NIST 800-171 3.13.15 (SC.L2-3.13.15): Session Authenticity

Protect the authenticity of communications sessions.

NIST SP 800-171 Rev. 2, requirement 3.13.15

CMMC Level 2 practice SC.L2-3.13.15Published 2026-11-11

What 3.13.15 means in practice

Communications sessions are protected against hijacking and man-in-the-middle attacks, so each side knows it is still talking to the right party. TLS with valid certificates, signed tokens and secure session handling in applications are the common protections.

SPRS points and the CMMC POA&M

CMMC Level 2 practice: SC.L2-3.13.15
SPRS points: 5 points. When it is not met, the DoD Assessment Methodology subtracts 5 from the score of 110.
CMMC POA&M: Not allowed. It is worth 5 points, and 32 CFR 170.21(a)(2)(ii) admits only requirements worth 1 point, with one exception: 3.13.11 when encryption is used but not FIPS validated.

Sources: NIST SP 800-171 DoD Assessment Methodology, version 1.2.1 (June 24, 2020), Annex A; 32 CFR 170.21, Plan of Action and Milestones requirements.

What an assessor checks for 3.13.15

NIST SP 800-171A gives one determination statement for 3.13.15.

Determine if the authenticity of communications sessions is protected.

NIST SP 800-171A (June 2018), assessment objectives for 3.13.15

Evidence that shows 3.13.15 is met

TLS configuration and certificates for applications and services.
Application session management settings, such as secure, short-lived session tokens.
Results of a web application scan or test that covered session handling.

How PolicyCortex gathers the evidence

PolicyCortex reads this evidence with the collectors below, read only, and grades 3.13.15 from it. Each line says what the product checks.

Azure App Service: App settings. Checks that App Service communications sessions are protected with TLS.

Related pages

Calculator: SPRS score calculator: mark 3.13.15 and the other 109 requirements and see the score.
Sample package: Sample package: an SSP, a POA&M and an evidence chain the product generated from demonstration data.
Family: All 16 System and Communications Protection requirements (3.13).
Previous: 3.13.14: Voice over IP
Next: 3.13.16: CUI at Rest
All requirements: All 110 NIST SP 800-171 requirements, by family.

Related records

Guides and articles describe the work. The evidence that work produces is described in three proof pages, the architecture page, and the two pages on authorization.

proof.state: Proof of State. What the environment was, as of a date someone else picks: point-in-time records, content hashed and chained.
proof.change: Proof of Change. Who or what altered the environment, under what authority, with before and after state hashes.
proof.agency: Proof of Agency. What a machine was permitted to do before it acted, what it did, and what would have stopped it.
architecture: Architecture. How the chain is built and where the evidence is stored in each delivery mode.
authorization: Continuous ATO. How an authorizing official's decision is recorded with its package, and how the authorized system is checked against it every hour.
baseline: NIST SP 800-53. The Low, Moderate and High baselines as evidence, with the SSP, SAR and POA&M generated from one record.