CMMC Level 2 Practice 3.8.8: Prohibit the use of portable storage devices when such devices have no identifiable owner

CMMC Level 2 Practice 3.8.8 requires you to block portable storage devices (for example, USB drives) from connecting to systems that process, store, or transmit CUI unless the device has an identifiable owner tied to a person or managed inventory record. Operationalize it by enforcing technical controls (endpoint/device control) plus an issuance-and-labeling process with logging and exception handling. ¹

Key takeaways:

• Ban “found,” “unlabeled,” and personally-owned removable media on CUI in-scope endpoints unless the owner is identifiable and authorized. ¹
• Pair policy with enforcement: device control, logging, and an inventory/assignment register that proves ownership. ¹
• Assessors will look for both prevention and evidence: configuration, logs, exceptions, and user communications. ²

You will fail 3.8.8 in practice if your organization treats it as a “policy-only” requirement. The intent is simple: removable media with no accountable owner is a high-risk path for malware introduction, data spillage, and loss of Controlled Unclassified Information (CUI). The requirement forces accountability by tying every allowed portable storage device to an identifiable owner and by prohibiting the rest. ¹

For a CCO, GRC lead, or Compliance Officer supporting a CMMC Level 2 program, the fastest path is to define the scope (which endpoints can touch CUI), choose the enforcement method (device control via EDR/MDM/GPO or equivalent), and stand up a lightweight operational process: request, approve, issue, label, log, and revoke. Then build the evidence loop so you can show an assessor what is blocked, what is allowed, who owns it, and how you monitor compliance over time. ²

This page gives requirement-level implementation guidance for the target keyword: cmmc level 2 practice 3.8.8: prohibit the use of portable storage devices when such devices have no identifiable owner requirement.

Regulatory text

Requirement (CMMC Level 2 / NIST SP 800-171 Rev. 2 3.8.8): “Prohibit the use of portable storage devices when such devices have no identifiable owner.” ¹

What the operator must do:

1. Define what counts as “portable storage devices” in your environment (USB mass storage, external SSD/HDD, SD cards, portable encrypted drives, and other removable media).
2. Implement controls so unidentified devices cannot be used on in-scope systems.
3. Maintain a method to identify ownership for allowed devices (assignment to a person or a managed asset record) and prove it with evidence. ¹

CMMC Level 2 assessments evaluate implementation of the NIST SP 800-171 Rev. 2 practices within the CMMC program framework. ^{3 2}

Plain-English interpretation

If someone plugs in a USB drive and you cannot reliably answer “whose device is this and are they authorized,” that device must be blocked from use on CUI in-scope endpoints. “Identifiable owner” means a named individual or a controlled, traceable issuance record (for example, Asset Tag + Assigned User + ticket/approval + custody). A drawer full of generic thumb drives, “conference swag” USBs, or unknown devices found in a parking lot are all prohibited. ¹

Who it applies to

Entities: Defense contractors and other federal contractors that handle CUI and are pursuing or maintaining CMMC Level 2. ³
Operational context: Any environment where CUI is processed, stored, or transmitted (endpoints, engineering workstations, administrative laptops, VDI thin clients with USB passthrough, and systems that can move data to/from CUI repositories). ¹

Scope tip (assessment-relevant): Treat “in-scope” as “can access CUI,” not just “stores CUI.” If a workstation can open CUI from a shared drive, portal, or email, removable media controls apply there too. ²

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

1) Decide your removable media posture (default-deny is easiest to defend)

Create a short decision statement for leadership sign-off:

• Default: Block all USB mass storage on CUI in-scope endpoints.
• Allow: Only organization-issued, encrypted, labeled devices assigned to a named user (or assigned to a controlled role such as “Build Room Media Custodian,” with documented custody).
• Disallow: Personally-owned devices and any device without inventory/assignment metadata. ¹

2) Define “identifiable owner” in a way you can prove

Write a definition you can enforce and audit. Example criteria:

• Device has a unique asset tag/serial recorded in an inventory register.
• Inventory register includes “Assigned to (person),” “Business purpose,” “Approval reference,” and “Return/revocation status.”
• The assigned user is an active workforce member with an approved need. ¹

3) Implement technical enforcement on endpoints

Pick one enforcement path (you can mix by platform, but keep the rule consistent):

Windows (common patterns):

• Device control via EDR (mass storage allowlist by hardware ID/serial).
• Group Policy to block removable storage classes by default; allow by exception group where device control can be enforced.
• Central logging of device connection events.

macOS / Linux / Mobile:

• MDM profiles restricting external media.
• Endpoint agent device control where supported.
• Disable USB storage where feasible in high-risk zones.

Minimum bar: an unknown device should fail closed (blocked) on in-scope endpoints. ¹

4) Stand up the operational process (request → issue → track → revoke)

Build a simple workflow your helpdesk can run:

1. Request: User submits request stating business need, data types involved (CUI?), and duration.
2. Approve: Data owner / security approves based on need-to-know and least privilege.
3. Issue: IT issues an approved device from controlled stock, records serial/asset tag, assigns to user.
4. Label: Physical label with asset tag and “If found, return to…” plus “Org-issued” marking.
5. Register: Update the “Removable Media Register” (system of record can be GRC tool, ticketing system, or CMDB).
6. Configure allowlist: Add device hardware ID/serial to endpoint control allowlist.
7. Train user (micro-instructions): Handling rules, encryption requirement if applicable, reporting lost media, and prohibition on sharing.
8. Return/revoke: On role change/termination or end of need, revoke allowlist entry and recover device. ¹

5) Handle exceptions explicitly (and keep them rare)

Some workflows are real: manufacturing equipment, air-gapped transfers, field operations, or third-party support.

Define an exception record that includes:

• System(s) impacted and justification
• Compensating controls (supervised use, scanning station, time-bound access, dedicated kiosk)
• Approver and expiration
• Evidence of monitoring (logs, check-in/out) ²

6) Monitoring and recurring evidence capture

Assessors will ask, “How do you know the control is still working?”

Operationalize monitoring:

• Review blocked-device events and investigate patterns (repeat offenders, specific locations).
• Spot-check that allowed devices match the register and are still assigned to active users.
• Verify termination/offboarding includes removable media recovery and allowlist removal. ²

A practical way to keep this tight is to map 3.8.8 to a documented control with scheduled evidence capture in your GRC system. Daydream can track the control narrative, owners, test steps, and recurring artifacts so evidence does not get rebuilt during assessment prep. ²

Required evidence and artifacts to retain

Keep artifacts that show design, implementation, and operation:

Policy and process artifacts

• Removable Media Policy (prohibits unknown/unowned portable storage on in-scope systems). ¹
• Definition of “identifiable owner” and “portable storage device” (in policy or standard). ¹
• Exception procedure and approval template. ²

Technical configuration evidence

• Screenshots/exports of device control settings (default block + allowlist rules).
• GPO/MDM profiles that restrict removable storage.
• EDR/MDM reports showing enforcement status across in-scope endpoints.

Operational evidence

• Removable Media Register (asset tag/serial, owner, approval reference, issuance date, return status).
• Tickets/approvals for issued devices and exceptions.
• Logs of USB insertion/blocked events (sampled plus a method to retrieve history).
• Offboarding checklist showing removal/return and allowlist cleanup. ²

Common exam/audit questions and hangups

Use these as your readiness checklist:

1. “Show me that an unknown USB drive is blocked on a CUI workstation.”
   Hangup: Policy exists, but the endpoint accepts the drive.

2. “How do you determine the owner of an allowed device?”
   Hangup: You can name a department, not a person, and there is no custody record.

3. “Do you permit personally-owned USB drives?”
   Hangup: “We discourage it” is not a prohibition.

4. “Where is the inventory/register and who updates it?”
   Hangup: Spreadsheet exists but has no owner, no change control, and is out of date.

5. “How do you handle third-party technicians needing portable media?”
   Hangup: No defined exception path; practice becomes ad hoc. ²

Frequent implementation mistakes (and how to avoid them)

Mistake	Why it fails 3.8.8	Fix
Relying on a written policy only	The device still works; assessors test	Enforce technical blocking on endpoints 1
“Owner” = a shared team or a cabinet	No accountability	Assign to a named individual or formal custodian role with check-in/out records 1
Allowing personal USB drives “if encrypted”	Ownership may be unverifiable and unmanaged	Issue org-owned devices and register them; block the rest 1
Allowlist without lifecycle controls	Drives remain allowed after role change	Tie to HR offboarding and periodic register review 2
Exceptions never expire	Controls erode	Require expiration and renewal evidence 2

Enforcement context and risk implications

CMMC Level 2 is implemented through the DoD’s CMMC program and is tied to eligibility for certain DoD contract work. A weak removable media control is a common pathway for malware introduction and uncontrolled data movement, both of which can threaten CUI handling obligations. Treat 3.8.8 as an operational gate: no owner, no use. ^{3 1}

Practical 30/60/90-day execution plan

First 30 days (stabilize and block the obvious)

• Decide scope: identify in-scope endpoint groups that access CUI. ²
• Publish a short removable media standard: default block; definition of “identifiable owner.” ¹
• Turn on endpoint logging for removable media events; validate you can retrieve logs.

By 60 days (enforce + issue controlled alternatives)

• Deploy device control or equivalent technical blocking across in-scope endpoints.
• Create the Removable Media Register and issuance workflow (ticket template + approval path).
• Procure and issue a small set of organization-controlled devices for approved business cases; allowlist them.

By 90 days (operate like an assessed program)

• Run a tabletop: “unknown USB found” and “user needs to transfer files to lab equipment.”
• Start recurring monitoring reviews; document results and remediations.
• Perform an internal test: attempt to use an unowned device on a sample of in-scope endpoints and retain evidence of the block. ²

If you manage controls in Daydream, store the control narrative, test procedure, and monthly/quarterly evidence pulls in one place so assessors can trace requirement-to-proof without staff heroics. ²

Frequently Asked Questions

Does “identifiable owner” have to be a specific person, or can it be a department?

The safest interpretation is a named individual or a formally defined custodian role with custody records you can show. A generic “IT owns it” label usually fails in practice because it does not prove accountability. ¹

Are personally-owned USB drives allowed if they are encrypted?

3.8.8 is about owner identification and accountability, not only encryption. If you cannot reliably identify and authorize the owner through your process and records, block the device on in-scope endpoints. ¹

What counts as a “portable storage device” for 3.8.8?

Treat removable media that can store data outside the endpoint as in scope: USB mass storage, external drives, SD cards, and similar devices. Document your definition and enforce it consistently. ¹

How do we handle USB drives required for manufacturing or lab equipment?

Use a time-bound exception with a documented business need and compensating controls like a dedicated transfer station, supervised handling, and check-in/out custody. Keep the exception record and related logs for assessment evidence. ²

What evidence is most persuasive to an assessor?

A live demonstration (unknown drive is blocked), exported configuration showing default-deny plus allowlist, and a register that maps each allowed device to an owner with approvals. Pair that with log samples and exception records. ²

If we already block USB storage everywhere, do we still need a register?

If the block is absolute and you have no exceptions, the register may be minimal. If any portable storage is permitted, you need an ownership method you can prove, and a register is the simplest way to do that. ¹

Footnotes

1. NIST SP 800-171 Rev. 2

2. DoD CMMC Program Guidance

3. 32 CFR Part 170