AC-4(15): Detection of Unsanctioned Information

AC-4(15) is a focused enhancement under the NIST 800-53 Access Control family that targets one high-risk moment: when information crosses from one security domain to another. “Security domains” can mean networks (classified/unclassified, corporate/production), environments (dev/test/prod), tenants, enclaves, or any boundary where different security policies apply. If you allow data to cross those boundaries without inspection, you are effectively trusting that users, apps, and third parties will never move restricted content the wrong way.

This requirement is not a generic “monitor the network” statement. It expects two things that you can operationalize quickly: (1) you define what counts as unsanctioned information for your organization and (2) you implement a mechanism that examines transfers and prohibits them when unsanctioned content appears, aligned to written criteria.

For a Compliance Officer, CCO, or GRC lead, success looks like: clear scoping of cross-domain flows, a control owner with runbooks, enforced technical gates (not just policy), and a tight evidence package that an assessor can verify without guesswork.

Regulatory text

Requirement (excerpt): “When transferring information between different security domains, examine the information for the presence of {{ insert: param, ac-04.15_odp.01 }} and prohibit the transfer of such information in accordance with the {{ insert: param, ac-4.15_prm_2 }}.” ¹

Operator translation of the placeholders: The control is parameterized. You must (a) specify the categories/patterns that represent unsanctioned information for your environment and (b) specify the rules/conditions that determine when a transfer must be blocked (for example, “block when sensitive data is detected,” “block unless an approved release is attached,” or “block when destination domain is lower trust”). Your implementation has to follow your defined parameters, not ad hoc judgments. ¹

Plain-English interpretation (what the control is really asking)

You must treat cross-domain transfers as a controlled checkpoint:

1. Inspect the content (not only metadata) moving between domains.
2. Detect unsanctioned content as you defined it (examples: controlled unclassified information, export-controlled content, certain PII elements, proprietary source code, secrets, malware, or unapproved file types).
3. Stop the transfer when prohibited content is present, based on your documented criteria.

This is a prevention-oriented requirement. Logging alone is useful, but the requirement explicitly calls for prohibiting transfer when the criteria are met. ²

Who it applies to (entity and operational context)

Entity types

• Federal information systems
• Contractor systems handling federal data ¹

Operational contexts where assessors expect you to apply it

• Cross-domain gateways (high-to-low / low-to-high transfers)
• Network segmentation boundaries (corporate ↔ production; IT ↔ OT)
• Cloud boundaries (tenant-to-tenant, account-to-account, subscription-to-subscription)
• Email and collaboration sharing across domains (external sharing, B2B tenants)
• File transfer channels (SFTP, managed file transfer, object storage replication)
• CI/CD promotion paths (build artifacts from dev into prod; code export to external repos)

If your system boundary includes third parties (managed SOC, MSP, SaaS admins, offshore development), treat any data movement into their domain as a cross-domain transfer scenario when security policy differs.

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

Step 1: Define your parameters (what is “unsanctioned,” and what gets blocked)

Create a short, enforceable “Unsanctioned Information Detection Standard” that includes:

• Unsanctioned content definitions: data types, labels, patterns, file types, classifications, and known high-risk repositories.
• Blocking criteria: the conditions that trigger a hard block vs quarantine vs require approval.
• Allowed transfer conditions: exceptions such as “approved release package,” “tokenized data only,” “encrypted with approved key and recipient,” or “destination is approved partner enclave.”
• False-positive handling: who can override, under what approvals, with what logging.

This is the heart of the placeholders in the control text. Your tooling configuration must map directly to these definitions. ¹

Step 2: Inventory every cross-domain transfer path (the “choke points”)

Build a simple register (spreadsheet is fine) listing:

• Source domain, destination domain
• Transfer mechanism (API, email gateway, proxy, MFT, storage replication, endpoint sync)
• Data types commonly transferred
• Current inspection point (if any) and current enforcement mode (block/alert/allow)
• Control owner and supporting team (network, cloud, endpoint, app)

Common hangup: teams document one “official” gateway and miss shadow paths such as admin backdoors, direct cloud sharing, and third-party connectors.

Step 3: Place inspection and blocking controls at each path

Pick the control mechanism that actually sits inline or can stop the transfer for that channel:

• Network / gateway paths: secure web gateway, CASB inline controls, firewall content inspection, cross-domain solutions where applicable.
• Email and collaboration: DLP policies on outbound mail and external sharing controls.
• Endpoints: endpoint DLP for copy to USB, browser uploads, sync clients.
• Cloud storage: object storage policies, DLP scanning + quarantine workflows, sharing restrictions.
• APIs and app-to-app flows: API gateways with content validation, egress controls, and policy enforcement where feasible.

The compliance test: “Show me where the transfer is examined, and show me how you prevent it when the rule triggers.” ²

Step 4: Align enforcement actions to the written criteria

Your prevention outcomes should be deterministic:

• Block and notify user + security
• Quarantine for review (if your criteria allows conditional release)
• Route to an approved sanitization/redaction workflow
• Require a tracked approval ticket before reattempting transfer

Avoid “security analyst decides in Slack.” If you need human review, formalize it as an exception workflow with required fields and approvals.

Step 5: Test detection and block behavior with representative samples

Create a test suite that covers:

• True positives (content that must be blocked)
• Expected negatives (content that must pass)
• Edge cases (compressed files, encrypted archives, images with embedded text, code snippets)

Record test case IDs, inputs, expected outcomes, and actual outcomes. Re-run after major policy changes and after tooling updates.

Step 6: Monitor and tune (without weakening the requirement)

Run a tuning cycle:

• Review false positives and update patterns carefully
• Add missing detectors when incidents or near-misses appear
• Ensure exceptions do not become a permanent “allow list” that bypasses inspection

Step 7: Make it assessable: control ownership, procedure, recurring evidence

Assign a named owner and publish a short runbook:

• Where the inspection points are
• How blocking rules are implemented
• How alerts are triaged
• How exceptions are approved
• What evidence is collected on a schedule

Daydream fits naturally here as the system of record to map AC-4(15) to an owner, procedure, and recurring evidence artifacts so you can answer assessor questions with a single control packet instead of hunting across teams. ¹

Required evidence and artifacts to retain (assessor-ready)

Keep artifacts that prove (a) scope, (b) configuration, and (c) operation:

Governance

• Unsanctioned Information Detection Standard (definitions + blocking criteria)
• Data classification / handling policy references (only what’s needed to interpret “unsanctioned”)
• Exception process and approval matrix

Technical implementation

• Architecture diagram marking security domains and transfer paths
• Configuration exports or screenshots of DLP/content inspection rules
• Rule-to-requirement mapping (which rule implements which unsanctioned category)

Operational records

• Samples of blocked transfer logs (with timestamps, rule IDs, action taken)
• Incident or ticket records for confirmed events and exceptions
• Test plan + test results showing blocks and allowed transfers
• Change records for rule updates (who approved, what changed, why)

Common exam/audit questions and hangups

Assessors commonly press on:

• “Define ‘security domain’ in your environment. Show boundaries.”
• “Where exactly do you examine content during transfer?”
• “Does the control block or only alert? Show evidence of prohibition.” ¹
• “How did you choose what counts as unsanctioned information?”
• “How do exceptions work, and how do you prevent exception abuse?”
• “Show tests that prove the rule works after updates.”

Hangup to expect: teams confuse general DLP monitoring with cross-domain enforcement. AC-4(15) is about transfers between domains and requires blocking per defined criteria.

Frequent implementation mistakes (and how to avoid them)

1. Unclear definition of “unsanctioned.”
   Fix: write explicit categories and patterns; tie each to a blocking rule.

2. Gaps in transfer-path inventory.
   Fix: include third-party connectors, cloud sharing links, sync clients, admin tools, and CI/CD artifact promotion.

3. Alert-only mode left on indefinitely.
   Fix: define a timeline to move high-confidence detections to block, with documented risk acceptance for any channel that cannot block.

4. Overbroad exceptions that bypass inspection.
   Fix: exceptions should be time-bound, scoped to a path or dataset, and logged with an approver.

5. No regression testing after rule changes.
   Fix: maintain a small set of representative test files and re-run tests after policy/tool updates.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this specific enhancement, so you should treat it as an assessment and risk-management expectation rather than a case-law-driven requirement. The practical risk is straightforward: unsanctioned content crossing into a lower-trust domain can create reportable incidents, contract noncompliance for federal data handlers, and loss of control over sensitive information. ²

Practical 30/60/90-day execution plan

Use phases rather than day-count promises; your tooling and domain complexity will drive sequencing.

First 30 days (Immediate)

• Assign control owner and supporting technical owners per transfer channel.
• Draft the parameter definitions: unsanctioned categories and blocking criteria. ¹
• Build the cross-domain transfer-path register and identify top-risk paths (external sharing, email, MFT, production egress).

Days 31–60 (Near-term)

• Implement inspection and blocking on the highest-risk paths where you can enforce inline decisions.
• Stand up exception workflow with approvals and logging.
• Create initial test suite; run tests and capture results for evidence.

Days 61–90 (Stabilize and expand)

• Expand coverage to remaining transfer paths and refine detections.
• Move mature detections from alert to block where risk warrants.
• Package evidence into an assessor-ready control file (policy, diagrams, configs, logs, tests, exceptions). Daydream can host the control narrative and recurring evidence checklist so audits become repeatable instead of bespoke. ¹

Frequently Asked Questions

What counts as a “security domain” for AC-4(15)?

Treat any boundary where different security policies apply as a different domain (separate networks, cloud accounts, tenants, enclaves, or environments). Document your domain model and show where transfers cross those boundaries. ²

Do we have to block every detection event?

The control text requires you to “prohibit the transfer” according to your defined criteria, so the key is that your written rules specify what must be blocked and your system enforces it. If some channels can only alert, document compensating controls and risk acceptance. ¹

Can we satisfy AC-4(15) with endpoint DLP alone?

Only if endpoint DLP truly covers the cross-domain transfer paths in scope and can prevent the transfer according to your criteria. Many organizations still need gateway/cloud controls for email, web, and SaaS sharing.

How do we handle encrypted files or password-protected archives?

Define a rule for “uninspectable content” as unsanctioned for certain transfers, or require approved encryption and key exchange conditions. Then enforce the rule consistently at the transfer point and log blocks and exceptions.

What evidence do assessors ask for most often?

They usually ask for proof of enforcement: configurations showing inspection rules, logs showing blocked transfers, and test results demonstrating the behavior. Keep a clean mapping from your definitions to the implemented rules. ¹

Where does this overlap with other controls?

AC-4(15) is narrowly about cross-domain flow inspection and prohibition. You’ll usually pair it with broader information flow enforcement (AC-4), monitoring and event handling, and data protection controls, but AC-4(15) needs its own scoped transfer-path and evidence package. ²

Footnotes

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

2. NIST SP 800-53 Rev. 5