Security requirement
- a.Design the security architecture for the system using a defense-in-depth approach.
- b.Allocate [Organization-defined: security requirements] to [Organization-defined: architectural layers and locations].
- c.Ensure that the allocated requirements operate in a coordinated and mutually reinforcing manner.
Discussion
Organizations strategically allocate security requirements and the associated protection mechanisms in the security architecture so that adversaries must overcome multiple defensive layers to achieve their objective. Requiring adversaries to defeat multiple defensive layers makes it more difficult to attack systems by increasing the work factor of the adversary. It also increases the likelihood of detection. Defense-in-depth architectural approaches include modularity and layering, the separation of system and user functionality, and security function isolation.
The coordination of allocated security requirements is essential to help ensure that an attack that involves one requirement does not create adverse, unintended consequences (e.g., system lockout and cascading alarms) by interfering with other requirements. The value of organizational assets and the impacts or consequences of loss are important considerations in providing additional defensive layers. This requirement does not enhance a specific requirement in SP 800-171 but can be used to strengthen the protection of CUI associated with critical programs or high value assets.
Tailoring decisions required
Resolve these values through the governing organization’s approved tailoring and risk-management process before declaring the requirement implemented.
Protection strategies supported
These classifications are carried from the official SP 800-172 OSCAL record and help explain the enhanced requirement’s defensive purpose.
Implementation perspective
Treat Defense In Depth as an enhanced CUI protection outcome for elevated threat conditions that must be reflected in the system boundary, documented implementation, operational behavior, and assessment evidence. Pay particular attention to accurate plans, architecture, rules of behavior, system boundaries, and lifecycle alignment for CUI protection.
- Confirm the federal agency selected this enhanced requirement for the critical program or high-value asset and identify the CUI system components, services, users, and external connections in scope.
- Resolve every organization-defined parameter through an approved governance and tailoring process.
- Map each clause of the requirement to an accountable owner, implementation mechanism, and evidence source.
- Verify that inherited and shared implementations are supported by current provider evidence and responsibility boundaries.
- Collect evidence during normal operation and review changes, exceptions, and deficiencies on a risk-based cadence.
Questions to ask
- Which critical-program or high-value-asset CUI, data flows, users, and services are protected by this enhanced requirement?
- Which portions are implemented locally, inherited, shared, or not applicable, and what evidence supports that determination?
- Do the system security plan, deployed configuration, operating process, and assessment evidence tell the same story?
- What change, incident, or threshold should trigger reassessment?
Evidence and validation
- system security plans
- architecture and data-flow diagrams
- rules-of-behavior acknowledgments
- plan review and approval records
Common failure patterns
- plans copied from templates without system specificity
- diagrams that do not match deployed services
- inherited protection claimed without provider evidence
- plans updated only before assessment
Assessment objectives and methods
Assessment objectives (3)
- a.
the security architecture for the system is designed using a defense-in-depth approach.
- b.
[Organization-defined: security requirements] are allocated to [Organization-defined: architectural layers and locations] .
- c.
the security requirements allocated to the architectural layers and locations are coordinated and mutually reinforcing.
Examine
- Security planning policy
- procedures addressing information security architecture development
- enterprise architecture documentation
- information security architecture documentation
- system security plan
- security CONOPS for the system
- other relevant documents or records
Interview
- Personnel with information security responsibilities
- personnel with information security architecture development responsibilities
- personnel with security planning and plan implementation responsibilities
Test
- Processes for designing the information security architecture
- mechanisms supporting and/or implementing the design of the information security architecture
Source NIST SP 800-53 controls
These controls are referenced by the official SP 800-172 Rev. 3 OSCAL record. Open the corresponding control pages for complete control text, enhancements, D3FEND mappings, and related learning.
Authoritative sources
- NIST SP 800-172 Revision 3 official publication ↗
- NIST SP 800-172A Revision 3 official publication ↗
- NIST OSCAL Content release used for this import ↗
Bare Metal Cyber is an independent educational publisher and is not affiliated with or endorsed by NIST. The official publications, the responsible federal agency, and the governing contract or agreement determine applicability, tailoring, assessment depth, and required implementation.