Firewall fails open misconfig
Test shows certain ACL engine fails open. SC-24 redesign forces fail closed for ePHI segments.
Fail in Known State
High Risk
Complex
Medium Cost
SC-24 requires failing to a known-state for organization-defined system components under defined failure conditions, preserving system state information in failure, and restricting subsequent processing. Clinical systems that fail open to anonymous access or wipe forensic state create both safety and HIPAA problems.
Control Objective
Configure critical ePHI system components to fail into documented known states that prefer security and recoverability — preserving evidence and preventing unauthorized processing after failure.
Implementation Guidance
- Identify failure modes for critical components (auth services, firewalls, EHR app nodes, encryption services).
- Define desired known states (fail closed on admin APIs, maintain last-known ACLs, preserve logs).
- Avoid fail-open to unauthenticated ePHI access.
- Ensure crash dumps/logs do not unnecessarily expose ePHI; protect them.
- Test failure behavior in non-prod.
- Document manual safe state if automation limited (CP-12 alignment).
- Monitor for components that reboot into default insecure configs.
- Include network devices that might fail open.
Real-World Use Cases
How this control shows up in healthcare and HIPAA-covered environments.
Auth service outage
EHR configured to deny new sessions rather than allow anonymous chart access — known secure state.
Node crash preserves audit
Application servers write critical audit buffers before shutdown where supported.
Best Practices
- Document known failure states.
- Prefer fail closed for ePHI access paths.
- Preserve logs/forensics securely.
- Test failure modes.
- Watch default insecure reboot configs.
- Align with CP-12 safe mode.
Common Gaps & Violations
- Firewalls fail open on ePHI VLANs.
- Apps allow guest access when IdP down.
- Crash dumps with clear ePHI on open shares.
- Never testing failure behavior.
- Devices reload factory defaults.
Required Documentation
- Fail-in-known-state standard (SC-24)
- Per-component failure state definitions
- Test results from failure scenarios
- Log/crashdump protection procedures
- Alignment notes to CP-12
How to Test & Validate
- Review firewall/IdP failure behavior documentation.
- Test or review evidence of fail closed for an ePHI path.
- Inspect crashdump handling for ePHI exposure.
- Check network device failure modes.
- Confirm monitoring detects insecure default reloads.
Audit Considerations
Failure behavior is part of secure design. Assessors may ask what happens to access control when dependencies die — SC-24 answers with tested known states.
HIPAA Mapping
How this NIST control supports HIPAA Security Rule expectations.
- 164.312(a) Access Control — access control must not vanish into anonymous allow on failure.
- 164.312(b) Audit Controls — preserve audit capability/state through failures when feasible.
- 164.308(a)(7) Contingency Plan — known failure states support orderly contingency.
- 164.306 CIA — integrity and confidentiality during failure modes.
Compliance Tips
- Explicitly test IdP-down behavior for EHR.
- Ban fail-open on firewalls guarding ePHI.
- Protect crash dumps like production data.
Frequently Asked Questions
Does fail closed harm patient care?
Balance with clinical safety — define known states with clinical leaders (e.g., break-glass read-only) rather than anonymous full access.
How related to CP-12?
CP-12 is intentional safe mode; SC-24 is failure-induced known state — design them consistently.
Are SaaS failure modes our problem?
Understand provider behavior and configure your side (cached auth, break-glass) accordingly; document shared responsibility.
References & Resources
- NIST SP 800-53 Rev. 5 — SC-24
- Related controls: CP-12, CP-10, SI-7, AU-5, SC-5
Related Guidelines
Related controls that commonly accompany SC-24.
Need Help Implementing SC-24?
Our auditors map NIST SP 800-53 controls to your HIPAA Security Rule program — policies, technical evidence, and audit readiness.