---
title: "NIST 800-171 3.1.21 (AC.L2-3.1.21): Portable Storage Use"
description: "NIST SP 800-171 3.1.21 Portable Storage Use: 1 SPRS point, allowed on a CMMC POA&M. The text, what assessors check and the evidence."
url: https://policycortex.com/nist-800-171/access-control/3.1.21
sealed: 2026-11-11
amended: 2026-11-11
register: nist-800-171/access-control/3.1.21
records: 7
digest: sha3:167323b9744f13a607cea6d1162072b43c0c19e4a25798c4faa61633b890cf42
---

# NIST 800-171 3.1.21 (AC.L2-3.1.21): Portable Storage Use

NIST 800-171 / Access Control / 3.1.21

"Limit use of portable storage devices on external systems." ([NIST SP 800-171 Rev. 2, requirement 3.1.21](https://doi.org/10.6028/NIST.SP.800-171r2))

CMMC Level 2 practice AC.L2-3.1.21.

## What 3.1.21 means in practice

USB drives and other portable storage holding CUI should not be plugged into systems you do not control. Organizations usually either ban portable storage outright or allow only encrypted, company-issued drives under written conditions, and enforce the rule with device control on their own computers.

## SPRS points and the CMMC POA&M

- **CMMC Level 2 practice**: AC.L2-3.1.21
- **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](https://www.acq.osd.mil/asda/dpc/cp/cyber/docs/safeguarding/NIST-SP-800-171-Assessment-Methodology-Version-1.2.1-6.24.2020.pdf); [32 CFR 170.21, Plan of Action and Milestones requirements](https://www.ecfr.gov/current/title-32/section-170.21).

## What an assessor checks for 3.1.21

NIST SP 800-171A gives 3 determination statements for 3.1.21, each found satisfied or other than satisfied. Determine if:

- 3.1.21[a] the use of portable storage devices containing CUI on external systems is identified and documented.
- 3.1.21[b] limits on the use of portable storage devices containing CUI on external systems are defined.
- 3.1.21[c] the use of portable storage devices containing CUI on external systems is limited as defined.

[NIST SP 800-171A (June 2018), assessment objectives for 3.1.21](https://doi.org/10.6028/NIST.SP.800-171A)

## Evidence that shows 3.1.21 is met

- The written limits on using portable storage with external systems.
- Device control settings that block or restrict removable storage.
- A register of issued encrypted drives and their holders, where drives are allowed.

## How PolicyCortex gathers the evidence

PolicyCortex reads this evidence with the collectors below, read only, and grades 3.1.21 from it. Each line says what the product checks.

- **Microsoft Intune: Device configurations · Compliance policies.** Checks that removable storage is blocked on every laptop and desktop Intune manages.

## Related pages

- **Calculator**: [SPRS score calculator: mark 3.1.21 and the other 109 requirements and see the score.](https://policycortex.com/sprs-score-calculator#family-AC)
- **Sample package**: [Sample package: an SSP, a POA&M and an evidence chain the product generated from demonstration data.](https://policycortex.com/sample-package)
- **Family**: [All 22 Access Control requirements (3.1).](https://policycortex.com/nist-800-171/access-control)
- **Previous**: [3.1.20: External Connections](https://policycortex.com/nist-800-171/access-control/3.1.20)
- **Next**: [3.1.22: Public Information](https://policycortex.com/nist-800-171/access-control/3.1.22)
- **All requirements**: [All 110 NIST SP 800-171 requirements, by family.](https://policycortex.com/nist-800-171)

Meet the requirement once. Keep the evidence current. [Request Access](https://app.policycortex.com/auth?mode=request-access) · [Book a call](https://policycortex.com/book)

## Register colophon

| Seq | Label | SHA3-256 | Prev |
|---|---|---|---|
| REC 0000 | REQUIREMENT | 4a05db2cc5ab | ef28e0a04230 |
| REC 0001 | MEANING | 5e981fa6c4c6 | 4a05db2cc5ab |
| REC 0002 | POINTS AND POA&M | 14510013250e | 5e981fa6c4c6 |
| REC 0003 | ASSESSMENT OBJECTIVES | 0f8e9681375e | 14510013250e |
| REC 0004 | EVIDENCE | e5ba6c3acfc9 | 0f8e9681375e |
| REC 0005 | COLLECTORS | b0977b37ec67 | e5ba6c3acfc9 |
| REC 0006 | RELATED | 167323b9744f | b0977b37ec67 |

Head sha3:167323b9744f13a607cea6d1162072b43c0c19e4a25798c4faa61633b890cf42. Each digest is SHA3-256 over the previous digest, the register key, the record label, and the record copy; a second party can recompute it from this document.