CMMC Level 2 Practice 3.1.5: Employ the principle of least privilege, including for specific security functions and privileged

CMMC Level 2 Practice 3.1.5 requires you to enforce least privilege across your CUI environment so every user, process, and administrator has only the access needed to perform authorized tasks, including sensitive security administration functions. Operationalize it by defining privileged roles, reducing standing admin rights, implementing role-based access, and proving access is reviewed, approved, and logged. ¹

Key takeaways:

• Scope least privilege to the full CUI system boundary, including cloud consoles, endpoints, network gear, and security tools. ¹
• Treat “security functions and privileged” as a high-scrutiny category: stronger approvals, tighter role design, and better logging. ¹
• Evidence wins assessments: access matrices, role definitions, approval trails, periodic reviews, and privileged activity logs. ²

You can “have MFA” and “have accounts” and still fail this practice if administrators, service accounts, and security tool operators have broad rights by default. CMMC Level 2 Practice 3.1.5 focuses on least privilege with explicit attention to privileged access and security administration functions, because those permissions are the fastest path to full environment compromise and CUI exposure. This practice is mapped to NIST SP 800-171 Rev. 2 control 3.1.5, so assessors will expect you to implement it as a repeatable access governance process, not a one-time cleanup. ¹

For a Compliance Officer, CCO, or GRC lead, the fastest way to operationalize 3.1.5 is to translate “least privilege” into artifacts an assessor can test: a role catalog, an access control matrix, joiner/mover/leaver workflows, privileged access rules, and review evidence that shows your design operates in production. Align the implementation to your defined CUI system boundary under the CMMC Program so you can defend scope and avoid “shadow privilege” in adjacent IT systems that touch CUI. ^{3 2}

Regulatory text

Regulatory excerpt (as provided): “CMMC Level 2 practice mapped to NIST SP 800-171 Rev. 2 requirement 3.1.5 (Employ the principle of least privilege, including for specific security functions and privileged).” ^{1 2}

What the operator must do:
You must design and operate access controls so that users (including admins), system processes, and service accounts only have permissions required for approved tasks, and you must apply extra rigor to privileged permissions and security administration functions (for example: identity administration, endpoint security consoles, logging/SIEM administration, firewall rule changes). Demonstrate this through role design, approval controls, and ongoing review evidence within the CUI system boundary. ^{1 3}

Plain-English interpretation

Least privilege means “default deny, grant narrowly.” In practice, assessors look for:

• No broad, undefined roles like “IT Admin” that can do everything across the CUI environment.
• No standing admin by convenience (for example, engineers permanently in Domain Admins because it was easier).
• Tight scoping of security functions so the person who can change audit logs, disable EDR, or modify conditional access policies is explicitly authorized and monitored. ¹

A workable internal test: pick any privileged role and ask, “What tasks is this role allowed to do, in which systems, approved by whom, and where is it logged?” If you cannot answer crisply with artifacts, you have operational gaps.

Who it applies to (entity and operational context)

Entities: Defense contractors and federal contractors that handle CUI and must achieve CMMC Level 2. ³
Operational context: Any system in your CUI system boundary where identity and access is enforced or where access can impact confidentiality of CUI, including:

• Identity providers and directories (for example, AD/Azure AD/Entra ID)
• Cloud platforms and SaaS hosting CUI (for example, M365 tenants used for CUI)
• Endpoints and servers that store/process/transmit CUI
• Network devices controlling CUI traffic
• Security tooling that can alter protective controls or logs (EDR, SIEM, vulnerability scanners) ^{2 1}

Also in scope: third parties with administrative access into your CUI environment (MSPs, IR retainers, cloud admins). They are “users” for least privilege purposes.

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

1) Define the CUI system boundary and “privileged” categories

• List in-scope systems where access grants matter (IdP, endpoints, file shares, code repos, ticketing admin, security consoles).
• Define privileged access types:
  • Identity/Directory administration
  • System administration (servers/endpoints)
  • Network administration (firewalls/VPN)
  • Security tooling administration (EDR/SIEM/log management)
  • Cloud platform administration (subscriptions/projects, key vaults)
  • “Break-glass” emergency access ²

Deliverable: a boundary list and a privileged-access taxonomy you can use consistently.

2) Build a role catalog and access control matrix (RBAC is the default pattern)

Create:

• Role catalog: role name, purpose, systems covered, allowed actions, constraints.
• Access control matrix: job functions mapped to roles; roles mapped to systems/permissions.

Practical rules that pass tests:

• Separate read-only from admin roles in security tools.
• Separate policy change from policy view in identity/security platforms.
• Split duties so the same person cannot both approve and implement privileged changes without an independent check, when feasible.

3) Remove standing admin rights and implement controlled elevation

Minimum operational baseline:

• Standard user accounts for daily work.
• Separate admin accounts for privileged tasks, scoped to specific systems.
• A documented method for elevation (PAM tool, privileged role assignment workflow, or tightly controlled group membership changes with approval and logging).

If you cannot deploy PAM quickly, you can still meet intent by using:

• Time-bounded group membership with ticket-based approvals
• Dedicated admin workstations for privileged tasks
• Strong conditional access rules for admin accounts (your assessor will still expect least privilege plus demonstrable control) ¹

4) Implement a joiner/mover/leaver (JML) workflow with approvals

Operational steps:

• Joiner: manager request → role selection from catalog → data owner approval for CUI repositories → provisioning.
• Mover: access recertification when job changes; remove old roles first, then grant new.
• Leaver: immediate disablement; remove sessions/tokens if supported; reclaim admin accounts/keys.

Make approvals auditable (ticketing system or IAM request logs). “Verbal approval” fails under scrutiny.

5) Control service accounts and non-human privileges

Assessors routinely find gaps here.

• Inventory service accounts used in the CUI boundary.
• Assign each service account an owner, purpose, and allowed systems.
• Grant only the specific API permissions needed.
• Prohibit interactive login unless justified and approved.
• Rotate secrets/keys using an enterprise secret store where possible, and document rotation rules.

6) Monitor and review privileged access

Set a review cadence you can sustain and defend:

• Periodic review of privileged group membership and admin role assignments.
• Review of privileged actions in key systems (identity provider, cloud control plane, security tools).
• Track findings to closure with tickets and evidence of removal.

This is where many programs fail: they design RBAC but do not prove it runs.

7) Create a “control card” and evidence bundle (operationalization)

Turn 3.1.5 into a runbook:

• Objective: least privilege enforced for all users, privileged roles, and security functions.
• Owner: IAM owner + security owner; GRC monitors.
• Trigger events: onboarding, role changes, tool onboarding, incident response, M&A.
• Exception rules: documented, time-bound, risk-accepted, reviewed.
• Evidence bundle: see next section. ³

Daydream can help by turning the role catalog, review cadence, and evidence bundle into an assignable control workflow so you can prove ongoing operation without building a spreadsheet-only program.

Required evidence and artifacts to retain

Keep evidence tied to the CUI boundary and make it easy to sample.

Core artifacts

• Access control policy/standard addressing least privilege and privileged access. ¹
• CUI boundary definition and in-scope system inventory. ³
• Role catalog and access control matrix (job function → role → permissions).
• Privileged account inventory (human admins and third-party admin accounts).
• Service account inventory with owners, purpose, and permissions.

Operational evidence (assessor-ready)

• Samples of access requests with approvals (tickets/workflow records).
• Provisioning/deprovisioning logs for joiner/mover/leaver events.
• Group membership exports for privileged groups (before/after changes).
• Privileged access reviews: reviewer, date, population reviewed, findings, remediation tickets, closure evidence.
• Logs from identity/cloud/security tools showing privileged actions (or at least that logging is enabled and retained per your logging approach). ²

Common exam/audit questions and hangups

• “Show me your privileged roles. Who is in them today, and why?”
• “How do you ensure security tool admins are limited and monitored?” ¹
• “How do you control service accounts and API keys?”
• “When someone changes roles, how do you remove the old access?”
• “Prove least privilege is enforced in the cloud console, not just on-prem.”
  Hangup pattern: teams show a policy and a screenshot of an admin group, but no role definitions, no approvals, and no recurring reviews.

Frequent implementation mistakes and how to avoid them

1. One giant admin group
   Fix: create system-specific admin roles; require ticketed approvals for membership.

2. EDR/SIEM admins = domain admins
   Fix: separate tool administration from OS/domain administration; grant the minimum console rights.

3. Service accounts with interactive login and broad permissions
   Fix: lock to non-interactive where possible; scope permissions to a single app/workload; assign an accountable owner.

4. No evidence of periodic review
   Fix: schedule recertification, export membership lists, capture reviewer sign-off, open remediation tickets, and retain closure evidence. Daydream-style control health checks work well here because they force artifacts into a predictable repository.

5. Third-party admin access not governed
   Fix: treat third-party identities like internal privileged users: named accounts, scoped roles, documented approvals, and monitored activity.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement. CMMC is implemented through contractual and assessment mechanisms under the CMMC Program, so your practical risk is assessment failure, delayed awards, or loss of eligibility for work requiring CMMC Level 2 certification. ^{3 2}

Operational risk is straightforward: excessive privileges expand blast radius. Privileged and security-function permissions can disable controls, erase logs, and exfiltrate CUI. Least privilege reduces the likelihood that a single compromised account becomes a full environment event. ¹

A practical 30/60/90-day execution plan

First 30 days (stabilize and scope)

• Confirm the CUI system boundary and list in-scope platforms for access governance. ³
• Identify all privileged groups/roles across those platforms; export current membership.
• Freeze creation of new “catch-all admin” roles; require approvals for any new privileged access.
• Inventory service accounts in the boundary; assign owners.

Next 60 days (implement enforceable least privilege)

• Publish the role catalog and access control matrix for core job functions.
• Remove standing admin from daily accounts; create separate admin accounts where needed.
• Implement a consistent approval workflow (ticket + approver + retention location).
• Configure logging for privileged actions in identity/cloud/security tools per your logging approach. ²

Next 90 days (prove operation and close evidence gaps)

• Run the first formal privileged access recertification; document results and remediation.
• Validate service accounts have scoped permissions; remediate broad rights.
• Perform a control health check: sample access grants end-to-end (request → approval → provisioning → logging → review).
• Package the evidence bundle for assessment: role matrix, approval samples, review outputs, and change/removal proofs. ¹

Frequently Asked Questions

Does least privilege require a dedicated PAM tool?

No. A PAM tool can make enforcement and evidence easier, but you can meet the requirement with tightly scoped roles, ticketed approvals, separate admin accounts, and logged, reviewable privileged actions. ¹

How do I define “specific security functions” for 3.1.5?

Treat administration of identity, logging, endpoint security, vulnerability tooling, and network security controls as security functions. Document which tools are in scope and create explicit roles for “view,” “operator,” and “admin” actions where the platform supports it. ¹

Are service accounts in scope for least privilege?

Yes. Service accounts often carry broad rights and are frequently missed in reviews. Keep an inventory with owners and purposes, restrict permissions to only what the service needs, and control credentials. ¹

What evidence is most likely to be sampled by a CMMC assessor?

Expect sampling of privileged role memberships, access request approvals, service account permissions, and proof of periodic reviews with remediation closure. Keep exports and tickets tied to the CUI boundary systems. ²

How do I handle emergency “break-glass” access without failing least privilege?

Create a dedicated emergency account with strong protections, documented conditions for use, and post-use review. Record the incident/ticket, who approved, what actions were taken, and when access was reset. ¹

Do third-party administrators (MSPs) need the same least privilege controls?

Yes. If a third party can administer in-scope systems, control their access through named accounts, scoped roles, approval trails, and monitoring. Treat them as privileged users for evidence and review. ¹

Footnotes

1. NIST SP 800-171 Rev. 2

2. DoD CMMC Program Guidance

3. 32 CFR Part 170