SC-3(3): Minimize Nonsecurity Functionality

To meet the sc-3(3): minimize nonsecurity functionality requirement, you must keep the isolation boundary that contains security functions as “clean” as possible by excluding unrelated application and management features. In practice, this means defining the boundary, inventorying what runs inside it, removing nonessential services, and proving ongoing configuration control and change governance. ¹

Key takeaways:

• Treat the “isolation boundary” as a high-assurance zone: security functions go in; everything else stays out or gets tightly justified.
• Your core work is architectural and operational: boundary definition, component inventory, hardening, and change control.
• Auditors will ask for evidence that nonsecurity functionality was identified, removed/disabled, and prevented from creeping back in.

SC-3(3) is a design-and-operations requirement aimed at keeping your security enforcement and security management components from becoming bloated, fragile, or overexposed. The control language is short, but the operational implication is not: you need an explicit isolation boundary for security functions, and you need discipline to keep nonsecurity functionality from accumulating inside that boundary over time. ¹

If you run federal information systems or you are a contractor handling federal data, this shows up in assessments because it is assessable through architecture diagrams, build standards, and configuration evidence. ¹ It also maps cleanly to common failure modes: “security appliances” running extra admin tools, bastions that turn into general-purpose jump boxes, and identity/security management servers with unrelated packages installed “for convenience.”

This page gives requirement-level implementation guidance you can execute quickly: how to define the isolation boundary, what to remove or relocate, how to set guardrails in CI/CD and infrastructure-as-code, and what evidence to retain for a defensible assessment narrative. Where tooling can reduce audit friction, Daydream can help you map ownership, procedure, and recurring evidence so SC-3(3) stays operational rather than a one-time cleanup.

Regulatory text

Requirement (verbatim): “Minimize the number of nonsecurity functions included within the isolation boundary containing security functions.” ¹

Operator translation:

1. Identify the isolation boundary that contains your security functions (examples: IAM service boundary, key management boundary, logging/SIEM ingestion boundary, security orchestration boundary).
2. Identify what is “nonsecurity functionality” inside that boundary (anything not required to provide, administer, or protect the security function).
3. Remove, disable, or relocate nonsecurity functionality, and prevent it from returning through change control and build standards. ¹

Plain-English interpretation (what “counts”)

What is an “isolation boundary” here?

A defensible isolation boundary is a clearly defined set of components (hosts, containers, managed services, network segments, accounts/subscriptions/projects, and admin planes) that collectively provide security functions and are treated as higher-trust/higher-assurance than the rest of the environment.

You should be able to point to:

• Where the boundary starts/ends (networks, accounts, clusters, tenants).
• Which components are inside it (by asset ID, tag, or CMDB record).
• What security functions it provides (authN/authZ, crypto/key custody, security monitoring, policy enforcement). ¹

What is “nonsecurity functionality”?

Nonsecurity functionality is “business” or general-purpose functionality that is not necessary to deliver the security function. Common examples you will see in the field:

• A bastion host that also runs file transfer tools, database clients for routine ops, or user productivity tooling.
• An identity server that also runs unrelated web apps, build agents, or local dev/test utilities.
• A security logging pipeline that also hosts unrelated ETL jobs because it already has access to many data sources.

The control does not require “zero” extra functions. It requires minimization. Your job is to reduce attack surface and complexity inside the boundary and to show you made deliberate, documented choices. ¹

Who it applies to (entity + operational context)

In scope entities

• Federal information systems. ¹
• Contractor systems handling federal data. ¹

In scope operational contexts

• Any environment where security functions are implemented with dedicated components or services (cloud security accounts, on-prem security enclaves, segmented admin networks).
• Any “security plane” that, if compromised, would allow an attacker to disable controls, mint credentials, alter logs, or change policy enforcement.

If you are a CCO/GRC lead, treat this as an architecture control with DevOps/infra ownership, plus governance owned by security engineering with GRC oversight.

What you actually need to do (step-by-step)

Step 1: Name the security functions and the boundary

Create a short SC-3(3) scope statement:

• Security functions provided (list).
• Boundary definition (network segment/account/cluster/tenant).
• Control owner and technical custodians.

Deliverable: “SC-3(3) boundary statement” mapped to your system security plan or control register. ¹

Step 2: Inventory everything inside the boundary

Produce an inventory that is specific enough to audit:

• Compute: instances, images, containers, functions.
• Managed services: KMS/HSM, IAM directory, SIEM, secrets manager, policy engines.
• Packages and services on hosts (where applicable).
• Admin access paths (bastions, VPNs, management endpoints).

Practical tip: tag boundary assets (for example security_boundary=true) so you can query cloud inventory and drive alerts when a new asset appears inside the boundary.

Step 3: Classify each component/function as “security” vs “nonsecurity”

Create a decision table and apply it consistently:

Question	If “yes”	If “no”
Is it required to deliver the security function (enforcement, monitoring, key custody, identity)?	Keep (document purpose)	Candidate for removal
Is it required to administer the security function securely (patching agent, EDR, config mgmt, logging)?	Keep (document)	Candidate for removal
Does it expand inbound exposure or add interactive tooling?	Strong removal bias	Investigate compensating controls
Can it be moved outside boundary without breaking assurance?	Move	Justify why not

Deliverable: Component classification worksheet with owner sign-off.

Step 4: Remove/disable/relocate nonsecurity functionality

Common actions that satisfy minimization:

• Remove extra packages, agents, and local tooling from security hosts.
• Split “combo” servers into separate roles (security plane vs app plane).
• Move ad hoc scripts and jobs into a separate automation account/runner outside the boundary.
• Lock down inbound connectivity and exposed ports to only what the security function needs.

You do not need to boil the ocean. Prioritize removals that reduce:

• Internet exposure,
• interactive admin surfaces,
• lateral movement paths into identity, key custody, and logging. ¹

Step 5: Put guardrails in place to prevent drift

Minimization fails over time without guardrails. Implement:

• Hardened golden images for boundary hosts with a tight allowlist of packages.
• Infrastructure-as-code policy checks that block non-approved resources inside boundary accounts/subnets.
• Change control hooks: boundary changes require security engineering approval and a ticket that includes a “nonsecurity functionality impact” line item.
• Continuous configuration monitoring: alerts when new listening services/packages appear.

Deliverable: Boundary build standard + approval workflow.

Step 6: Make it auditable (control narrative + recurring evidence)

Write a short control narrative:

• How the boundary is defined.
• How inventory is maintained.
• How nonsecurity functionality is identified and minimized.
• How changes are reviewed and evidenced. ¹

Daydream fit: use Daydream to map SC-3(3) to a control owner, a concrete implementation procedure, and a recurring evidence list so collection is routine and not a scramble at assessment time. ¹

Required evidence and artifacts to retain

Keep artifacts that prove both design and operation:

1. Boundary definition

• Network/account/tenant diagram with labeled boundary
• Asset tagging standard or boundary membership criteria

2. Component inventory

• Export from CMDB/cloud inventory filtered to boundary tag
• Host/service lists for key boundary systems

3. Minimization analysis

• Classification worksheet (security vs nonsecurity) with rationale
• Risk acceptance records for any nonsecurity items you kept

4. Configuration evidence

• Baseline configs (CIS-style hardening notes are fine if internally defined)
• Golden image build manifest or SBOM-like package list for boundary images
• Screenshots/exports of security group/firewall rules showing minimal exposure

5. Change governance

• Change tickets showing review and approval for boundary modifications
• CI/CD or IaC policy logs that show preventative controls

6. Ongoing monitoring

• Alerts or reports that detect drift (new services, new assets in boundary)
• Remediation tickets showing response when drift occurred

Common exam/audit questions and hangups

Expect assessors to push on these points:

• “Show me the boundary.” If your diagram is vague, you will lose time. Provide explicit identifiers (account IDs, VPC/subnet names, cluster names).
• “What is inside it today?” Have an inventory export ready, not a narrative.
• “How did you decide what is nonsecurity?” Bring your decision table and examples.
• “How do you stop re-introducing tools?” Point to build standards, allowlists, and change gates.
• “Where is the evidence?” If you cannot produce artifacts quickly, the control reads as aspirational rather than operating. ¹

Frequent implementation mistakes (and how to avoid them)

1. Treating bastions as general-purpose admin workstations
   Fix: limit bastions to remote access tooling required for privileged access; move everything else to managed endpoints outside the security boundary.

2. No explicit boundary membership rule
   Fix: document objective criteria (tags, accounts, subnets) and make inventory queries reproducible.

3. Keeping “temporary” troubleshooting tools permanently
   Fix: allow break-glass procedures with time-bound exceptions and mandatory removal verification.

4. Minimization done once, then forgotten
   Fix: add drift detection and require boundary review in change management for any component added to the boundary.

5. Over-scoping the boundary
   Fix: keep the boundary tight. If everything is “security boundary,” minimization becomes impossible to demonstrate.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement, so this page does not cite enforcement actions.

Operational risk is still clear: extra nonsecurity functionality inside a security isolation boundary raises attack surface, increases patch burden, and creates more paths for privilege escalation into the systems that enforce your controls. The control’s intent is reduction of those paths through minimization. ¹

Practical 30/60/90-day execution plan

First 30 days: Define and see the boundary

• Assign control owner and technical owner(s).
• Publish the boundary statement and draft diagram.
• Tag boundary assets and produce an initial inventory export.
• Identify the highest-risk nonsecurity functionality candidates (interactive tools, exposed services, “combo” servers).

Days 31–60: Remove the obvious, document the rest

• Execute removals/relocations with change tickets.
• Create the classification worksheet with rationale and sign-off.
• Implement golden image/baseline package allowlists for boundary systems.
• Add an approval gate for new assets or software inside the boundary.

Days 61–90: Make it repeatable and audit-ready

• Turn the inventory export and drift checks into recurring evidence.
• Integrate IaC policy checks to block boundary expansion without approval.
• Run an internal assessment: pick a boundary component and prove, end-to-end, that nonsecurity functionality is minimized and controlled.
• In Daydream, map SC-3(3) to owners, procedures, and evidence so audits pull from a stable record. ¹

Frequently Asked Questions

What counts as a “security function” for SC-3(3)?

Treat security functions as capabilities that enforce, monitor, or administer security controls, such as identity, key management, security logging, and policy enforcement. Document your list and keep it stable so boundary decisions stay consistent. ¹

Do I have to eliminate all nonsecurity functionality inside the boundary?

The requirement is minimization, not absolute elimination. Keep a short, specific justification for any nonsecurity item you retain and show compensating controls and approval. ¹

How do we prove “minimize” to an auditor without a numeric threshold?

Prove the decision process and the outcomes: an inventory, a classification table, removal tickets, and preventative guardrails. Auditors look for disciplined scope control and evidence that drift is detected and corrected.

Does this apply to managed cloud services like hosted IAM or KMS?

Yes, the boundary can include managed services. Your minimization work shifts toward tenant configuration, access paths, integrations, and keeping unrelated workloads out of the same administrative boundary. ¹

Our security tooling stack needs plugins and agents. Is that “nonsecurity functionality”?

If the plugin/agent is required to provide or securely operate the security function, it fits the security purpose. Treat optional plugins as nonsecurity until you document why they are necessary and control their configuration.

What’s the fastest way to operationalize SC-3(3) across multiple systems?

Standardize a boundary definition template, a package/service allowlist baseline, and an evidence checklist. Use a system like Daydream to keep owner mappings and recurring evidence consistent across programs. ¹

Footnotes

1. NIST SP 800-53 Rev. 5 OSCAL JSON