03.01.10 – Device Lock (NIST 800-171 Rev. 3)

2025-06-15

Welcome back to our series on NIST SP 800-171 Revision 3. Today we’re walking through Control 03.01.10 – Device Lock, part of the Access Control family.

This control protects systems from unauthorized access when a user steps away — even for a moment — by requiring automatic device locks and screen concealment after inactivity.

03.01.10 – Device Lock

If someone walks away from an unlocked screen, it’s an open door for misuse. Device locks are designed to close that door by automatically triggering after a period of inactivity — and requiring users to log back in to resume.

Just remember: locking a device is for short absences. It does not replace logging out at the end of a session.

03.01.10 – Key Requirements

To comply with this control, organizations must:

• Automatically initiate a lock after a period of inactivity
• Encourage or require users to manually lock devices when stepping away
• Ensure the lock remains until the user reauthenticates
• Hide sensitive information while the device is locked (e.g., blank screen or clock)

🚨 DoD-Defined Parameters (Rev. 3)

• SR-03.01.10.a: Automatically initiate a device lock after no more than 15 minutes of inactivity.

• Require users to manually lock the device before leaving it unattended.

• SR-03.01.10.b: The lock must remain active until reauthentication using login credentials.

• SR-03.01.10.c: The lock screen must conceal sensitive data (e.g., no visible applications or files).

These are mandatory enforcement points — not recommendations.

03.01.10 – Implementation Tips

To implement this effectively:

• Use OS-level settings to enforce auto-lock after 15 minutes (or less)
• Standardize lock behavior using group policies or MDM tools
• Educate users to manually lock their device — using Win+L or Control+Command+Q
• Ensure lock screens hide open windows or files
• Document all device lock settings and practices in your System Security Plan (SSP)

🛡️ A device left open is a device left vulnerable.

03.01.10 – Evidence

When it’s audit time, you should be ready to show:

• Screenshots showing inactivity timeout and lock screen settings
• Policy documentation requiring lock after 15 minutes of inactivity
• Language requiring users to lock their screens manually when stepping away
• Proof that lockout remains until login credentials are entered
• Screenshots or samples of approved screensavers or blank screen configurations
• Interview responses from admins or endpoint managers confirming these settings

Why it matters..

A user stepping away for just a few minutes can unintentionally expose sensitive data. Device locks add a critical safety net — combining automation with user accountability to reduce risk and meet compliance expectations.

Every unlocked screen is an opportunity. Device locks close that window — fast.

• Set and verify lockout thresholds across fleets
• Sync settings with MDM and Active Directory
• Track user lock compliance in real time
• Export reports for SSP inclusion and audit review

Next up in our NIST 800-171 Rev. 3 series: 03.01.11 – Session Termination. We’ll explore how to properly end sessions — and why that’s more than just locking the screen.