NIST SP 800-171 Rev. 3 3.15.3 — Rules of Behavior

What this control requires

This control requires establishing rules of behavior for system users, outlining their responsibilities and expected behavior for protecting Controlled Unclassified Information (CUI). It mandates providing these rules to users, obtaining their documented acknowledgment, and ensuring the rules are reviewed and updated regularly. This control supports the Rules of Behavior Management capability within the System and Information Integrity (3.15) family.

In plain English

This control requires establishing rules of behavior for system users, outlining their responsibilities and expected behavior for protecting Controlled Unclassified Information (CUI). In practice, this means you can prove you information management-level controls on a defined cadence.

Why it matters

DoD contractors and their subcontractors must implement all 100 SP 800-171 requirements to keep CUI handling contracts. Gaps are scored against the SPRS scoring methodology; below a 110-point starting score, each unmet requirement deducts points and a below-threshold score can disqualify a bid.

This control is rated high. Auditors expect a named owner, a remediation SLA, and a tooling artefact that evidences continuous operation.

What an auditor looks for

A C3PAO conducting a CMMC Level 2 assessment uses NIST SP 800-171A objectives. They expect a System Security Plan (SSP), Plan of Action & Milestones (POA&M) for any gaps, and objective evidence (configurations, ticket records, training records) for every requirement.

Within System and Information Integrity, the assessor will trace your implementation back to the catalogue reference (Requirement 3.15.3) and look for objective evidence on the latest two assessment cycles.

How to implement

Policy Management

Docs. Keep each policy in version-controlled Markdown alongside the code that implements it; ship a signed PDF snapshot at each annual review and link the SHA into the SoA.

Operational checklist

• Information. Document the trigger, the owner and the cadence.
• System. Document the trigger, the owner and the cadence.
• Risk. Document the trigger, the owner and the cadence.
• Policy. Document the trigger, the owner and the cadence.
• Rules. Document the trigger, the owner and the cadence.
• Scope: management, cui, behavior.

Evidence to collect

• Policy Document. A signed and version-controlled policy / standard / procedure document.
• Infra Scan. Continuous infrastructure-posture telemetry — AWS Config, Azure Policy compliance, GCP Organisation Policy, Wiz / Prisma findings.

Signed policy or standard documents the safeguard. Focus: Rules of Behavior.

Common pitfalls

• Policies that no engineer has read; the version in Confluence drifts from the version that's actually being enforced.

How it maps to other frameworks

Computed from shared tags, control component and key-operation subjects — handy when you are reconciling controls across an audit.

• ISO/IEC 27001:2022 A.5.5 — Contact with authorities
• SOC 2 (2017 TSC) CC2.3 — External Communication on Internal Control Matters
• HIPAA (45 CFR Part 164) 164.308(a)(5)(i) — Security Awareness and Training
• NIST SP 800-53 Rev. 5 SI-4(21) — Probationary Periods
• BSI C5:2020 SP-01 — Documentation, communication and provision of policies and instructions

Related controls in NIST SP 800-171 Rev. 3

• Requirement 3.15.1 — Policy and Procedures
• Requirement 3.13.11 — Cryptographic Protection
• Requirement 3.8.4 — Media Marking
• Requirement 3.10.6 — Alternate Work Site
• Requirement 3.13.15 — Session Authenticity
• Requirement 3.1.20 — Use of External Systems

References

• NIST Computer Security Resource Center — NIST SP 800-171 Rev. 3
• Catalogue identifier: Requirement 3.15.3

Topics: governance riskpolicy management