SI-3(8): Detect Unauthorized Commands

SI-3(8) is a narrow enhancement with a sharp technical expectation: you are not simply “logging admin activity.” You are detecting specific unauthorized OS commands by observing execution through the kernel application programming interface on a defined set of systems. That means your control design has to answer two questions cleanly: (1) what commands are unauthorized in your environment, and (2) how do you detect their execution in a way an attacker cannot easily bypass by avoiding the shell or tampering with user-space logs.

For a Compliance Officer, CCO, or GRC lead, the fastest path is to treat SI-3(8) like a requirement you can map to a measurable control statement: “For all in-scope endpoints and servers, we detect execution of prohibited commands at the kernel telemetry layer, alert on events, and investigate per IR procedures.” Your job is to make that statement true operationally, provable to an assessor, and sustainable for operations.

This page gives requirement-level implementation guidance you can hand to endpoint security, SecOps, and platform teams, plus the artifacts you need to retain for audit readiness aligned to NIST SP 800-53 Rev. 5. ¹

Regulatory text

Excerpt (as published): “Detect the following unauthorized operating system commands through the kernel application programming interface on [assignment: organization-defined system components]: [assignment: organization-defined unauthorized operating system commands]; and” ²

What this means for an operator

You must:

1. Name the system components where this applies (your “in-scope” assets).
2. Define the unauthorized OS commands (the prohibited command list).
3. Detect execution via kernel API visibility, not only via user-space artifacts (e.g., bash history, PowerShell transcripts, or application logs).
4. Produce and handle detections (alerts/events) so you can demonstrate the control operates, not just exists.

Because the control text uses organization-defined parameters, assessors will focus on whether your definitions are defensible and whether detection is real at the kernel telemetry layer, not easily bypassed. ²

Plain-English interpretation

SI-3(8) requires you to catch command execution that your organization has explicitly prohibited, using telemetry that observes the operating system at or near the kernel boundary. In practice, this commonly maps to endpoint detection and response (EDR) sensor telemetry, kernel/audit subsystem events, or OS security providers that report process creation and privileged operations in a tamper-resistant way.

Your “unauthorized commands” are usually commands that:

• enable credential theft or persistence,
• disable security controls,
• modify audit logging,
• create new privileged accounts,
• perform sensitive network pivoting or remote execution outside approved tooling,
• or run administrative shells where they are not allowed.

The control does not dictate the exact list. It requires that you define it, detect it at the kernel API layer on the systems you declare in scope, and operationalize response and evidence.

Who it applies to

Entity scope

• Federal information systems and contractor systems handling federal data implementing NIST SP 800-53 Rev. 5 controls. ¹

Operational scope (where the control is typically assessed)

• Servers and endpoints where OS command execution occurs: Linux, Windows, and container hosts.
• High-risk administrative planes: domain controllers, identity systems, bastion hosts, CI/CD runners, build servers, database servers.
• Workloads managed by third parties (cloud-managed servers, MDR-covered endpoints) if they are within your authorization boundary; treat the provider as a third party and contract for the telemetry and evidence you need.

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

Step 1: Set ownership and write a measurable control statement

• Assign a control owner (often Endpoint Security or SecOps) and a GRC owner responsible for evidence and assessment coordination.
• Write a testable statement:
  • “We detect execution of prohibited OS commands on in-scope systems using kernel-level telemetry, generate alerts to SecOps, and investigate per incident procedures.”

This is the “north star” for your runbooks and evidence.

Step 2: Define “in-scope system components” (the coverage boundary)

Create an asset scoping rule that an assessor can follow:

• Which environments: production, corporate endpoints, privileged admin workstations, staging.
• Which platforms: Windows, Linux, container hosts, VDI.
• Which exceptions exist and why (legacy OS, air-gapped, embedded).

Deliverable: a coverage matrix (system component category → telemetry method → logging destination → alerting path).

Step 3: Define the “unauthorized OS commands” list

Work with SecOps and platform owners to define an initial list based on your environment and threat model. Make it enforceable:

• Use command families and high-risk arguments where needed (e.g., “any command that disables host firewall”).
• Separate by OS:
  • Windows examples: local user creation, security product stoppage, suspicious PowerShell invocation patterns, service creation commands.
  • Linux examples: audit/log tampering, kernel module insertion, credential dumping tools, suspicious network tunneling binaries.

Practical guardrail: include an approval process for changes to the prohibited list (change ticket + security sign-off). That prevents the list from drifting or becoming unmaintainable.

Step 4: Implement kernel-layer detection

Your technical team must choose a method that credibly observes command execution through kernel interfaces. Common implementation patterns:

• EDR sensor with kernel telemetry generating process execution events and command-line parameters.
• OS auditing frameworks (e.g., Linux audit subsystem, Windows security auditing) forwarded to a centralized SIEM, with detection rules.
• Kernel-event based security agents in hardened configurations to reduce tampering.

What assessors look for is not the brand. It’s whether the signal is:

• present on in-scope systems,
• sufficiently detailed to identify the prohibited command,
• protected from easy bypass (user-space only logging is a red flag),
• centrally collected and monitored.

Step 5: Turn detections into alerts with defined triage outcomes

Create a small set of alert use cases aligned to the prohibited list:

• Alert name, severity, routing, and expected response time (your policy choice).
• Triage steps: validate host, user, parent process, command-line, hash, network connections.
• Containment options: isolate host, disable account, block hash, revoke session.

Tie the triage to incident handling procedures already in place to avoid inventing a parallel process.

Step 6: Prove operational monitoring (not “set and forget”)

Define recurring operational checks:

• Sensor coverage checks (missing agents, stale logs).
• Rule health checks (noisy rule tuning, false positive handling).
• Quarterly or event-driven review of the prohibited command list (after major OS changes or incidents).

Step 7: Build assessor-ready evidence packaging

Create a single “SI-3(8) evidence pack” folder and keep it current. That reduces scramble during audits and helps you delegate collection.

Required evidence and artifacts to retain

Keep artifacts that prove definition, implementation, and operation:

1. Control narrative / procedure
   • Control statement, scope definition, roles, and workflow.
2. Unauthorized command list
   • Version-controlled list with approval history (change tickets or pull requests).
3. Coverage matrix
   • Systems/components in scope and how kernel-level telemetry is collected.
4. Tool configuration evidence
   • Screenshots or exports of sensor deployment status, audit policy settings, SIEM ingestion configuration, and detection rules.
5. Detection output samples
   • Redacted alert examples showing command, host, user, timestamp, and response actions.
6. Triage runbook
   • Documented steps and escalation path.
7. Recurring review records
   • Meeting notes, tickets, or attestations showing periodic verification and tuning.

A common risk factor is simply failing to keep evidence that the control is operating consistently. ²

Common exam/audit questions and hangups

Assessors and auditors tend to probe these points:

• “Show me your organization-defined unauthorized commands.” If you cannot produce a list, you fail the definition step. ²
• “How do you know this is kernel-level detection?” Be ready to explain the telemetry source and why it is not just shell logs.
• “Which systems are in scope, and how do you prove coverage?” Expect a sampling exercise: they will pick a host and ask for telemetry proof.
• “What happens when a prohibited command is detected?” You need a triage path with tickets or case management evidence.
• “How do you tune false positives without weakening detection?” Show rule change control and rationale.

Frequent implementation mistakes (and how to avoid them)

Mistake	Why it fails	Fix
Using only shell history / script logs	Attackers can bypass or tamper with user-space artifacts	Use EDR/audit telemetry that reports process execution at the OS boundary and forward centrally
Defining “unauthorized commands” as a vague category	Control requires organization-defined commands; vague lists are not testable	Maintain a specific, versioned list with examples and patterns
No coverage proof	You cannot show sensors/audit policy are deployed everywhere claimed	Keep a live coverage matrix and periodic deployment reports
Alerts without response	Detection exists on paper, but operations ignore it	Route alerts to SecOps queue and track case outcomes
Over-broad prohibited list that floods alerts	Teams disable rules under pressure	Start with high-signal commands, tune, then expand

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for SI-3(8). Your risk exposure is still practical and material: prohibited command execution is a common precursor to privilege escalation, persistence, and defense evasion. If you cannot detect these actions, incident response becomes slower and less reliable, and an assessor can reasonably conclude you lack visibility into high-impact malicious activity. ¹

Practical 30/60/90-day execution plan

Use this as an execution scaffold; adjust the pace to your environment and change control requirements.

First 30 days (define + scope + pick telemetry path)

• Confirm control owner and stakeholders (Endpoint, SecOps, platform, GRC).
• Draft the in-scope system component list and exceptions.
• Publish v1 of the unauthorized command list (Windows and Linux separated).
• Choose the kernel-telemetry collection method already approved in your environment (EDR, OS audit, or both).
• Create the SI-3(8) evidence pack structure and naming conventions.

Days 31–60 (implement + alerting + initial evidence)

• Deploy/validate sensors or audit configuration on in-scope systems.
• Build detections and alert routing to the SOC (ticketing integration where possible).
• Run controlled tests (approved security testing) to generate sample detections.
• Write the triage runbook and escalation matrix.
• Capture first operational evidence: coverage report, rule exports, sample alerts, triage ticket.

Days 61–90 (stabilize operations + governance)

• Tune rules based on false positives; document every material rule change.
• Implement a recurring review cadence for the prohibited command list and coverage checks.
• Add metrics that are easy to evidence without inventing numbers: “alerts reviewed,” “cases opened,” “exceptions granted.”
• Conduct a tabletop review with SecOps and GRC: walk one detection from event to closure and confirm artifacts are retained.

How Daydream helps (without changing your tools)

Most SI-3(8) failures are evidence and ownership failures, not a missing product. Daydream can act as the control system of record: map SI-3(8) to a named owner, store the prohibited command list and coverage matrix, schedule recurring evidence requests, and package artifacts for assessors so you can prove operation without rebuilding your security stack. ²

Frequently Asked Questions

Do I have to detect every possible malicious command?

No. SI-3(8) requires detection of the organization-defined unauthorized OS commands on organization-defined system components. The key is that your defined list is defensible and your detection reliably covers the scope you claim. ²

Does PowerShell script logging count as “kernel API” detection?

Script logging is valuable but is typically user-space. For SI-3(8), be prepared to show process execution and command-line visibility from a kernel-adjacent telemetry source (for example, EDR process creation events or OS audit events) aligned to the control text. ²

How do we handle managed endpoints where a third party runs the EDR?

Treat it as a third-party dependency and require contractually that the provider supplies coverage proof, detection rule details (as allowed), and alert/ticket evidence. Your assessor will still expect you to demonstrate the control operates for in-scope systems.

What’s the minimum evidence an auditor will accept?

Expect to provide (1) your prohibited command list, (2) proof of kernel-level telemetry coverage on sampled systems, (3) detection/alert samples, and (4) a runbook or ticket showing triage occurred. ²

Our environment is container-heavy. What counts as “operating system commands”?

Focus on where the command executes and where you can observe it through kernel-level telemetry: container host process execution, container runtime operations, and privileged container activity are common scoping targets. Document your scoping logic so an assessor can follow it.

How often should the unauthorized command list be updated?

Update it when threat tradecraft changes for your environment, when platforms change, and after incidents or tests reveal gaps. Tie updates to change control so you can show who approved changes and why.

Footnotes

1. NIST SP 800-53 Rev. 5

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