IA-2(8): Access to Accounts — Replay Resistant

IA-2(8) requires you to use replay-resistant authentication for the systems and accounts in scope, so captured credentials (or authentication messages) can’t be reused to log in. Operationalize it by inventorying in-scope access paths, enforcing approved replay-resistant methods (for example FIDO2/WebAuthn or mutual TLS), and retaining configuration and test evidence that proves replay attacks would fail. ¹

Key takeaways:

• Define the scope first: which “access to accounts” paths are covered by your IA-2(8) parameter and architecture.
• Standard passwords alone do not satisfy replay resistance; require mechanisms with nonces/challenges, signed assertions, or equivalent protections.
• Evidence wins audits: configs, IdP policies, protocol settings, and replay test results mapped to systems and access methods.

The ia-2(8): access to accounts — replay resistant requirement is a narrow control enhancement with a broad blast radius because it touches every way a human or system authenticates. The assessor question behind IA-2(8) is simple: “If an attacker captures what was sent during login, can they replay it to get in?” If the answer is “yes” for any in-scope account access path, you have a control gap.

This requirement is usually implemented through modern authentication protocols and settings, not a standalone “policy.” In practice, you operationalize IA-2(8) by (1) stating what “access to accounts” means in your environment (the control parameter/scope), (2) enforcing replay-resistant mechanisms for each access channel (interactive, API, admin, remote), and (3) proving it with durable evidence tied to configurations and logs.

Teams often stumble because they treat “MFA exists” as sufficient. Some MFA patterns are replay-resistant; others can still be replayed (or can be downgraded). Your job as a CCO/GRC lead is to drive a crisp scope decision, insist on a standard pattern, and make evidence collection routine.

Regulatory text

Requirement (verbatim): “Implement replay-resistant authentication mechanisms for access to {{ insert: param, ia-02.08_odp }}.” ¹

What the operator must do:

1. Define the scope of “access to accounts” by setting the IA-2(8) parameter for your environment (the “{{ insert: param, ia-02.08_odp }}” part).
2. Implement authentication mechanisms that are replay-resistant for that scope, meaning the authentication exchange cannot be captured and reused successfully.
3. Maintain evidence that the mechanisms are enforced for the in-scope access paths. ¹

Plain-English interpretation (what “replay-resistant” means)

Replay resistance means an attacker can’t record an authentication message and reuse it later to authenticate. Typical replay-resistant designs use one or more of these properties:

• Challenge–response (a fresh nonce/challenge each time).
• Signed assertions bound to a session (assertion is unique and short-lived).
• Mutual authentication with channel binding (client and server prove identity in a way that can’t be reused out of context).

For most organizations, IA-2(8) becomes a requirement to standardize on approved authentication patterns for:

• Workforce interactive sign-in (SSO, privileged access, remote access).
• Service-to-service authentication (APIs, machine identities, workloads).
• Administrative access to systems that manage accounts or permissions.

Who it applies to (entity and operational context)

Entities: Federal information systems and contractor systems handling federal data commonly implement this requirement as part of NIST SP 800-53 control baselines. ²

Operational contexts where IA-2(8) typically applies:

• Identity providers (IdP) and SSO policies for workforce accounts.
• Privileged access paths (cloud consoles, hypervisors, directory admin, CI/CD admin).
• Remote access (VPN, ZTNA, VDI) where credential replay is a known attack path.
• APIs and integrations where tokens or signed requests must resist reuse.
• Third-party access into your environment (support portals, federated access, contractor logins) because replay risk crosses trust boundaries.

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

1) Set the IA-2(8) scope parameter (make it audit-grade)

Deliverable: A short scope statement that fills in “access to {{ insert: param, ia-02.08_odp }}.”
Do this as a written decision in your control narrative and SSP/control matrix, not a Slack message.

Practical scoping choices (examples you can adopt):

• “All interactive workforce access to enterprise accounts via SSO and all privileged administrative access.”
• “All access to accounts that can create, modify, or assign permissions.”
• “All access to cloud tenant administrative accounts and production break-glass accounts.”

Examiner hangup: If the scope is vague, assessors will assume it’s broad and sample aggressively.

2) Inventory account access paths and map them to auth methods

Create a table and keep it current. Minimum columns:

• System / application
• Account type (workforce, privileged, service)
• Access channel (web, SSH, API, console, VPN)
• Authentication mechanism in use (protocol + factor)
• Replay-resistant? (yes/no) with rationale
• Owner
• Evidence pointer (config, policy screenshot/export, log query)

This inventory becomes your control “spine.” Daydream can help you keep this mapping tied to owners and recurring evidence pulls so it doesn’t rot between audits. ¹

3) Define an approved replay-resistant standard (and ban weak patterns)

Write a one-page Authentication Standard that lists:

• Approved replay-resistant methods for interactive users (for example, phishing-resistant MFA based on challenge–response).
• Approved replay-resistant methods for services (for example, mutual TLS with managed certificates, or signed requests with nonces and strict expiry).
• Disallowed methods for in-scope access (for example, reusable static shared secrets by themselves, or long-lived bearer tokens without sender constraints).

Keep it narrow. Auditors want to see enforceable standards tied to configurations.

4) Implement controls by access channel

A. Workforce SSO / interactive logins

• Enforce the approved methods in the IdP conditional access policies.
• Block legacy auth flows that allow credential material to be replayed through older protocols.
• Require step-up authentication for admin portals and permission changes.

B. Privileged access

• Put privileged accounts behind your strongest replay-resistant method.
• If you use a PAM tool, validate the login flow for vault access is replay-resistant and that session establishment can’t be replayed.

C. APIs and service accounts

• Prefer short-lived, audience-restricted tokens and proof-of-possession patterns where supported.
• If using mTLS, enforce certificate issuance, rotation, and revocation controls and validate that the server requires client certs.

D. Third-party access

• For federated third-party identities, require your replay-resistant standard at the federation boundary (and enforce it through your IdP policies).
• For non-federated third parties, restrict them to managed access channels (VDI/portal) where you can enforce strong auth and log it.

5) Test replay resistance in a way you can show an assessor

You don’t need exotic tooling to prove the point. You need a repeatable test procedure:

• Capture an authentication request (or token) during a legitimate login in a controlled test environment.
• Attempt to reuse it after the challenge/nonce changes or after the session completes.
• Document that replay fails and record the system’s error behavior.

Artifact: A short test memo per major access pattern (SSO, VPN/ZTNA, API gateway, privileged console) with screenshots or logs.

6) Operationalize: monitoring, exceptions, and change control

• Monitoring: Alert on attempts that look like replay (duplicate assertions, repeated token IDs, repeated nonce failures where available).
• Exceptions: Create a time-bound exception process for systems that can’t meet replay resistance yet, with compensating controls and a migration plan.
• Change control: Make “replay-resistant auth preserved?” a required question in IAM and application change reviews.

Required evidence and artifacts to retain

Keep evidence that is configuration-based and traceable to scope:

• IA-2(8) scope statement (control narrative/SSP section). ¹
• Access-path inventory and mapping table with owners and dates.
• IdP configuration exports or screenshots showing enforced policies for in-scope apps/accounts.
• System configuration showing protocol settings (for example, mTLS required at ingress).
• Token/session configuration (TTL, audience restrictions) where relevant, captured as config evidence.
• Replay test procedure + results (dated, reviewer, environment).
• Exception register entries (business justification, compensating controls, expiry date, approval).

Common exam/audit questions and hangups

• “Define what ‘access to accounts’ includes in your environment. Which systems are in scope?” ¹
• “Show me where replay resistance is enforced in configuration, not just in policy.”
• “How do you prevent downgrade to non-replay-resistant flows?”
• “How do you know third-party access uses the same replay-resistant mechanisms?”
• “What is your evidence that captured authentication traffic cannot be reused?”

Assessors often sample your “weird paths”: break-glass accounts, legacy admin consoles, SFTP/SSH access, and integration service accounts.

Frequent implementation mistakes (and how to avoid them)

1. Calling any MFA “replay-resistant.”
   Fix: Define approved factors and protocols, then enforce them per app via IdP policy and technical controls.

2. Ignoring service-to-service paths.
   Fix: Treat workload identity as first-class scope. Include API gateways, message buses, and batch integrations in the inventory.

3. Relying on screenshots with no system mapping.
   Fix: Every screenshot/config export should point to a system, access path, and scope row in your inventory.

4. Allowing parallel legacy auth.
   Fix: Explicitly disable legacy protocols/flows for in-scope apps, and document the block with config evidence.

5. No exception discipline.
   Fix: Track exceptions with an end date and compensating controls, and review them on a defined cadence.

Risk implications (why auditors care)

Replay attacks turn “intercept once” into “access whenever.” The risk shows up as:

• Unauthorized account access without needing to crack passwords.
• Privileged session hijack leading to broad system compromise.
• Lateral movement through reused API credentials or tokens.
• Higher incident impact because replay often bypasses user awareness.

IA-2(8) is commonly tested indirectly: if an incident shows stolen tokens or captured auth traffic was reused, assessors will question whether replay resistance was real or only assumed.

Practical 30/60/90-day execution plan

First 30 days (stabilize scope and visibility)

• Write and approve the IA-2(8) scope statement tied to “access to accounts” in your environment. ¹
• Build the access-path inventory and identify the top risk paths: privileged access, remote access, IdP sign-in, API gateway.
• Define the approved replay-resistant authentication standard and disallowed methods.
• Stand up an exception register for anything that can’t meet the standard immediately.

Days 31–60 (enforce controls where you already have platforms)

• Implement IdP conditional access policy changes for in-scope apps and privileged roles.
• Remove or block legacy authentication flows for in-scope systems.
• Implement service authentication hardening (for example, mTLS at ingress or stronger token constraints where supported).
• Create the replay test procedure and run it for at least your primary interactive sign-in and your primary API pattern.

Days 61–90 (prove it and make it repeatable)

• Expand enforcement to remaining in-scope apps and third-party access paths.
• Add monitoring/alerting for suspicious authentication reuse patterns where your platforms expose signals.
• Convert evidence collection into a recurring routine: scheduled config exports, quarterly access-path inventory review, and replay test reruns after major auth changes.
• If you use Daydream, map IA-2(8) to a named control owner, a step-by-step procedure, and recurring evidence artifacts so your audit packet is always current. ¹

Frequently Asked Questions

Does MFA automatically satisfy IA-2(8)?

Only if the MFA method and protocol are replay-resistant for the in-scope access path. Document the specific mechanism and prove enforcement with IdP/system configuration evidence. ¹

What exactly counts as a “replay” in an audit discussion?

A replay is reusing captured authentication data (a request, assertion, token, or handshake material) to authenticate again. Your evidence should show fresh challenges/nonces, short-lived signed assertions, or equivalent controls that prevent reuse.

Is this only for workforce logins, or does it include APIs and service accounts?

IA-2(8) applies to “access to accounts” in your defined scope, which commonly includes service accounts and APIs. If you exclude them, document the scope decision and be ready to justify it to the assessor. ¹

How do I show replay resistance without doing a full penetration test?

Use a documented, repeatable replay test in a controlled environment plus configuration evidence that demonstrates challenge–response or session-bound assertions. Pair the test result with the exact system/policy settings used.

What should I do with legacy systems that can’t support replay-resistant authentication?

Put them in a time-bound exception with compensating controls (network restrictions, PAM jump access, strict monitoring) and a migration plan. Keep the exception register and approvals as part of your audit packet.

How should third-party access be handled under IA-2(8)?

Treat third-party identities and access channels as in-scope when they access your accounts or privileged functions. Require federation or managed access paths where you can enforce your replay-resistant standard and collect logs.

Footnotes

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

2. NIST SP 800-53 Rev. 5