SI-4(23): Host-based Devices

To meet the si-4(23): host-based devices requirement, you must deploy and operate host-based monitoring mechanisms on the in-scope endpoints (the “where”) and implement the specific mechanism types your system defines (the “what”), then retain evidence that the tools are installed, configured, reporting, and acted on. This is about reliable endpoint visibility, not a policy statement. ¹

Key takeaways:

• Define scope first: which host types and environments require host-based monitoring, and which are explicitly excluded with rationale.
• Standardize the mechanism set per host class (e.g., EDR, file integrity monitoring, host firewall telemetry) and enforce configuration baselines.
• Prove operations: show deployment coverage, alert routing, triage workflows, and tuning or exception handling with durable artifacts.

SI-4(23) is an enhancement under NIST SP 800-53’s System Monitoring control family that pushes monitoring down to the endpoint. Network monitoring alone misses activity that happens “on-host” (local privilege escalation, malicious processes, registry changes, suspicious child processes, unsigned binaries, persistence mechanisms, and destructive commands executed without clear network indicators). SI-4(23) closes that gap by requiring you to implement host-based monitoring mechanisms at defined locations.

Operationally, the hard part is not buying an EDR tool. The hard part is making the requirement assessable: scoping the in-scope devices, choosing and documenting the required host-based mechanisms, deploying them consistently, routing alerts to a team that can act, and retaining evidence that the program runs continuously. Assessors typically look for gaps created by unmanaged endpoints, broken agents, inconsistent configurations, and “alert-only” deployments with no response workflow.

This page turns the requirement into an execution checklist a Compliance Officer, CCO, or GRC lead can hand to endpoint engineering and security operations, while still producing clean evidence for audits aligned to NIST SP 800-53 Rev. 5. ²

Regulatory text

NIST SI-4(23): Host-based Devices states:

“Implement the following host-based monitoring mechanisms at [organization-defined location(s)]: [organization-defined host-based monitoring mechanisms].” ¹

What the operator must do

This enhancement has two required decisions you must make and document:

1. Where host-based monitoring must run (the “organization-defined location(s)”).
   In practice, this means specifying which endpoint populations are in scope: workstations, servers, cloud instances, VDI, mobile endpoints, privileged admin workstations, OT/IoT hosts, or high-value assets.

2. What mechanisms you will implement (the “organization-defined host-based monitoring mechanisms”).
   This means naming the endpoint monitoring capabilities you require (examples below) and ensuring they are deployed and operating in those locations.

A strong SI-4(23) implementation is measurable (coverage, health, data flow), enforceable (baseline configs), and operational (alerts are triaged and drive response actions).

Plain-English interpretation

You must monitor your endpoints from the endpoint itself. Put sensors/agents/configurations on hosts so you can detect suspicious behavior and security-relevant changes even if network telemetry is incomplete, encrypted, or absent. Then prove the monitoring works: the agent is installed, configured to your standard, sending telemetry, generating alerts, and those alerts feed an accountable response process. ¹

Who it applies to (entity and operational context)

SI-4(23) commonly applies to:

• Federal information systems implementing NIST SP 800-53 controls. ²
• Contractor systems handling federal data where NIST SP 800-53 is flowed down contractually or used as the control baseline. ²

Operational contexts where SI-4(23) becomes “exam-critical”:

• Remote workforce with endpoints off-network.
• Cloud-heavy environments where east-west traffic visibility is limited.
• Encrypted traffic or privacy-driven limitations on deep packet inspection.
• High-privilege admin endpoints and production servers where host-level actions are the primary risk.

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

1) Name the control owner and the accountable operators

• Control owner (GRC): accountable for scope statement, mechanism list, and evidence plan.
• Endpoint engineering: accountable for packaging, deployment, configuration baselines.
• SOC / SecOps: accountable for alert ingestion, triage, tuning, incident workflow.
• IT operations: accountable for asset inventory alignment and device lifecycle controls.

Deliverable: a one-page SI-4(23) control implementation record that maps owner, scope, mechanism set, and recurring evidence. This aligns with the recommended best practice to map SI-4(23) to an owner, procedure, and artifacts. ¹

2) Define “locations” (scope) in operational terms

Write a scope statement that an engineer can implement and an auditor can test. Examples of location definitions:

• “All corporate-managed Windows/macOS workstations.”
• “All production Linux servers, including cloud instances in accounts X/Y.”
• “All endpoints that can access CUI repository systems” (if that’s your boundary concept).

Also document exclusions and compensating monitoring (if any): legacy systems, air-gapped hosts, specialized appliances. If you cannot run an agent, you still need a documented decision and an alternate monitoring approach, or a formal risk acceptance.

Evidence hook: a current endpoint inventory extract and a scoping rule (tags, OU, MDM group, cloud account list).

3) Define the required “mechanisms” by host class

Create a minimum mechanism baseline per endpoint type. Keep it short and testable. A practical baseline often includes:

• EDR/endpoint detection telemetry (process, command line, parent-child relationships).
• Anti-malware / exploit prevention policy and event logs.
• Host firewall / local security policy monitoring (configuration drift alerts).
• File integrity monitoring (FIM) for critical paths on servers where change control matters.
• Security log forwarding (Windows Event Logs, Linux audit logs) into your central monitoring.

You don’t need to list every feature your tool can do. List the mechanisms you require and how you will verify they are active (agent health, policy ID, event heartbeat, alert generation tests).

4) Standardize configuration and enforce it

• Define a gold configuration per host class (workstation, server, privileged endpoint).
• Use your endpoint management stack (MDM, configuration management, EDR policy) to enforce it.
• Control changes with tickets/approvals for exceptions, especially for:
  • Disabled protections
  • Reduced telemetry
  • “Silent mode” policies
  • Local admin overrides

Evidence hook: policy screenshots/exports, configuration baseline documents, change tickets for exceptions.

5) Prove telemetry flows to monitoring and response

SI-4(23) fails in practice when agents are deployed but don’t report.

• Confirm endpoints send telemetry to the central platform (SIEM/XDR/EDR console).
• Confirm alerts route into the SOC workflow (case management/ITSM).
• Confirm time synchronization and identity mapping (hostnames, device IDs) so alerts are actionable.

Evidence hook: sample alert-to-case chain, integration configuration, and a small set of representative endpoint event logs in the central repository.

6) Operationalize triage, tuning, and exceptions

Write a lightweight SOP that answers:

• Who triages host-based alerts, and what are the severity thresholds?
• What is the escalation path to incident response?
• How do you tune noisy detections without blinding coverage?
• How do you handle endpoints that are offline, unmanaged, or cannot run the tool?

Evidence hook: SOC runbooks, tuning records, exception register, and periodic health reports.

7) Make it auditable: define recurring evidence

Assessors look for repeatability. Set a recurring cadence for collecting:

• Coverage/agent health reports
• Policy compliance reports
• Alert and case metrics (counts are okay; avoid unsupported “success rate” claims)
• Exception and remediation tracking

If you use Daydream to manage third-party risk and control evidence, treat SI-4(23) like any other requirement: assign ownership, attach the procedure, then schedule evidence tasks that pull the same artifacts every cycle so audits become a packaging exercise instead of a fire drill.

Required evidence and artifacts to retain

Keep artifacts that prove design and operation:

Design evidence (what you intended):

• SI-4(23) scope statement: locations in scope and exclusions with rationale. ¹
• Mechanism baseline by host class (the organization-defined mechanisms). ¹
• Endpoint security architecture diagram (data flow from host to monitoring platform).
• SOP/runbook for host-alert triage and escalation.

Operational evidence (what actually happened):

• Agent deployment/coverage report by device group (export/screenshot + date).
• Agent health/heartbeat report (recent check-in proof).
• Policy compliance status (which endpoints have the correct configuration).
• Samples of security events/alerts from endpoints in the monitoring platform.
• Tickets/cases showing triage, investigation, containment, and closure.
• Exception register for devices that cannot meet the baseline, with approvals.

Common exam/audit questions and hangups

Auditors and assessors typically press on these points:

1. “What are your organization-defined locations?”
   If your answer is vague (“all endpoints”), expect follow-ups: which boundary, which inventory source, and how you validate completeness.

2. “What specific host-based mechanisms did you define?”
   Tool names are not mechanisms. Provide capability categories and the enforced settings.

3. “Show me coverage.”
   They may sample endpoints from inventory and ask you to prove an agent is installed, configured, and reporting.

4. “How do alerts get handled?”
   If alerts do not create tickets/cases, you’ll look “monitoring-only,” which is hard to defend for SI-4 in general.

5. “How do you manage exceptions?”
   Undocumented carve-outs are a recurring finding. Document, approve, and revisit.

Frequent implementation mistakes and how to avoid them

Mistake	Why it fails	Fix
Treating “EDR purchased” as compliance	Procurement is not operation	Require evidence: coverage, policy, reporting, triage workflow
Unscoped deployments	Leads to blind spots and untestable claims	Define locations using inventory-driven rules and exclusions
Inconsistent policies by team or region	Creates sampling failures	Enforce baselines per host class; track drift
Agents installed but not reporting	No monitoring data	Monitor agent health; alert on telemetry gaps
Exceptions handled in email/Slack	No durable record	Maintain an exception register with approvals and review triggers

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement, so you should treat SI-4(23) primarily as an assessment and authorization risk and a breach-impact amplifier. Practically, weak host-based monitoring increases dwell time risk and reduces your ability to prove containment and root cause because you lack endpoint evidence. That translates into harder incident response, weaker reporting, and higher contractual risk if you handle federal data under a NIST-aligned requirement set. ²

A practical 30/60/90-day execution plan

First 30 days (establish decisions and scope)

• Assign SI-4(23) control owner and operator owners (endpoint + SOC).
• Draft “organization-defined locations” and validate against your endpoint inventory.
• Draft “organization-defined mechanisms” by host class and confirm tool support.
• Decide how you will evidence operation (reports, exports, ticket samples).
• Create an exception intake process (ticket type + approval path).

Days 31–60 (deploy, standardize, connect)

• Roll out agents/policies to the highest-risk endpoint groups first (privileged endpoints, production servers).
• Implement and test telemetry flow to your monitoring platform.
• Stand up agent health monitoring and failure alerts.
• Publish SOC triage runbook for endpoint alerts; train the on-call rotation.
• Start collecting recurring evidence in a central repository (or in Daydream control tasks).

Days 61–90 (prove operation and harden)

• Run a controlled detection test (benign) to confirm alerts, ticketing, and escalation work end-to-end; retain artifacts.
• Tune top noisy detections with documented rationale and approvals.
• Reconcile inventory vs. agent coverage; close gaps with remediation tickets.
• Review exceptions; convert long-term exceptions into formal risk acceptances or decommission plans.
• Prepare an audit packet: scope, mechanism baseline, coverage/health reports, alert-to-case examples.

Frequently Asked Questions

What counts as a “host-based monitoring mechanism” for SI-4(23)?

SI-4(23) lets you define the mechanisms, but they must be host-resident capabilities that generate monitoring telemetry or detection signals from the endpoint itself. Document the mechanism categories you require and show they are deployed and operating. ¹

Can we meet SI-4(23) with only a SIEM and network IDS?

Usually no, because SI-4(23) explicitly requires host-based mechanisms at defined locations. A SIEM can be the collection point, but you still need endpoint sensors and host log sources feeding it. ¹

How do we handle endpoints that can’t run an agent (legacy, appliances, OT)?

Put the exclusion in writing, get an approval, and document the alternate monitoring or compensating controls you will use. Keep an exception register and revisit it as part of lifecycle management. ¹

What evidence is most persuasive to an assessor?

Coverage and health reporting tied to an authoritative inventory, plus a small set of alert-to-case examples that show detection and response actually happened. Pair that with your written scope and mechanism baseline. ²

Do we need the same mechanisms on workstations and servers?

Not necessarily. Define mechanisms by host class and risk, then enforce those baselines consistently within each class. The key is that your “organization-defined mechanisms” are explicit and testable. ¹

How should a GRC team operationalize SI-4(23) without owning endpoint tools?

Own the decisions and evidence: scope, mechanism baseline, exception process, and recurring evidence schedule. Endpoint and SOC teams run the tooling, but GRC ensures the requirement remains testable and continuously evidenced, which is where platforms like Daydream help. ¹

Footnotes

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

2. NIST SP 800-53 Rev. 5