AC-19(3): Use of Portable Storage Devices with No Identifiable Owner

AC-19(3) requires you to prevent use of portable storage devices that have no identifiable owner (for example, untagged USB drives) on systems in scope, or tightly control their use through documented handling, scanning, and accountability. Operationalize it by enforcing technical blocks where possible, defining an exception workflow, and retaining logs that prove detection and response. ¹

Key takeaways:

• Treat “no identifiable owner” media as untrusted by default; block or quarantine it at the endpoint and at intake points. ¹
• Make accountability provable: asset identification, check-in/check-out, and event logs that link the device to a person and approval. ²
• Auditors will ask for evidence of enforcement, not policy text; build recurring artifacts and an exception trail. ¹

AC-19 is the NIST 800-53 access control family’s portable storage media requirement set. Enhancement (3), “Use of Portable Storage Devices with No Identifiable Owner,” is narrowly scoped but operationally sharp: a USB stick, SD card, or external drive with unknown provenance is a common path for malware introduction and data loss, and it breaks basic accountability. Your job as a CCO/GRC lead is to turn that concept into repeatable controls that security operations can enforce and auditors can test.

This page translates the ac-19(3): use of portable storage devices with no identifiable owner requirement into a practical control design: define what “identifiable owner” means in your environment, implement technical restrictions (endpoint/device control, OS policies, EDR rules, and intake scanning), and create an exception process for legitimate business needs. You will also need evidence that the controls run continuously, that exceptions are rare and approved, and that violations trigger response actions. The goal is simple: unknown portable media does not touch production systems unless you can prove who owns it, why it is needed, and how it was validated. ¹

Regulatory text

Provided excerpt: “NIST SP 800-53 control AC-19.3.” ²

Operator interpretation of the excerpt: AC-19(3) is an enhancement to AC-19 that focuses specifically on portable storage devices that lack an identifiable owner. In practice, you should implement a rule that unknown/unattributed portable media is not allowed to connect to, mount on, or exchange data with in-scope systems unless you have an approved, logged, and attributable exception. ¹

What an assessor expects to see:

• A clear definition of “portable storage device” and “identifiable owner” for your organization.
• A technical enforcement mechanism (not just guidance) that prevents or constrains use.
• Evidence (logs/tickets/reports) that shows the mechanism is active, monitored, and acted on. ¹

Plain-English interpretation (what AC-19(3) means)

A portable storage device with “no identifiable owner” is any removable storage that you cannot tie to a responsible person or organization through labeling, inventory records, or authoritative assignment. If someone finds a USB drive in a parking lot, receives one at a conference, or pulls an untagged drive from a drawer, it is “no identifiable owner” until your process makes ownership and accountability explicit.

AC-19(3) pushes you toward a default-deny posture for that media class:

• Default: Block or quarantine unknown portable media.
• Controlled alternative: Permit only after ownership is established and the device passes your intake controls (e.g., scanning and authorization).

This control is about accountability and exposure reduction. Your policy language should reflect operational reality: endpoint controls, intake workflow, exception approvals, and incident response hooks. ¹

Who it applies to (entity and operational context)

AC-19(3) typically applies wherever NIST SP 800-53 is your control baseline, including:

• Federal information systems implementing NIST SP 800-53 controls. ¹
• Contractor systems handling federal data where the contract, SSP, or security requirements flow down NIST 800-53 expectations. ¹

Operationally, apply it to:

• End-user endpoints (Windows/macOS/Linux workstations).
• Administrative jump hosts and privileged workstations.
• Servers where removable media access is possible (less common, but high impact).
• Any environment processing sensitive federal data (for example, regulated project enclaves), plus shared services that can become a bridge into those enclaves.

Scope tip: Write down “in-scope system types” and “in-scope user populations” explicitly. Auditors test boundaries, especially for developers, IT admins, and field operations. ¹

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

1) Define “identifiable owner” in enforceable terms

Document criteria that turns “unknown media” into “approved media,” such as:

• Asset tag or physical label with a unique ID.
• Record in an asset inventory that maps the device ID to a custodian.
• Assignment recorded in a ticketing system with manager approval.

Make the definition measurable: if you cannot point to a record, it is “no identifiable owner.” ²

2) Establish a default handling rule: block, then allow by exception

Pick one default model and state it plainly:

• Model A (recommended for most): Block all removable storage unless explicitly authorized.
• Model B: Allow only organization-issued removable media; block everything else.
• Model C (higher operational risk): Allow removable media but block “unknown owner” by device identity and require intake scanning.

Your control statement should match what endpoint tooling can actually enforce. If you cannot reliably identify device identity, do not promise device-identity enforcement. ¹

3) Implement technical enforcement on endpoints

Work with IT/SecOps to implement one or more:

• OS policies restricting removable storage mounting and execution.
• Endpoint protection/EDR rules that detect new removable media and trigger containment actions.
• Device control / endpoint management policies that allow only approved device identifiers.
• DLP policies that prevent copying regulated data to removable media.

Minimum bar for audit readiness: a central policy that pushes to endpoints and produces logs or compliance reports showing devices are blocked or controlled. ¹

4) Create an “intake and validation” workflow for legitimate business needs

You will have edge cases: vendor firmware updates, lab instrumentation, field data collection, incident response imaging. Build a workflow that makes those cases safe:

• Intake request ticket (who, why, system, data sensitivity).
• Approval by system owner and security (and privacy if required by your program).
• Malware scanning and, if feasible, content inspection on a dedicated kiosk or isolated workstation.
• Device labeling and inventory registration.
• Time-bound authorization and return/secure disposal rules.

Avoid informal “just scan it” guidance. Auditors want to see controlled flow and accountability for exceptions. ¹

5) Logging, monitoring, and response

Define what constitutes a violation and what happens next:

• Detection: endpoint event for removable media insertion/mount attempt.
• Action: block/quarantine; alert to SOC or help desk queue.
• Triage: confirm whether device is approved; if not, treat as a security event.
• Remediation: user coaching, disciplinary path if repeated, and root-cause review (policy gap vs. tooling gap).

Tie this to your incident response process so the organization treats unknown media as a real entry vector, not an IT nuisance. ¹

6) Governance: assign ownership and make evidence recurring

Name a control owner (often Endpoint Security or IT Security) and a compliance owner (GRC). Define a cadence to produce artifacts (reports, exception reviews) so you are not scrambling during an assessment. Daydream is often the clean way to manage this mapping: control owner, procedure, and recurring evidence artifacts attached to the requirement so nothing is tribal knowledge. ²

Required evidence and artifacts to retain

Keep evidence that proves both design and operation:

Policy and standards

• Removable media policy with “no identifiable owner” definition and default rule.
• Endpoint configuration standard describing enforcement approach. ¹

Operational procedures

• Intake/exception workflow (ticket fields, approvals, scanning steps, labeling steps).
• User guidance for what to do when unknown media is found. ¹

System evidence

• Endpoint management/device control policy screenshots or exported configs.
• Sample of endpoint logs showing blocked/controlled events.
• Compliance reports showing enforcement coverage across in-scope endpoints.
• Exception tickets showing approvals and closure notes. ¹

Governance evidence

• Control mapping showing control owner, implementation procedure, and evidence list (this is the artifact teams forget). ²
• Periodic exception review notes (what was approved, why, and whether the pattern indicates a needed policy change).

Common exam/audit questions and hangups

Expect these, and prepare crisp answers with artifacts:

• “How do you determine whether a portable storage device has an identifiable owner?”
• “Show me the technical control that blocks unknown devices.”
• “Show exceptions for the last period and the approvals.”
• “How do you ensure developers/admins can’t bypass this?”
• “What happens when a user plugs in an unapproved USB drive? Show the alert and the response record.” ¹

Hangups that derail audits:

• Policy says “prohibited,” but endpoints still mount and read/write freely.
• No evidence of monitoring or response. Auditors treat that as control not operating.
• Exceptions exist, but they are granted by email with no durable record.

Frequent implementation mistakes (and how to avoid them)

1. Relying on user training alone. Training helps, but AC-19(3) is assessed like an access control. Put enforcement in endpoint policy and back it with logs. ¹

2. No shared definition of “owner.” If IT thinks “owner” means the person holding the device and GRC thinks it means asset inventory, your evidence won’t line up. Define it once, publish it, and audit against it.

3. Exception creep. Teams approve “temporary” USB use repeatedly because it’s easier than fixing workflow. Force exceptions to be time-bound and require business justification.

4. Ignoring third-party scenarios. Contractors and other third parties bring media for legitimate work. Your onboarding and site access processes must route them through the same intake controls.

5. No quarantined scanning path. Scanning on the same workstation you are trying to protect defeats the purpose. Build a dedicated kiosk or isolated process and document it.

Enforcement context and risk implications

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

Risk-wise, auditors treat unknown portable media as a predictable ingress path for malware and an easy way to move data off-network. If you cannot show technical restriction plus accountability for exceptions, you will likely face findings framed as control design gaps (policy-only) or operating effectiveness gaps (no logs, no reviews). ¹

A practical execution plan (30/60/90-day)

First 30 days (foundation)

• Confirm scope: in-scope systems, users, environments.
• Publish “identifiable owner” definition and default rule.
• Inventory current endpoint controls and gaps (who can mount USB storage today?).
• Stand up an exception ticket template with required fields and approvals. ¹

Next 60 days (enforcement + workflow)

• Roll out endpoint policy to block unknown/unapproved portable storage for the highest-risk groups first (admins, privileged workstations, sensitive enclaves).
• Build the intake/scanning workflow, including where scans occur and how results are recorded.
• Start capturing recurring evidence: compliance reports, sample event logs, exception register. ¹

By 90 days (audit-ready operations)

• Expand enforcement coverage to remaining in-scope endpoints.
• Run an exception review and document outcomes (patterns, needed policy changes).
• Tabletop the response procedure for an “unknown USB inserted” event and capture the record.
• In Daydream, map AC-19(3) to the control owner, operating procedure, and recurring evidence artifacts so assessment prep is a retrieval task, not a scramble. ²

Frequently Asked Questions

Does AC-19(3) mean we must ban all USB drives?

No. It targets portable storage devices with no identifiable owner. You can permit organization-issued, inventoried, and approved devices, and you can allow exceptions with documented approvals and controls. ¹

What counts as an “identifiable owner” in practice?

Use a definition you can prove: a unique device ID tied to an inventory record and a named custodian, plus a labeling convention that matches the record. If you can’t produce the record during an audit, the device is “no identifiable owner.” ¹

How do we handle third parties who need to bring media onsite?

Route them through the same intake process: request ticket, business justification, security approval, scanning on an approved path, and temporary assignment recorded to a sponsor/custodian. Avoid ad hoc “plug it in and see.” ¹

Is malware scanning alone enough to satisfy AC-19(3)?

Scanning helps, but the requirement’s theme is accountability for devices with no owner. You still need identification/assignment plus technical controls and logs that show unknown devices are blocked or tightly controlled. ¹

What evidence do auditors usually want first?

They start with enforcement proof: endpoint/device-control configuration and logs showing blocks or restrictions, then they trace exceptions to approvals and inventory records. Policy without system evidence rarely passes. ¹

We have developers who argue they need removable media for build/test workflows. What’s the clean approach?

Give them a controlled path: approved, inventoried media; a dedicated scanning station; and an exception workflow for uncommon cases. If the need is frequent, treat it as a standard service with guardrails, not repeated one-off exceptions. ¹

Footnotes

1. NIST SP 800-53 Rev. 5

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