NIST 800-171 3.5.4 (IA.L2-3.5.4): Replay Resistance

Employ replay-resistant authentication mechanisms for network access to privileged and non-privileged accounts.

NIST SP 800-171 Rev. 2, requirement 3.5.4

CMMC Level 2 practice IA.L2-3.5.4Published 2026-11-11

What 3.5.4 means in practice

A captured sign-in must not be reusable by whoever captured it. Authentication built on one-time codes, challenge and response, or cryptographic tokens (such as Kerberos, FIDO2 security keys or authenticator apps) resists replay; protocols that send a reusable password or hash, like basic authentication, do not.

SPRS points and the CMMC POA&M

CMMC Level 2 practice: IA.L2-3.5.4
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 3.5.4

NIST SP 800-171A gives one determination statement for 3.5.4.

Determine if replay-resistant authentication mechanisms are implemented for network account access to privileged and non-privileged accounts.

NIST SP 800-171A (June 2018), assessment objectives for 3.5.4

Evidence that shows 3.5.4 is met

The authentication protocols allowed for network access, and the legacy ones disabled.
Identity provider settings for the factors in use, such as FIDO2 security keys or authenticator apps.
VPN and network device authentication settings.

How PolicyCortex gathers the evidence

PolicyCortex reads this evidence with the collectors below, read only, and grades 3.5.4 from it. Each line says what the product checks.

Microsoft Entra ID: Conditional Access. Checks that Conditional Access requires a replay-resistant factor for network sign-ins by every user and by privileged accounts.
Microsoft Entra ID: Authentication methods. Reads the Microsoft Entra authentication methods policy and reports whether FIDO2 security keys and certificate-based authentication are turned on.
Okta: Policies. Checks that Okta sign-ins require a replay-resistant second factor.

Related pages

Calculator: SPRS score calculator: mark 3.5.4 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 11 Identification and Authentication requirements (3.5).
Previous: 3.5.3: Multifactor Authentication
Next: 3.5.5: Identifier Reuse
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.