IA-2(9): Network Access to Non-privileged Accounts — Replay Resistant

IA-2(9) is a requirement-level control enhancement that forces a specific outcome: if someone steals authentication traffic or tokens, they still cannot replay them to gain network access as a normal user. This is easy to misunderstand because many programs focus replay resistance only for privileged access, VPN, or “high-risk” applications. IA-2(9) removes that ambiguity for systems aligned to NIST SP 800-53 by explicitly targeting network access and explicitly including non-privileged accounts. ¹

For a Compliance Officer, CCO, or GRC lead, the fastest path to operationalizing IA-2(9) is to treat it like a narrow engineering deliverable with measurable checkpoints: identify which access paths qualify as “network access,” enumerate the authentication mechanisms on those paths, confirm replay-resistant properties, and lock evidence collection into your operating rhythm. The most common failure mode is “we have MFA” without validating whether the factor and protocol are replay resistant in the way the control expects (for example, MFA prompts that can be phished and replayed, or legacy protocols that expose reusable secrets). Your job is to drive crisp scope, clear technical requirements, and audit-ready artifacts.

Requirement: IA-2(9) network access to non-privileged accounts — replay resistant

Objective: For network access by non-privileged users, require authentication that is replay resistant, so captured authentication data cannot be reused to authenticate. ¹

Plain-English interpretation

“Replay resistant” means an attacker should not be able to:

• record a login exchange (or steal a token/OTP), then
• submit the same captured material later, and
• successfully authenticate.

In practice, replay resistance usually comes from challenge-response properties, cryptographic binding, short-lived and audience-bound tokens, and protocols designed to prevent reuse of captured credentials.

Who it applies to

Entity types (typical):

• Federal information systems
• Contractor systems handling federal data ¹

Operational context (where you should scope it):

• Remote access into your environment (VPN/ZTNA)
• Workforce identity providers used for network sign-in flows
• Virtual desktops and bastions used by standard users
• Network services accessed directly by end users (common examples include SMB shares, internal web apps behind a reverse proxy, Wi‑Fi with enterprise authentication, and any environment where “network access” is the gating step)

Account scope:

• “Non-privileged” means standard user accounts without elevated administrative permissions. Treat “power users” and local admins carefully; if they can administer systems, they may fall outside “non-privileged” and into privileged requirements, but you still need replay resistance for the non-privileged population. ¹

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Regulatory text

Regulatory excerpt: “NIST SP 800-53 control IA-2.9.” ¹

Operator meaning: You must implement replay-resistant authentication for network access by non-privileged accounts, then be able to demonstrate (a) what access paths are in scope, (b) what mechanisms enforce replay resistance, and (c) how you verify the control keeps working.

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What you actually need to do (step-by-step)

1) Define “network access” for your environment (scope statement)

Create a short scoping memo (one page) that lists the network entry points and protocols that constitute “network access” in your architecture. Examples of scoping decisions you must make:

• Does “network access” include direct access to internal apps via SSO? Often yes, if the app is the gateway to internal network resources.
• Does it include Wi‑Fi authentication? Often yes, for enterprise Wi‑Fi used to access internal resources.
• Does it include SSH/RDP to endpoints? Often yes, where used broadly by standard users.

Deliverable: IA-2(9) scope statement + in-scope system list.

2) Inventory non-privileged authentication flows on those access paths

For each access path, document:

• authenticator type(s): password, OTP, push, FIDO2/WebAuthn, client certs, Kerberos, SAML/OIDC tokens, etc.
• where MFA is enforced (IdP, VPN, ZTNA, OS login, RADIUS/NPS)
• whether legacy protocols bypass MFA (common gap: “some apps still allow basic auth”)

Deliverable: Access-path matrix (table) mapping entry point → identity source → authenticator → enforcement point.

3) Decide what “replay resistant” means in your technical standard

Write an internal technical standard that states approved replay-resistant mechanisms for network access. Keep it short and testable.

A practical way to structure the standard:

Access type	Approved replay-resistant methods	Disallowed patterns (examples)
Workforce remote network access	Phishing-resistant MFA (for example, FIDO2/WebAuthn) or equivalent replay-resistant methods	Reusable passwords alone; OTP codes that can be captured and replayed; sessions not bound to user/device context
Token-based SSO for network entry	Short-lived tokens with appropriate binding/validation at the gateway	Long-lived bearer tokens copied from a browser and replayed without additional binding

Don’t over-promise. If you cannot yet move to phishing-resistant MFA everywhere, define an interim standard that is still replay resistant for the specific access path (and document compensating controls and a migration plan).

Deliverable: “Replay-Resistant Network Authentication Standard” (approved by security engineering and GRC).

4) Implement enforcement at the right control points

Common enforcement points:

• Identity provider conditional access (force compliant MFA methods for defined apps/network gateways)
• VPN/ZTNA policy (require strong MFA; block legacy auth; enforce device posture if used)
• RADIUS/NPS for Wi‑Fi (tie enterprise auth to the IdP with strong MFA where supported)
• Reverse proxy/access gateway in front of internal web apps

Implementation checks you can assign to engineering:

• Confirm the selected method cannot be replayed by simply re-submitting captured data.
• Disable or restrict fallback methods that weaken replay resistance (for example, “allow SMS fallback for all users”).
• Ensure session/token lifetimes and renewal flows align to your replay-resistance goal (short-lived, validated, and not trivially reusable).

Deliverable: Configuration changes + change tickets + peer review notes.

5) Validate with adversarial thinking, not just “MFA enabled”

You need at least one validation activity that is understandable to an auditor:

• Demonstrate that captured credentials/tokens from a login attempt cannot be reused to authenticate again.
• Show that the network entry point rejects legacy or weaker methods for the in-scope user group.

This can be a documented internal test, a red-team exercise excerpt, or a controlled replay attempt in a test environment. Keep it reproducible.

Deliverable: Test plan + results + remediation records where failures were found.

6) Operationalize: monitoring, drift detection, and exceptions

Replay resistance breaks over time when teams add exceptions. Build controls around change:

• Monitor conditional access/MFA policy changes.
• Alert on enabling legacy protocols or bypass groups.
• Require time-bounded exceptions with business owner sign-off and compensating controls.

Deliverable: Exception register entries + monitoring rules + periodic access path review.

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Required evidence and artifacts to retain

Auditors typically want proof that replay resistance exists on the wire and in enforcement logic, not just in a policy binder. Build an evidence set you can refresh each review cycle:

1. Scope statement listing in-scope network access paths and user populations.
2. Access-path matrix mapping network entry points to authenticators and enforcement points.
3. Configuration exports/screenshots:
   • IdP conditional access policies
   • VPN/ZTNA auth policies
   • RADIUS/NPS policies (if used)
   • Gateway/proxy settings for internal apps
4. Protocol and method restrictions documentation (what’s blocked and how).
5. Test evidence demonstrating replay attempts fail (test case + output).
6. Exception register with approvals and expiration dates.
7. Change records showing review/approval for auth-policy changes.

Daydream (as a GRC system of record) fits best here as the place you map IA-2(9) to a control owner, link each access path to evidence artifacts, and run recurring evidence tasks so you don’t rebuild proof during an assessment.

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Common exam/audit questions and hangups

Expect questions like:

• “Show me which network access paths are covered for standard users, and how you know you found them all.”
• “Where is replay resistance enforced: IdP, VPN, gateway, endpoint? Show the config.”
• “Do any users have MFA bypass groups? Who approves them? When do they expire?”
• “Are any legacy protocols enabled that permit non-replay-resistant authentication?”
• “How do you validate this control continues to operate after changes?”

Hangup to avoid: auditors get stuck when teams conflate MFA presence with replay resistance. Your evidence must connect “this method” to “cannot be replayed” through configuration and test.

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Frequent implementation mistakes and how to avoid them

1. Mistake: Treating IA-2(9) as “privileged access only.”
   Fix: explicitly list non-privileged user groups and apply the policy to them.

2. Mistake: Allowing fallback factors that are replayable.
   Fix: define allowed methods for network entry points and restrict the rest with conditional access.

3. Mistake: Missing “shadow” access paths.
   Fix: inventory VPN, Wi‑Fi, VDI, legacy remote tools, and direct-to-service protocols; tie each to the matrix.

4. Mistake: Evidence is screenshots from one day with no change history.
   Fix: retain configuration exports and change approvals, and schedule recurring evidence capture.

5. Mistake: Exceptions become permanent.
   Fix: require expirations, compensating controls, and periodic review.

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Enforcement context and risk implications

No public enforcement cases were provided for this specific enhancement in the supplied source set. The practical risk remains straightforward: replayable authentication is a common entry point for account takeover, lateral movement, and persistence. For federal and federal-adjacent environments, failing IA-2(9) usually shows up as an assessment finding because you cannot prove the authentication method resists replay for standard user network access. ²

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A practical 30/60/90-day execution plan

First 30 days (Immediate)

• Assign a control owner and technical owner for IA-2(9). ¹
• Publish the IA-2(9) scope statement (network access paths + non-privileged user definition).
• Build the access-path matrix and identify the highest-risk gaps (bypass groups, legacy auth, inconsistent MFA).

By 60 days (Near-term)

• Approve and roll out the replay-resistant network authentication standard.
• Implement enforcement for the highest-impact entry points (IdP conditional access, VPN/ZTNA, core gateways).
• Stand up the exception process with expirations and required compensating controls.

By 90 days (Operationalize)

• Run and document replay-resistance validation tests for each in-scope access path.
• Establish monitoring for policy drift and legacy auth enablement.
• Convert the evidence set into recurring tasks (owner, frequency, storage location) in Daydream or your existing GRC workflow so the next assessment is routine.

Frequently Asked Questions

Does IA-2(9) require MFA for every non-privileged user login?

IA-2(9) requires replay-resistant authentication for network access by non-privileged accounts. MFA is a common way to meet it, but the key test is replay resistance for the in-scope network entry points. ¹

Is push-based MFA replay resistant?

It depends on the implementation and the attack model your assessors apply. Treat “MFA enabled” as insufficient; document why your chosen method is replay resistant for the specific access flow and retain test evidence that replay attempts fail.

Are short-lived OTP codes replay resistant?

OTPs reduce risk but can still be captured and replayed within their validity window in some scenarios. If you rely on OTP for IA-2(9), document why it meets replay-resistance expectations for your network access paths and restrict higher-risk fallbacks.

What counts as “network access” in a cloud-first environment?

Treat the identity gateway to internal resources as “network access,” including ZTNA, VPN, and access proxies in front of internal apps. Document your boundary decision in the IA-2(9) scope statement so auditors can follow your logic. ¹

How do we handle third-party access for contractors with standard accounts?

If third parties receive non-privileged accounts that grant network access, include those flows in scope and enforce replay-resistant methods the same way. Track exceptions contractually and operationally via an exception register and offboarding process.

What evidence is most persuasive to an auditor?

Configuration exports of the enforcement policies, a clear access-path matrix, and a reproducible validation test that demonstrates a captured authentication artifact cannot be reused. Pair that with change records to show the control remains in place over time.

Footnotes

1. NIST SP 800-53 Rev. 5 OSCAL JSON

2. NIST SP 800-53 Rev. 5