SI-4(24): Indicators of Compromise

SI-4(24) requires you to consistently discover, collect, and distribute indicators of compromise (IOCs) from your approved sources to the teams and systems that need them, fast enough to improve detection and response. Operationalize it by defining IOC sources and recipients, standardizing formats and workflow, and keeping evidence that IOCs were ingested, routed, and acted on. ¹

Key takeaways:

• Define approved IOC sources and intended recipients, then document the routing and handling rules. ¹
• Build an intake-to-distribution workflow that is measurable: what came in, where it went, and what systems applied it. ²
• Retain evidence of both design (procedure, roles) and operation (tickets/logs/feeds, change records, exceptions). ²

The si-4(24): indicators of compromise requirement is a narrow enhancement under SI-4 (System Monitoring), but it creates a frequent audit gap because teams “get threat intel” informally without proving consistent distribution and use. SI-4(24) is not asking you to invent IOCs; it expects you to take IOCs provided by defined sources and get them to the defined consumers in your organization so they can improve monitoring, detection, and response. ¹

For a Compliance Officer, CCO, or GRC lead, the fastest path is to treat SI-4(24) like an operational supply chain: upstream producers (who provides IOCs), a controlled intake process (how you receive, validate, and normalize), distribution channels (who receives and how), and downstream confirmation (where the IOC was applied and what happened). You should be able to answer, on demand: “Which IOC sources do we trust, where do their indicators go, and how do we prove it happened?” ²

This page gives requirement-level implementation guidance you can hand to a SOC lead, detection engineer, or IR manager and then audit with confidence.

Regulatory text

Requirement: “Discover, collect, and distribute to [defined recipients], indicators of compromise provided by [defined providers].” ¹

Operator translation (what you must do):

1. Identify IOC providers you will rely on (internal and external).
2. Discover and collect IOCs from those providers through a repeatable process (feeds, reports, incident outputs, coordination channels).
3. Distribute the IOCs to the recipients that need them (people and/or systems), using defined channels and formats.
4. Prove operation with records showing intake, handling, dissemination, and downstream application. ¹

This enhancement is simple on paper, but assessors will test whether your distribution is real, timely in practice, and reaches the systems that actually detect and block threats.

Plain-English interpretation of SI-4(24)

SI-4(24) expects a working loop between threat intelligence and security operations. If you receive indicators (IPs, domains, file hashes, URLs, email sender artifacts, YARA/Sigma-like patterns, cloud resource identifiers, or behavior-based detections), you need a controlled way to:

• ingest them,
• verify/normalize them,
• route them to the right places,
• and track whether they were deployed or consumed.

The control’s center of gravity is distribution. Many programs can show they “subscribe” to intel, but cannot show which indicators were shared with endpoint tooling, network security, SIEM correlation, email security, cloud controls, or incident response playbooks. ²

Who it applies to

Entity scope

• Federal information systems and contractor systems handling federal data, where NIST SP 800-53 Rev. 5 is the governing control set. ²

Operational context

• SOC and security monitoring programs that run a SIEM, EDR, NDR, email security gateway, WAF, CASB/SSE, cloud security tooling, or managed detection and response.
• Incident response teams that generate IOCs during investigations and need to push those indicators back into monitoring and prevention controls.
• GRC teams that must demonstrate that monitoring is informed by external and internal threat information, with traceable evidence.

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

Step 1: Define IOC providers and recipients (make it auditable)

Create a short “IOC Distribution Register” with:

• IOC providers (examples: internal IR cases, SOC investigations, threat intel provider, ISAC/ISAO, government/sector alerts, MSSP).
• Recipients by function and system: SIEM content team, EDR admin, firewall team, email security admin, cloud security, vulnerability management, fraud/abuse team (if applicable).
• Distribution channel for each recipient: ticket queue, automated feed into a platform, approved chat channel with retention, email to a distribution list with archiving, or a SOAR action.
• Handling rules: accepted indicator types, required context fields, confidence thresholding, and who can approve “block” vs “detect-only.” ¹

Deliverable: a one-page standard plus a table. Keep it lean; assessors prefer clarity over prose.

Step 2: Build the intake pipeline (discover + collect)

You need an intake mechanism that does not depend on a single person’s inbox. Common patterns:

• Threat intel feed ingestion into TIP/SIEM/SOAR.
• Case-driven extraction: analysts tag observables in investigations; a review step promotes them to “candidate IOCs.”
• Third-party notifications: customer/partner abuse reports or hosting provider notices go into a queue with triage.

Minimum operational requirements:

• Central inbox/queue for IOC submissions (ticketing system works).
• Normalization: consistent fields (type, value, source, first-seen, confidence, context, expiration/TTL, intended action).
• Deconfliction and dedupe.
• A decision point: publish, publish with restrictions, or reject. ²

Step 3: Distribute to the right places (and prove it)

Distribution must be purpose-built, not “we posted it somewhere.”

Use a distribution matrix like this:

Recipient	IOC types needed	Delivery method	Expected action	Proof artifact
EDR admin/team	hashes, domains, process traits	automated push or ticket	add to block/detect list	change record + EDR audit log
Network/security gateway	IPs, domains, URLs	firewall/DNS policy ticket	block/alert	ticket + policy commit log
SIEM detection team	patterns, correlation inputs	content backlog item	new rule / add enrichment	PR/commit + rule deployment
IR team	any	case link	hunting + scoping	case notes + hunt results

Your proof should show: IOC received → evaluated → distributed → applied. Even if some recipients only “hunt” (no blocking), you still need the evidence trail. ¹

Step 4: Add governance controls that prevent bad indicators from causing outages

SI-4(24) creates operational risk if teams push low-quality IOCs into blocking controls.

Add guardrails:

• Approval for “block” actions (two-person review for high-impact controls).
• Expiration/TTL policy (I’m giving a concept, not a required timeframe): indicators should not live forever without revalidation.
• Exception path for business-critical false positives, with documentation.
• Source reliability tagging and confidence scoring conventions. ²

Step 5: Measure and review (keep it assessable)

Define internal KPIs as management metrics, not regulatory facts:

• Volume of IOCs ingested by source
• Distribution coverage across key security control points
• Backlog age for unreviewed IOCs
• False-positive/rollback counts for blocked indicators

Then run a recurring review with SOC + GRC:

• Are the providers still relevant?
• Are indicators reaching the systems that matter?
• Are there recurring failures (format issues, missing context, ownership gaps)? ²

Required evidence and artifacts to retain

Assessors commonly ask for both “design” and “operating” evidence. Retain:

Design evidence

• SI-4(24) procedure (1–3 pages) describing discover/collect/distribute workflow. ²
• IOC Distribution Register (providers, recipients, channels, handling rules). ¹
• Roles and ownership (RACI) for intake triage, approval, and publication. ²

Operating evidence

• Samples of IOC intake items (tickets/records) showing source and context.
• Distribution records (SOAR run logs, email archives, chat export with retention, ticket assignments).
• Downstream application proof (EDR policy logs, firewall change commits, SIEM content deployment PRs).
• Exceptions/false positive rollbacks with rationale and approvals.
• Periodic review notes/minutes and resulting action items. ²

Tip: Evidence sampling should show multiple sources and multiple recipients, not one happy-path example.

Common exam/audit questions and hangups

Expect these questions:

1. “Who provides your IOCs?” Name sources and show the register. ¹
2. “Who receives them?” Show the distribution matrix and ownership. ¹
3. “Prove distribution.” Provide a trace from intake record to downstream system change/log. ²
4. “How do you prevent bad blocks?” Show approvals, testing, and rollback process. ²
5. “Is this consistent or ad hoc?” Demonstrate recurring operation via logs/tickets and review cadence. ²

Audit hangup: if your “distribution” is a static wiki page, you will struggle to show controlled dissemination and consumption.

Frequent implementation mistakes (and how to avoid them)

1. Mistake: Treating subscription as compliance. A feed subscription without ingestion and routing evidence fails the “distribute” expectation.
   Avoid: keep ingestion logs and downstream delivery records. ¹

2. Mistake: No defined recipients. “SOC gets it” is not specific enough.
   Avoid: list recipients by team and by control point (EDR, firewall, SIEM, email, cloud). ¹

3. Mistake: IOC dumping without context. Raw hashes without source, confidence, and first-seen lead to poor actions and false positives.
   Avoid: require a minimum context schema and reject incomplete submissions. ²

4. Mistake: No lifecycle management. Indicators persist after they are stale, causing alert fatigue and blocking errors.
   Avoid: define review/expiration rules and show they operate (exception logs help). ²

5. Mistake: Evidence scattered across tools. You can’t reconstruct the chain during an assessment.
   Avoid: map SI-4(24) to an owner and a recurring evidence bundle; Daydream is often used to keep the procedure, register, and evidence samples packaged for audits without rebuilding the story each cycle. ²

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for SI-4(24), so treat this as an assessment and contractual compliance risk rather than a control with a specific cited penalty event in this dataset. ¹

Operational risk is still real:

• Poor distribution means known bad infrastructure and artifacts are not reflected in monitoring and prevention controls.
• Over-aggressive distribution without governance can create self-inflicted outages through false-positive blocks. Your objective is balanced: fast routing with controlled decisioning. ²

Practical 30/60/90-day execution plan

Days 0–30: Establish the minimum viable SI-4(24) program

• Assign a control owner (SOC manager or detection engineering lead) and a GRC co-owner for evidence quality.
• Publish the IOC Distribution Register (providers, recipients, channels, handling rules).
• Stand up a single intake queue and define required fields.
• Pick two downstream destinations to prove end-to-end distribution (commonly SIEM + EDR) and run the workflow with real samples.
• Start an evidence folder structure: design docs + operating samples, aligned to SI-4(24). ¹

Days 31–60: Expand coverage and add guardrails

• Add remaining recipients (network controls, email security, cloud controls) into the matrix.
• Implement approval and rollback process for block actions; document decision authority.
• Normalize formats (CSV/JSON templates, ticket forms, or SOAR objects) so ingestion and routing are consistent.
• Run a tabletop review of a “bad IOC” scenario and verify the exception path produces auditable records. ²

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

• Operationalize recurring review meetings with minutes and action items.
• Build a standard assessment packet: last period’s IOC samples, distribution proofs, exceptions, and review notes.
• Validate that each provider has at least one demonstrated intake-to-distribution chain in your evidence.
• If you use Daydream, map SI-4(24) directly to the owner, procedure, and recurring artifacts so evidence collection becomes a scheduled task instead of a scramble. ²

Frequently Asked Questions

What counts as an “indicator of compromise” for SI-4(24)?

Treat IOCs as actionable observables tied to malicious activity, such as IPs, domains, URLs, file hashes, and detection patterns, when your program can distribute and apply them. Keep the definition you use in your procedure so auditors see consistent handling. ²

Do we need a Threat Intelligence Platform (TIP) to satisfy SI-4(24)?

No tool is mandated by the requirement text. You do need a repeatable way to collect and distribute IOCs with evidence, which can be done with ticketing and logs if it’s controlled and consistent. ¹

How do we prove “distribution” in an audit?

Provide an end-to-end chain: IOC intake record from an approved source, distribution event to a named recipient/channel, and downstream application evidence such as policy change logs or detection content deployment records. ²

What if we receive IOCs that we decide not to deploy?

Keep the decision record and rationale (for example, low confidence, not relevant to your environment, known false positive). Auditors mainly want to see that you consistently triage and that distribution rules are followed. ²

How do internal IOCs from incident response fit into SI-4(24)?

Internal investigations are valid providers if you define them as such and your workflow collects and distributes the resulting IOCs back into monitoring and preventive controls. Keep case references and promotion records as evidence. ¹

We outsource monitoring to a third party. Are we still on the hook?

Yes, you still need to ensure IOCs are collected and distributed to the parties that perform monitoring and response for your environment. Contractual requirements and shared evidence (tickets, reports, feed logs) are how you show the control operates. ²

Footnotes

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

2. NIST SP 800-53 Rev. 5