NIST 800-171 3.1.3 (AC.L2-3.1.3): CUI Flow Control

Control the flow of CUI in accordance with approved authorizations.

NIST SP 800-171 Rev. 2, requirement 3.1.3

CMMC Level 2 practice AC.L2-3.1.3Published 2026-11-11

What 3.1.3 means in practice

This requirement is about where CUI may travel, not who may read it. Decide which networks, systems, people and services CUI may move between, then enforce those routes with firewalls, network rules, proxies or data loss prevention, so CUI cannot leave the approved paths by accident.

SPRS points and the CMMC POA&M

CMMC Level 2 practice: AC.L2-3.1.3
SPRS points: 1 point. When it is not met, the DoD Assessment Methodology subtracts 1 from the score of 110.
CMMC POA&M: Allowed. It is worth 1 point, and 32 CFR 170.21(a)(2)(ii) admits requirements worth 1 point. Conditional status also needs a score of at least 88, and the item must be closed within 180 days.

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 3.1.3

NIST SP 800-171A gives 5 determination statements for 3.1.3, each found satisfied or other than satisfied. Determine if:

3.1.3[a] information flow control policies are defined.
3.1.3[b] methods and enforcement mechanisms for controlling the flow of CUI are defined.
3.1.3[c] designated sources and destinations (e.g., networks, individuals, and devices) for CUI within the system and between interconnected systems are identified.
3.1.3[d] authorizations for controlling the flow of CUI are defined.
3.1.3[e] approved authorizations for controlling the flow of CUI are enforced.

NIST SP 800-171A (June 2018), assessment objectives for 3.1.3

Evidence that shows 3.1.3 is met

A data flow diagram showing where CUI enters, moves within and leaves the system boundary.
The written information flow policy naming approved sources and destinations for CUI.
Firewall, network security group or proxy rules that enforce those routes.
Data loss prevention or mail gateway rules that stop CUI from reaching unapproved destinations.

How PolicyCortex gathers the evidence

PolicyCortex reads this evidence with the collectors below, read only, and grades 3.1.3 from it. Each line says what the product checks.

Azure: Network security groups. Checks that network security group rules control the network traffic that can flow between enclaves.
AWS: EC2 and VPC networking. Checks that security groups restrict SSH and common ports from the internet and that each VPC's default security group has no rules.
AWS: S3 buckets. Checks that no S3 bucket is publicly readable or publicly writable.

Related pages

Calculator: SPRS score calculator: mark 3.1.3 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 22 Access Control requirements (3.1).
Previous: 3.1.2: Transaction Control
Next: 3.1.4: Separation of Duties
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.