For defense contractors that handle Controlled Unclassified Information (CUI), implementing NIST SP 800-171 is not simply a matter of reading a cybersecurity framework and checking boxes. The real challenge is translating security requirements into everyday processes that employees, IT teams, managers, and outside service providers can consistently follow.

This can be particularly difficult for small and mid-sized companies in the Defense Industrial Base (DIB). These organizations often have limited cybersecurity staff, multiple operational priorities, and technology environments that have grown over time rather than being designed specifically around compliance.

NIST SP 800-171 establishes security requirements intended to protect the confidentiality of CUI in nonfederal systems and organizations. NIST published Revision 3 of the standard in May 2024, with updated requirements and a closer alignment to NIST SP 800-53.

Understanding the framework is important, but successful NIST 800-171 implementation depends just as much on how organizations manage scope, responsibilities, evidence, documentation, remediation, and ongoing changes.

Here are some of the most common challenges defense contractors encounter—and practical ways to address them.

Challenge 1: Not Knowing Where CUI Actually Lives

One of the biggest NIST 800-171 compliance problems begins before technical controls are even implemented.

Organizations may know they handle CUI but lack a clear picture of where that information is stored, processed, transmitted, or accessed.

CUI may exist in:

• employee laptops,
• shared drives,
• cloud platforms,
• email systems,
• engineering environments,
• collaboration applications,
• backups, or
• systems operated by external service providers.

NIST SP 800-171 applies to relevant nonfederal systems and system components that process, store, or transmit CUI or provide protection for those components.

How to Address It

Begin with data flow rather than technology.

Document how CUI enters the organization, who accesses it, where it moves, and where it eventually resides.

A clearer CUI environment makes security implementation far easier because the organization can define which systems, users, applications, and services actually require attention.

Without this step, companies may either leave important systems outside their compliance scope or unnecessarily expand the environment they are trying to secure.

Challenge 2: Treating NIST 800-171 as an IT-Only Responsibility

Another common mistake is giving the entire compliance program to the IT manager.

Technology teams certainly play an important role, but NIST 800-171 compliance includes far more than system configuration.

Security awareness training, personnel practices, physical protection, incident response, risk assessment, vendor management, policy development, and management oversight can involve several departments.

Revision 3 organizes its requirements across 17 security requirement families, demonstrating how broad the responsibility for protecting CUI can become.

How to Address It

Assign ownership at the requirement or workstream level.

For example:

IT may manage authentication and configuration.

Human resources may support personnel security and onboarding processes.

Management may approve cybersecurity policies.

Security teams may coordinate incident response and risk assessments.

External MSPs may operate certain technical safeguards.

The goal is not to build a large compliance department. It is to make sure every requirement has someone clearly responsible for maintaining it.

Challenge 3: Creating an SSP and Then Forgetting About It

The System Security Plan (SSP) is one of the most important documents in a defense contractor's cybersecurity environment, but it can quickly become outdated.

An SSP created today may describe the environment accurately. Six months later, the company may have migrated cloud services, added remote workers, changed security products, hired a new MSP, or redesigned part of its network.

If the documentation does not change with the technology, the organization eventually develops a gap between what its SSP says and what actually exists.

DFARS assessment requirements specifically incorporate review of the contractor's SSP when evaluating implementation of applicable NIST SP 800-171 requirements.

How to Address It

Treat the SSP as a living document.

Add a simple compliance question to change-management activities:

Does this change affect the SSP?

Whenever a major technology, process, location, service provider, or CUI workflow changes, review the relevant documentation.

Small updates throughout the year are easier than rebuilding the entire SSP immediately before an assessment.

Challenge 4: Evidence Is Scattered Everywhere

A security requirement may be implemented correctly but still become difficult to demonstrate if supporting evidence cannot be located.

Evidence often ends up spread across:

shared folders, ticketing platforms, employee computers, email conversations, security tools, training systems, screenshots, and spreadsheets.

During an assessment, the organization then has to reconstruct what happened and find proof that controls were operating.

NIST SP 800-171A provides assessment procedures designed to evaluate whether SP 800-171 security requirements are implemented.

How to Address It

Collect evidence when the security activity occurs.

When employees complete training, preserve the record.

When accounts are reviewed, retain evidence of the review.

When security configurations are changed, document the change.

When vulnerabilities are resolved, keep appropriate remediation evidence.

This turns NIST 800-171 evidence management into part of normal operations instead of a large project immediately before an assessment.

Challenge 5: Too Many Compliance Gaps at Once

Gap assessments often leave contractors with a long list of unfinished work.

The difficulty is not always identifying the gaps. It is deciding what to fix first.

Without prioritization, every issue may appear equally urgent, causing teams to jump between projects without completing the most important work.

How to Address It

Convert each gap into a specific remediation task.

Instead of writing:

“Improve access control,”

define:

“Review privileged accounts, remove unnecessary administrator access, document approval, and retain evidence.”

Assign an owner, expected completion date, dependencies, and evidence requirement.

Where formal Plans of Action and Milestones apply, DFARS assessment processes also recognize planned remediation information associated with outstanding security requirements.

Structured POA&M management helps turn cybersecurity deficiencies into work that teams can actually track and complete.

Challenge 6: Compliance Information Lives in Too Many Tools

Many defense contractors begin their compliance journey using spreadsheets.

That can work initially.

The difficulty comes when the organization needs to manage security requirements, gap assessments, SSP details, POA&Ms, evidence, policies, responsibilities, assets, and assessment information at the same time.

The problem becomes less about understanding cybersecurity and more about finding the latest information.

How to Address It

Create one reliable source of compliance information.

A centralized NIST 800-171 compliance software or cybersecurity compliance solution can help teams connect requirements, evidence, remediation activities, responsibilities, and documentation.

Centralization should make it easier to answer questions such as:

Which requirements are implemented?

Which gaps remain?

Who owns them?

What evidence supports implementation?

When was a requirement last reviewed?

The goal is not simply to digitize a spreadsheet. It is to create visibility across the compliance program.

Challenge 7: Confusion Around Revision 2, Revision 3, and CMMC

Defense contractors now face an additional challenge: understanding which version of NIST SP 800-171 they should be working against.

NIST SP 800-171 Revision 3 is the current NIST publication and was finalized in May 2024.

However, as of August 2026, the Department's current CMMC Phase I structure continues to enforce NIST SP 800-171 Revision 2 for applicable Level 2 self-assessments. The Department states that those assessments currently cover the 110 security requirements from Revision 2.

How to Address It

Do not assume that publication of a newer NIST revision automatically changes contractual obligations.

Contractors should determine which requirements are incorporated into their specific contracts and applicable assessment obligations.

At the same time, understanding Revision 3 is valuable because it represents the current direction of the NIST framework.

Organizations should therefore manage present contractual requirements while preparing intelligently for future transitions.

Challenge 8: Small Teams Simply Do Not Have Enough Time

For smaller defense suppliers, limited resources may be the biggest challenge of all.

The same employee responsible for NIST 800-171 may also manage endpoints, respond to support requests, administer cloud environments, communicate with vendors, and handle cybersecurity incidents.

NIST recognized this problem when it published SP 1318, a Small Business Primer designed specifically to help smaller and under-resourced organizations understand and begin implementing NIST SP 800-171 Revision 3.

How to Address It

Do not try to fix everything simultaneously.

Start with:

1. understanding the CUI environment,
2. assessing current implementation,
3. assigning ownership,
4. identifying high-priority gaps,
5. documenting remediation,
6. collecting evidence continuously, and
7. reviewing progress regularly.

A structured program reduces the cognitive burden on employees because everyone knows what needs to happen next.

Make NIST 800-171 a Manageable Business Process

The biggest NIST 800-171 implementation challenge is often not a particular security requirement.

It is lack of structure.

When scope is unclear, responsibilities are undefined, evidence is scattered, documentation is outdated, and remediation work is poorly tracked, compliance becomes overwhelming.

When those same activities are organized into repeatable workflows, the situation changes.

Defense contractors can make compliance easier by understanding where CUI exists, keeping their SSP current, assigning clear ownership, capturing evidence as work happens, tracking gaps systematically, and centralizing compliance information.

The objective should not be to complete NIST 800-171 once and move on.

The objective is to build a security program capable of protecting sensitive defense information consistently—even as employees, technology, contracts, and cybersecurity requirements continue to change.