NIST 800-53 REV 5 • CONTINGENCY PLANNING
CP-12 — Safe Mode
When {{ insert: param, cp-12_odp.02 }} are detected, enter a safe mode of operation with {{ insert: param, cp-12_odp.01 }}.
Supplemental Guidance
For systems that support critical mission and business functions—including military operations, civilian space operations, nuclear power plant operations, and air traffic control operations (especially real-time operational environments)—organizations can identify certain conditions under which those systems revert to a predefined safe mode of operation. The safe mode of operation, which can be activated either automatically or manually, restricts the operations that systems can execute when those conditions are encountered. Restriction includes allowing only selected functions to execute that can be carried out under limited power or with reduced communications bandwidth.
Practitioner Notes
Safe mode means your system can continue operating in a degraded but secure state when full functionality is not available — maintaining security even when not everything is working.
Example 1: Configure your firewall to fail closed (block all traffic) rather than fail open if it experiences a critical error, preventing unsecured traffic during the outage.
Example 2: Design your web application to display a maintenance page and reject all user sessions gracefully if the authentication backend becomes unavailable, rather than bypassing authentication.