NIST 800-171 3.5.5 (IA.L2-3.5.5): Identifier Reuse
Prevent reuse of identifiers for a defined period.
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; 32 CFR 170.21, Plan of Action and Milestones requirements.
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
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.
Meet the requirement once. Keep the evidence current.
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