NIST SP 800-171 Rev. 3 3.13.15 — Session Authenticity

What this control requires

This control requires protecting the authenticity of communication sessions to ensure that both parties' identities are verified and that transmitted information remains valid. It aims to prevent adversary-in-the-middle attacks, session hijacking, and the insertion of false information into sessions. This control supports the Session Authenticity Protection capability within the Situational Awareness (3.13) family.

In plain English

This control requires protecting the authenticity of communication sessions to ensure that both parties' identities are verified and that transmitted information remains valid. 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 Situational Awareness, the assessor will trace your implementation back to the catalogue reference (Requirement 3.13.15) 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.
• Session. Document the trigger, the owner and the cadence.
• Protection. 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.
• Scope: management, protection, authenticity.

Evidence to collect

• Policy Document. A signed and version-controlled policy / standard / procedure document.

Signed policy or standard documents the safeguard. Focus: Session Authenticity.

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 PL-6 — Security-Related Activity Planning
• BSI C5:2020 AM-06 — Asset Classification and Labelling

Related controls in NIST SP 800-171 Rev. 3

• Requirement 3.13.11 — Cryptographic Protection
• Requirement 3.13.10 — Cryptographic Key Establishment and Management
• Requirement 3.14.3 — Security Alerts, Advisories, and Directives
• Requirement 3.13.2 — Recategorized as NCO
• Requirement 3.15.1 — Policy and Procedures
• Requirement 3.8.4 — Media Marking

References

• NIST Computer Security Resource Center — NIST SP 800-171 Rev. 3
• Catalogue identifier: Requirement 3.13.15

Topics: governance riskpolicy management