AC-19(2): Use of Personally Owned Portable Storage Devices

AC-19(2) requires you to control (and typically restrict) the use of personally owned portable storage devices (for example, employee-owned USB drives) with your systems. To operationalize it fast, you need a clear policy decision (ban vs. tightly allow), technical blocks in endpoint tools, an exception workflow, and recurring evidence that the controls work in practice ¹.

Key takeaways:

• Default to “no personally owned portable storage” unless a documented exception is approved and technically constrained ¹.
• Enforcement for this control is usually “audit enforcement”: weak evidence, inconsistent endpoint settings, and uncontrolled exceptions are what fail assessments ².
• Evidence matters as much as design: keep policy, endpoint configuration proof, exception records, and monitoring outputs aligned to AC-19(2) ¹.

Personally owned removable media is a classic “quiet” data loss path because it bypasses many of the controls you built around managed endpoints, approved cloud storage, and enterprise collaboration tools. AC-19(2) exists to force an explicit organizational decision: either prohibit employee-owned portable storage devices, or allow them only under defined, controlled conditions with documentation and oversight ¹.

For a Compliance Officer, CCO, or GRC lead, the operational challenge is rarely philosophical. It’s practical: Which devices count? Where do you block them? Who can grant exceptions? How do you prove, in an assessment, that personally owned removable media is not being used to move controlled information in and out of the environment?

This page gives requirement-level implementation guidance you can execute. It assumes you have a mixed environment (laptops, VDI, privileged admins, third parties, and contractors) and need a defensible stance with audit-ready evidence. It also highlights the most common audit hangups: exceptions that become the norm, endpoint settings that drift, and “policy-only” controls without monitoring artifacts ².

Regulatory text

Framework requirement: “NIST SP 800-53 control AC-19.2.” ¹

Operator meaning (what you must do): AC-19(2) requires you to govern the use of personally owned portable storage devices with organizational systems. In practice, that means you must (1) define whether personal removable media is prohibited or allowed under constraints, (2) implement technical and procedural controls consistent with that decision, and (3) retain evidence that the controls are operating ³.

Plain-English interpretation (for fast alignment)

The ac-19(2): use of personally owned portable storage devices requirement is about preventing uncontrolled data movement via removable media you do not manage. If a device is personally owned, you typically cannot guarantee encryption, malware posture, chain-of-custody, or secure disposal. Auditors expect you to either block it or justify a narrow allowance with guardrails ².

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 this shows up)

• Corporate endpoints (Windows/macOS/Linux), including remote workers.
• Privileged admin workstations and jump hosts.
• Shared workstations in labs, manufacturing, or call centers.
• Third-party/contractor workstations that connect to your environment or handle your data.
• Servers that might accept USB storage (less common, but high risk).

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

1) Make a policy decision you can enforce

Pick one of these two models and document it in your access control / removable media standard:

Model	Default rule	Where it works best	Audit risk
Prohibit	No personally owned portable storage devices may be used with organizational systems.	Most corporate IT environments; regulated data; broad user populations.	Lower, if you can prove technical blocking and exception handling.
Constrained allow	Personal devices allowed only for defined business cases with compensating controls.	Edge cases: field ops, OT constraints, specialized data transfer needs.	Higher, unless constraints are tight and evidenced.

Define “portable storage device” explicitly (USB flash drives, external HDD/SSD, SD cards, mobile device storage in “mass storage” mode). State whether personally owned encrypted drives qualify or still count as personal devices.

2) Implement technical enforcement on endpoints (the control that auditors trust)

Minimum expected technical measures (choose what fits your stack):

• Device control via endpoint management/EDR to block USB mass storage by default.
• Allow-listing for approved corporate-owned encrypted media (by device ID/serial where supported).
• Read-only mode for narrow cases (example: allow reading logs from a camera SD card but block writes).
• Control by user role (developers, admins, help desk) with tighter defaults for privileged users.

What to document:

• The specific setting(s) that block personal removable media.
• The scope (which device groups, OS versions, remote endpoints).
• The exception mechanism (temporary group membership, time-bound policy assignment).

3) Define an exception workflow that does not turn into a loophole

Build a simple intake that the business can follow, and Security can defend:

Exception request minimum fields

• Business justification and data classification involved.
• Device ownership (personal vs. corporate) and make/model/serial (if available).
• Required capability (read, write, both) and target systems.
• Duration and expiration condition.
• Compensating controls (example: corporate-issued encrypted drive instead of personal).

Approval chain

• Data owner (or system owner) approves the business need.
• Security approves the risk and required safeguards.
• IT implements the technical exception.
• GRC records the exception and links it to AC-19(2).

Expiration

• Make exceptions time-bound by design (ticket expires, device removed from allow-list, user removed from exception group).

4) Put monitoring in place (prove it’s working)

Auditors will ask how you know the policy is followed. Build at least one monitoring loop:

• Endpoint telemetry reports: attempted USB mounts blocked, permitted mounts, policy coverage.
• SIEM alerting for mass storage events on sensitive device groups (admins, finance, regulated data handlers).
• Periodic review of allow-lists and exception groups.

If you cannot technically monitor, document an alternative control (for example, restricted physical ports in high-risk areas plus inspection), but expect more scrutiny ².

5) Train the people who will break this first

Focus training on:

• IT support (who gets asked for “just this once”).
• Privileged users.
• Teams working with regulated exports, sensitive customer data, or source code.

Training content should be short: what’s prohibited, how to request an exception, and approved alternatives (corporate encrypted media, managed file transfer, approved cloud sharing).

Required evidence and artifacts to retain

Keep evidence in a control binder (GRC tool or structured repository) mapped to AC-19(2) ¹:

Policy and governance

• Removable media / portable storage standard stating personal device rules.
• Data handling standard showing approved transfer methods.
• Exception procedure and approval matrix.

Technical configuration evidence

• Endpoint management screenshots/exports showing USB mass storage control settings.
• Policy scope reports: % of endpoints in scope is helpful, but avoid unsourced numbers; keep raw system reports instead.
• Allow-list export (approved devices) with timestamps.

Operational evidence

• Sample exception tickets with approvals, implementation notes, and closure/expiration.
• Monitoring outputs (SIEM queries, endpoint event reports) showing blocked attempts and review notes.
• Quarterly (or periodic) review sign-off of exceptions and allow-lists.

Third-party evidence (if applicable)

• Contract language requiring compliance with your removable media restrictions for systems handling your data.
• Attestations or technical enforcement proof for managed contractor endpoints.

Daydream note: many teams fail AC-19(2) because evidence is scattered across ITSM, endpoint tools, and shared drives. Daydream can act as the control system of record by mapping the requirement to a control owner, an implementation procedure, and recurring evidence artifacts so you can produce an assessment-ready packet on demand ¹.

Common exam/audit questions and hangups

Expect these, and prepare the artifacts above:

1. “Show me the policy.” Auditors want explicit language on personally owned portable storage devices, not just “removable media” in general.
2. “Show me enforcement.” A written prohibition without endpoint blocking is a common finding.
3. “How do exceptions work?” If exceptions exist, auditors will test for approvals, scope, and expiration.
4. “How do you know it’s operating?” They will ask for monitoring outputs and evidence of review.
5. “What about contractors?” They will ask whether third parties handling federal data follow the same restrictions ².

Frequent implementation mistakes and how to avoid them

• Mistake: Policy bans personal devices, but IT issues “temporary” exceptions informally.
  Fix: require an ITSM ticket, tie it to a time-bound endpoint policy, and review exceptions periodically.

• Mistake: Blocking only on Windows, ignoring macOS/Linux.
  Fix: define scope by data/system sensitivity, then verify technical coverage across OS populations.

• Mistake: Allow-list includes “unknown” devices.
  Fix: allow-list only corporate-owned encrypted drives or specifically approved device IDs.

• Mistake: No defined alternatives.
  Fix: publish approved transfer methods (managed file transfer, approved cloud storage, corporate encrypted removable media).

• Mistake: Evidence is not reproducible.
  Fix: schedule recurring evidence pulls (exports, screenshots, reports) and store them centrally with timestamps and reviewer sign-off.

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement. Practically, AC-19(2) risk manifests as (1) data exfiltration, (2) malware introduction via removable media, and (3) inability to demonstrate control operation during audits. The most common “enforcement” outcome is assessment findings that trigger POA&Ms, delayed ATOs, or customer trust issues in federal contracting contexts ².

Practical 30/60/90-day execution plan

First 30 days (stabilize and decide)

• Confirm in-scope systems and data types (federal data handling environments first) ².
• Decide policy posture: prohibit vs. constrained allow.
• Draft/update removable media standard and exception procedure.
• Identify your technical control points (endpoint management, EDR, DLP, SIEM) and owners.

Days 31–60 (implement and prove)

• Deploy endpoint controls to block USB mass storage by default on in-scope endpoints.
• Stand up the exception workflow in ITSM with required fields and approvals.
• Create a central evidence folder or GRC control record and start collecting config exports and sample tickets.
• Implement baseline monitoring (USB device events, blocked attempts) and route to Security for review.

Days 61–90 (tighten operations)

• Run an exception and allow-list review; revoke stale entries.
• Add role-based tightening for privileged users and high-risk teams.
• Document third-party expectations and confirm contractor compliance for in-scope work.
• Run a tabletop audit: answer the common audit questions using only retained artifacts; fix gaps.

Frequently Asked Questions

Do we have to ban all USB drives to meet AC-19(2)?

No. You can allow personally owned portable storage devices under defined constraints, but auditors will expect strong technical controls, tight approvals, and evidence of monitoring ².

What counts as “personally owned portable storage” in practice?

Treat any removable storage not issued and managed by your organization as personally owned, including USB flash drives, external drives, and SD cards. Document your definitions in the removable media standard so enforcement and exceptions are consistent.

If we issue corporate encrypted USB drives, does AC-19(2) still matter?

Yes. AC-19(2) is specifically about personally owned devices, but your technical controls should distinguish between corporate-approved media and unapproved personal media. Keep allow-list and encryption requirements documented and evidenced.

How do we handle contractors who need to transfer files into our environment?

Require approved transfer methods (managed file transfer, secure portals) and prohibit personal removable media on systems handling your data. Where contractors use managed endpoints, collect attestations or technical enforcement evidence consistent with your policy ².

What evidence is most persuasive in an audit?

Endpoint configuration exports showing USB mass storage blocked by default, plus a small set of exception tickets showing approvals, technical implementation, and expiration. Add monitoring outputs that demonstrate you detect and review removable media events.

Where does Daydream fit if we already have endpoint tools and ITSM?

Daydream helps you operationalize AC-19(2) as a repeatable control by mapping an owner, a procedure, and the recurring evidence artifacts pulled from endpoint tools and ITSM. That reduces “scramble work” during assessments and keeps exceptions reviewable over time ¹.

Footnotes

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

2. NIST SP 800-53 Rev. 5

3. NIST SP 800-53 Rev. 5; Source: NIST SP 800-53 Rev. 5 OSCAL JSON