CMMC Level 2 Practice 3.5.8: Prohibit password reuse for a specified number of generations

To meet cmmc level 2 practice 3.5.8: prohibit password reuse for a specified number of generations requirement, you must configure every in-scope authentication system to block users from reusing recent passwords and document the exact “password history” value you enforce. Then you must prove it operates consistently across CUI-scoped identities, including exceptions, service accounts, and any federated identity paths.

Key takeaways:

• Set and document a password history value (“generations”) and enforce it technically, not by policy alone. ¹
• Scope matters: apply the control to all accounts that can access CUI environments, including cloud identity providers and remote access. ²
• Evidence wins assessments: keep configuration exports, test results, and exception approvals mapped to your CMMC/NIST control narrative. ²

CMMC Level 2 expects you to implement NIST SP 800-171 Rev. 2 practices for protecting Controlled Unclassified Information (CUI) in contractor environments. Practice 3.5.8 is a narrow control with a familiar goal: stop users from cycling back to old passwords. The operational trap is that “we have a password policy” is not the same as “the system prevents reuse,” and assessors will look for technical enforcement plus durable evidence.

This requirement is also easy to partially implement. Teams often configure password history in one directory (for example, on-prem AD) while overlooking a cloud identity provider, a VPN/remote access portal, local workstation accounts, or privileged access tooling. Another common gap is service and shared accounts that bypass normal password-change flows.

This page gives you requirement-level implementation guidance you can execute quickly: scoping decisions, configuration steps, exception handling, and the evidence package you’ll want ready for a CMMC Level 2 assessment. It is written for operators who need a “do this, keep that” checklist tied back to the CMMC/NIST practice language. ²

Requirement: CMMC Level 2 Practice 3.5.8 password reuse prohibition (generations)

Objective: Prevent users from reusing recent passwords by enforcing a password history value (“specified number of generations”) in the systems that perform authentication for your CUI environment. ¹

Plain-English interpretation

You must pick a password history value (the number of previous passwords the system remembers) and configure your identity systems so users cannot set a new password that matches any password in that remembered history. Document the value and prove enforcement works. ¹

This is a technical control first. Policy language supports it, but policy alone does not satisfy “prohibit.” In practice, assessors expect to see:

• a stated “password history” requirement in your access control/authentication standards, and
• system configurations that enforce it for in-scope identities. ²

Regulatory text

Framework mapping excerpt: “CMMC Level 2 practice mapped to NIST SP 800-171 Rev. 2 requirement 3.5.8 (Prohibit password reuse for a specified number of generations).” ¹

What the operator must do

1. Specify the password reuse window (your chosen “generations” value) in your documented standard for accounts that access CUI systems. ¹
2. Configure enforcement in each authentication authority that can authenticate those accounts (directory services, identity provider, SSO, VPN, PAM, and local account stores where applicable). ²
3. Verify and retain proof that reuse is blocked (config snapshots plus test results), and control exceptions with approvals and compensating controls. ²

Who it applies to (entity and operational context)

Applies to organizations pursuing CMMC Level 2 that handle CUI for the DoD in any system boundary covered by the assessment. ^{3 2}

Operationally, it applies to:

• Workforce identities (employees, contractors) that can authenticate into CUI-scoped systems.
• Privileged accounts (admins) used to manage CUI systems.
• Third-party identities (MSPs, consultants) if they authenticate into your CUI environment.
• Service and shared accounts if they are permitted (many orgs prohibit them; if you allow them, you still need a controlled password lifecycle). ¹

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

Step 1: Define scope and the “specified number of generations”

Create a short scoping statement that answers:

• Which identity stores are authoritative for CUI access?
• Which systems perform authentication (including federated authentication)?
• Which account populations are in scope?

Then define your “password history” requirement in a standard (or in your access control policy standard) as a single clear line item, for example: “Password history is enforced to prevent reuse of the last N passwords for all in-scope accounts.” Choose N based on your risk posture and system capabilities; the requirement is that it is specified and enforced. ¹

Step 2: Implement technical enforcement everywhere authentication happens

Build an “auth enforcement matrix” and configure each system accordingly:

Auth component	Typical enforcement method	What to capture as evidence
Directory service (e.g., AD/LDAP)	Password history / reuse prevention setting	Export or screenshots of policy and resulting effective settings
Cloud IdP / SSO	Password policy history setting; ensure it applies to the correct user groups	Policy configuration export; group scoping
VPN / remote access	If it delegates auth to IdP, ensure no bypass accounts exist; if local, set history there too	Auth method proof; local policy settings if used
Privileged Access Management	Password rotation and history controls (where PAM sets passwords)	Rotation policy configuration and logs
Endpoints (local accounts)	Local policy or management baseline if local accounts are enabled	Baseline configuration and compliance report

You are not required to use a specific product, but you are required to show consistent control operation across the boundary of the CUI environment. ²

Step 3: Address hard cases up front (exceptions, service accounts, federation)

Document decisions and implement controls for these common edge cases:

Federated identity / SSO: If an app relies on SSO, enforce password history at the IdP. Confirm there are no “local app accounts” with separate passwords that bypass the IdP policy. ²

Service accounts: If they cannot change passwords interactively, define a controlled rotation mechanism (often via PAM) and ensure the mechanism prevents reuse. If your tooling can’t guarantee history, restrict service account authentication paths and document a compensating control that reduces reuse risk. Keep the exception explicit and time-bound. ¹

Privileged break-glass accounts: Enforce history where possible. If an emergency account must be treated differently, document the rationale, storage controls, and post-use reset process. Assessors will look for discipline here because these accounts often bypass normal guardrails. ²

Step 4: Test the control and keep repeatable proof

Run a simple validation test per identity system:

• Change a test user password.
• Attempt to change it back to the previous password (and to another recent password, if feasible).
• Capture the system error showing reuse is blocked.

Repeat after any material identity policy change. Also, align your evidence collection to assessor expectations: show implementation + operation, not a one-time screenshot. ²

Step 5: Write the control narrative and map evidence

In your System Security Plan (SSP) or equivalent CMMC control narrative, state:

• the specified password history value (generations),
• where it is enforced (systems),
• which accounts are in scope,
• how exceptions are controlled,
• how you verify and retain evidence. ^{1 2}

Daydream (and similar GRC workflows) becomes useful here as the system of record for mapping the requirement to the control narrative, assigning evidence owners, and scheduling recurring evidence capture so you do not rebuild the package right before assessment. ²

Required evidence and artifacts to retain

Keep an assessor-ready evidence set that ties directly to enforcement:

1. Password standard/policy excerpt stating the password history (“generations”) requirement and in-scope populations. ¹
2. Configuration evidence per auth system (exports, screenshots, or policy objects) showing password history enforcement and scope (groups/OUs/tenants). ²
3. Test results demonstrating that reuse is blocked (ticket, change record, or test log plus screenshots). ²
4. Exception register for any accounts/systems that cannot meet password history, with approvals, rationale, compensating controls, and review cadence. ²
5. Account inventory for privileged and service accounts with ownership and authentication source to prove you did not miss populations. ²

Common exam/audit questions and hangups

Assessors and internal auditors tend to probe these points:

• “What is your specified number of generations, and where is it documented?” ¹
• “Show me the effective configuration in the system that authenticates CUI access.” ²
• “Does this apply to admins, service accounts, and third-party support identities?” ²
• “If you use SSO, where is password history enforced, and can any account bypass SSO?” ²
• “How do you prove this has been operating over time rather than set once?” ²

Frequent implementation mistakes and how to avoid them

1. Policy-only compliance. Fix: require technical enforcement evidence from each auth authority, not a PDF policy. ²
2. One directory configured, another missed. Fix: maintain an authentication architecture diagram and an “auth enforcement matrix” reviewed during changes. ²
3. Scope gaps for privileged accounts. Fix: place privileged accounts in groups with explicit password policy inheritance, then test those accounts. ²
4. Service accounts ignored. Fix: either prohibit them for interactive login, or manage them with controlled rotation and explicit exceptions where needed. ¹
5. No durable evidence trail. Fix: implement recurring evidence capture (config exports + tests) with accountable owners tracked in a GRC workflow. ²

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this specific practice, so this page focuses on assessment risk and operational exposure rather than penalty speculation. ²

From an assessment standpoint, the common failure mode is “inconsistent enforcement across the boundary.” That drives findings because the requirement is explicit: password reuse must be prohibited for a specified number of generations, and assessors can validate it quickly by checking effective policy and running a basic test. ¹

Operationally, password reuse increases the chance that a previously exposed password (from phishing, malware, or third-party compromise) becomes valid again. Preventing reuse reduces that reactivation path, especially for accounts that access CUI systems remotely. ¹

Practical 30/60/90-day execution plan

Next 30 days (stabilize and scope)

• Define the password history value (“generations”) and publish it in your authentication standard for CUI scope. ¹
• Build the inventory: identity providers, directories, VPN/auth gateways, PAM, and any apps with local authentication. ²
• Identify exception candidates (service accounts, break-glass, legacy systems) and open a tracked remediation plan for each. ²

Days 31–60 (implement and verify)

• Configure password history enforcement in each in-scope authentication system and verify group/OU scoping. ²
• Run and document validation tests for a normal user and an admin user in each auth authority. ²
• Draft the SSP/control narrative language and attach initial evidence artifacts in your GRC system of record (Daydream or equivalent). ²

Days 61–90 (operationalize and harden)

• Close or formally approve exceptions with compensating controls and an explicit review process. ²
• Add recurring evidence capture tasks to your control calendar: configuration snapshots after changes, plus periodic control testing. ²
• Run an internal “mini-assessment”: have someone outside IAM try to trace enforcement from policy to config to test proof for each auth path. ²

Frequently Asked Questions

What does “specified number of generations” mean in practice?

It means you choose and document a password history value and configure systems to block reuse of passwords within that remembered history. The assessor will look for both the stated value and the technical enforcement. ¹

Does this apply if we use MFA everywhere?

Yes. MFA reduces account takeover risk, but Practice 3.5.8 still requires password reuse prevention where passwords exist for authentication. Enforce it at the identity provider or directory that validates the password. ¹

If we use SSO, do we still need password history settings in each application?

If the application has no local passwords and relies fully on SSO, enforce password history at the IdP. If any app maintains local credentials as a fallback, that local store is in scope and needs enforcement or a controlled exception. ²

How should we handle service accounts that cannot change passwords normally?

Prefer non-interactive authentication methods and manage secrets through controlled rotation tooling where possible. If reuse prevention cannot be technically enforced, document an exception with compensating controls and tight access restrictions. ¹

What evidence is most persuasive to an assessor?

Effective configuration proof from the actual authenticating system plus a simple test showing the system blocks reuse. Pair that with an exception register so gaps are visible and governed. ²

Can we meet this requirement with a policy statement and user training?

No. Training and policy help, but “prohibit” implies technical enforcement. Keep the policy, then prove the systems enforce password history. ¹

Footnotes

1. NIST SP 800-171 Rev. 2

2. DoD CMMC Program Guidance

3. 32 CFR Part 170