---
title: "NIST 800-171 3.5.5 (IA.L2-3.5.5): Identifier Reuse"
description: "NIST SP 800-171 3.5.5 Identifier Reuse: 1 SPRS point, allowed on a CMMC POA&M. The text, what assessors check and the evidence."
url: https://policycortex.com/nist-800-171/identification-and-authentication/3.5.5
sealed: 2026-11-11
amended: 2026-11-11
register: nist-800-171/identification-and-authentication/3.5.5
records: 7
digest: sha3:8a82d6c8b9de6923b58bc3a8fde08d6dd9d64d4cf3bbe6fc8b51debacad3e626
---

# NIST 800-171 3.5.5 (IA.L2-3.5.5): Identifier Reuse

NIST 800-171 / Identification and Authentication / 3.5.5

"Prevent reuse of identifiers for a defined period." ([NIST SP 800-171 Rev. 2, requirement 3.5.5](https://doi.org/10.6028/NIST.SP.800-171r2))

CMMC Level 2 practice IA.L2-3.5.5.

## What 3.5.5 means in practice

Once a username or other identifier has been assigned, it is not handed to someone else for a defined period, so old permissions, records and audit trails never attach to the wrong person. Define the period and make the account process enforce it.

## SPRS points and the CMMC POA&M

- **CMMC Level 2 practice**: IA.L2-3.5.5
- **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 3.5.5

NIST SP 800-171A gives 2 determination statements for 3.5.5, each found satisfied or other than satisfied. Determine if:

- 3.5.5[a] a period within which identifiers cannot be reused is defined.
- 3.5.5[b] reuse of identifiers is prevented within the defined period.

[NIST SP 800-171A (June 2018), assessment objectives for 3.5.5](https://doi.org/10.6028/NIST.SP.800-171A)

## Evidence that shows 3.5.5 is met

- The defined period during which identifiers cannot be reused.
- The account creation procedure or tool setting that checks for earlier use.
- A sample of recent accounts showing no reused identifiers.

## How PolicyCortex gathers the evidence

No PolicyCortex collector reads the evidence for 3.5.5. Your team provides the evidence listed above.

## Related pages

- **Calculator**: [SPRS score calculator: mark 3.5.5 and the other 109 requirements and see the score.](https://policycortex.com/sprs-score-calculator#family-IA)
- **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 11 Identification and Authentication requirements (3.5).](https://policycortex.com/nist-800-171/identification-and-authentication)
- **Previous**: [3.5.4: Replay Resistance](https://policycortex.com/nist-800-171/identification-and-authentication/3.5.4)
- **Next**: [3.5.6: Inactive Accounts](https://policycortex.com/nist-800-171/identification-and-authentication/3.5.6)
- **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 | 5fc1656319d3 | 8ea3a3a25d0b |
| REC 0001 | MEANING | 1b33fc0c2321 | 5fc1656319d3 |
| REC 0002 | POINTS AND POA&M | b8ee4c8cd332 | 1b33fc0c2321 |
| REC 0003 | ASSESSMENT OBJECTIVES | 8a22ffef7e23 | b8ee4c8cd332 |
| REC 0004 | EVIDENCE | bb57e2a5517b | 8a22ffef7e23 |
| REC 0005 | COLLECTORS | e67606f4236e | bb57e2a5517b |
| REC 0006 | RELATED | 8a82d6c8b9de | e67606f4236e |

Head sha3:8a82d6c8b9de6923b58bc3a8fde08d6dd9d64d4cf3bbe6fc8b51debacad3e626. 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.