03.01.05 – Least Privilege (NIST 800-171 Rev. 3)

2025-06-02

Welcome to our breakdown of 03.01.05 – Least Privilege, part of the Access Control family in NIST SP 800-171 Revision 3.

This control is one of the most important cybersecurity fundamentals — and now, it comes with tightened guidance from the DoD. The principle is simple: Give users and systems only the access they truly need.

03.01.05 – Least Privilege

The Least Privilege control ensures that users, scripts, and services can only perform actions necessary to accomplish their assigned tasks. It’s about reducing your attack surface and limiting the potential fallout of compromised credentials or insider threats.

• Reduce unnecessary access to sensitive systems or data
• Prevent privilege escalation from low-level accounts
• Enforce discipline across accounts — human and non-human

A script used for automated backups should not have admin-level access to modify firewall settings.

03.01.05 – Key Requirements

To comply with this control, organizations must:

• Allow only authorized access for users or processes, based on their job function
• Authorize access to specific security functions and security-relevant information
• Review privileges assigned to roles or classes of users at a defined frequency
• Reassign or remove privileges when no longer needed

🛑 This is not a set-it-and-forget-it control. Least Privilege must be implemented, enforced, and reviewed — regularly.

🚨 DoD-Defined Parameters (Rev. 3)

In NIST SP 800-171 Rev. 3, the Department of Defense has specified minimum values for certain parameters that were previously left up to each organization.

• Security functions that must be protected include:

  • System account creation and privilege assignment
  • Configuration of access authorizations
  • Audit settings and management of audit information
  • Vulnerability scan parameters
  • Intrusion detection settings

• Security-relevant information requiring restricted access includes:

  • Threat and vulnerability data
  • Firewall or router filtering rules
  • Security service configurations and key management info
  • Security architecture and access control lists (ACLs)
  • Audit logs and related records

• Access privilege reviews must occur at least every 12 months

These are no longer suggestions — they are required minimums.

03.01.05 – Implementation Tips

Here’s how to implement this control effectively:

• Identify your security functions and security-relevant data
• Define which roles require access — and why
• Use RBAC (role-based access control) to enforce separation
• Review all access authorizations at least annually
• Restrict service accounts, scripts, and admin tools appropriately
• Document procedures for assigning, updating, and revoking privileges

03.01.05 – Evidence

To demonstrate compliance, be ready to provide:

• Access control policies and written procedures
• Role definitions and assigned access permissions
• Logs or tickets documenting privilege reviews and changes
• System settings showing access limitations
• SSP documentation showing how least privilege is implemented

Include in your SSP

You should document:

• What constitutes a privileged function or information in your environment
• How access is granted, reviewed, and revoked
• Your review schedule (e.g. annually) and responsible personnel

Why it matters..

Least Privilege isn’t just a checkbox — it’s a philosophy.
When access is kept minimal and intentional, systems become more resilient against compromise and human error.

Limiting permissions is one of the most effective ways to contain a breach.

• Role-based dashboards and access mapping
• Auto-flagging of privilege creep and unused permissions
• Audit-ready access logs tied to SSP controls
• Built-in reminders for annual access reviews

Next up in this NIST 800-171 Rev. 3 series: 03.01.06 – Least Privilege: Privileged Accounts
We’ll cover how elevated accounts like admins and system operators should be secured and restricted.