersecurity standards.

Is CMMC Required for CUI Protection?

While DODI 5200.48 and NIST SP 800-171 provide foundational guidance for safeguarding Controlled Unclassified Information (CUI), DoD contractors must also comply with the Cybersecurity Maturity Model Certification (CMMC). CMMC ensures that contractors have the proper security practices and controls in place to protect CUI and other sensitive data encountered when working with the U.S. Department of Defense.

DoD contracts require contractors to achieve a specific CMMC Level based on their exposure to CUI:

• Level 1: Foundational – Organizations with minimal CUI exposure must implement 15 practices from NIST SP 800-171 and complete annual self-assessments.
• Level 2: Advanced – Organizations with moderate CUI exposure must implement all 110 requirements from NIST SP 800-171 and undergo third-party assessments every three years.
• Level 3: Expert – Organizations with the highest CUI exposure must implement additional practices from NIST SP 800-172 and complete government-led triennial assessments.

By implementing the appropriate CMMC framework and completing the required assessments, organizations take the final step in meeting DoD guidance for safeguarding CUI. This ensures compliance and strengthens the organization’s overall cybersecurity posture.

What Level of System and Network Configuration is Required for CUI?

To properly safeguard Controlled Unclassified Information (CUI), organizations must implement a moderate level of system and network configuration. This includes:

• Securing network devices, servers, and endpoints that handle CUI

• Configuring firewalls, access controls, and authentication systems according to NIST SP 800-171 requirements

• Monitoring and maintaining system integrity to prevent unauthorized access or data breaches

• Ensuring secure communication channels for transmitting CUI

Adhering to these configuration standards helps organizations meet DoD compliance expectations and aligns with guidance from the ISOO CUI Registry, DODI 5200.48, and CMMC. Proper system and network configuration is a critical step in protecting sensitive government data and mitigating cybersecurity risks.

Protect CUI and Streamline DoD Compliance

In summary, safeguarding Controlled Unclassified Information (CUI) according to Department of Defense guidance requires a solid understanding of the ISOO CUI Registry, DoD CUI registry, DODI 5200.48, NIST SP 800-171, and CMMC. Each framework provides critical rules, requirements, and best practices to ensure sensitive information is properly protected.

Implementing these standards can be complex, but organizations can streamline compliance by training their workforce and collaborating with a DoD compliance advisor. This approach ensures that all personnel understand their responsibilities and that your organization maintains a strong, audit-ready posture for handling CUI.

Download Our CMMC Checklist