SI-3(5): Portable Storage Devices

SI-3(5): Portable Storage Devices requires you to control and scan portable storage media so it cannot introduce malware into your environment. Operationally, you need a documented, enforced workflow for approving portable media, scanning it before use (and ideally on insertion), and retaining evidence that the control runs consistently across endpoints. ¹

Key takeaways:

• Treat all portable storage as a malware ingress path and put it behind a controlled, logged process. ¹
• Standardize technical enforcement (device control + anti-malware scanning) and pair it with a simple user procedure. ²
• Keep evidence that proves coverage (configuration, logs, exceptions, and review records), not just a policy PDF. ¹

Portable storage devices are one of the fastest ways to bypass your network controls. A USB drive can arrive from a third party, a conference, a field site, or a developer’s desk drawer, then touch a high-trust endpoint in seconds. SI-3(5) exists to prevent that “air gap” in your defenses by requiring protective measures focused specifically on portable storage media within the broader anti-malware program. ²

For a Compliance Officer, CCO, or GRC lead, the practical challenge is rarely deciding that USB drives are risky. The challenge is making the requirement executable: defining what counts as portable storage, deciding what is allowed, turning those decisions into endpoint controls, and producing assessor-ready evidence that the controls are operating. SI-3(5) becomes straightforward when you treat it as an operational pipeline: request/approval, technical enforcement, scanning, logging, exception handling, and periodic review. ¹

This page gives requirement-level implementation guidance for the target keyword, si-3(5): portable storage devices requirement, with a step-by-step build plan, evidence checklist, and audit questions you can pre-answer.

Regulatory text

Provided excerpt: “NIST SP 800-53 control SI-3.5.” ¹

What the operator must do (practical interpretation): SI-3(5) is an enhancement under SI-3 (Malicious Code Protection) focused on portable storage devices. You must implement controls that prevent portable storage media from becoming a delivery mechanism for malicious code. In practice, assessors expect (1) defined rules for portable media, (2) technical enforcement on endpoints, and (3) auditable records that show portable media is scanned/controlled as designed. ³

Plain-English interpretation (what SI-3(5) is asking for)

You need to ensure that portable storage devices cannot introduce malware into organizational systems. That usually means:

• You restrict which portable storage can be used (or block it by default).
• You automatically scan portable media for malicious content before files execute or transfer.
• You log usage and handle exceptions with explicit approval and compensating controls. ²

Think of SI-3(5) as “endpoint malware control, specifically for removable media,” not as a general awareness or policy requirement. Policies help, but technical enforcement and evidence carry the audit. ¹

Who it applies to

Entity scope

• Federal information systems and contractor systems handling federal data. ¹

Operational scope (where you must implement)

• End-user endpoints (Windows/macOS/Linux) where removable media can be connected.
• Servers or specialized workstations that ingest data from removable media (engineering stations, lab devices, manufacturing/OT jump hosts).
• Any managed environment where staff transfer files via removable media due to field constraints or segmented networks. ²

Third-party risk angle Portable storage frequently enters through third parties (integrators, field technicians, consultants). Your SI-3(5) procedure should explicitly cover third-party personnel accessing your endpoints or providing media for data transfer, because the control is only as strong as the weakest “bring your own USB” moment. ²

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

Use this as an implementation runbook you can hand to IT/SecOps and track in your GRC system.

1) Define “portable storage device” for your environment

Create a short scoping statement that names what is in-scope:

• USB flash drives, USB external hard drives/SSDs
• SD/microSD cards
• USB-connected smartphones when used as mass storage
• Optical media if your environment still supports it (CD/DVD) ²

Also define what is out-of-scope and why (example: “USB keyboards/mice are not storage and are covered under device control elsewhere”). Keep this tight.

2) Set a default rule: block, allow-list, or controlled use

Pick one enforceable stance:

• Block by default and allow only approved/encrypted corporate media.
• Allow with mandatory scanning and logging, with restrictions for high-trust systems.
• Segmented policy: stricter controls for privileged/admin workstations and sensitive enclaves; more permissive for standard endpoints.

Document your decision and map it to system impact level and mission needs. Assessors will ask why your rule is appropriate. ²

3) Implement endpoint technical controls

Your technical stack can vary, but your outcomes must be consistent:

A. Device control

• Enforce removable storage policy via endpoint management (e.g., MDM/UEM/GPO equivalents).
• Disable auto-run/auto-mount behaviors where applicable.
• Require approved device IDs or certificates if your tooling supports it.

B. Anti-malware scanning for removable media

• Configure your anti-malware/EDR to scan removable media on access or insertion.
• Block execution of suspicious files from removable media based on your detection policy.
• Ensure scanning updates and signatures apply to endpoints that may be offline for periods (field laptops). ²

C. Logging and alerting

• Log removable media insertion events where your endpoint stack supports it.
• Log malware detections tied to removable media source.
• Route relevant logs to your SIEM or central logging for retention and review. ²

4) Build a simple user workflow (so people can comply)

Controls fail when people need an exception and the only path is “ignore the rule.”

Minimum workflow:

1. User requests portable media use (ticket).
2. Manager/system owner approves business need.
3. Security approves based on destination system sensitivity.
4. If approved, user must scan media on a designated “kiosk” endpoint or through enforced endpoint scanning.
5. Transfer occurs.
6. Ticket captures what media was used, what system was accessed, and confirmation of scan outcome.

Keep it lightweight. Your goal is to prevent shadow processes. ¹

5) Handle exceptions and compensating controls

Document when you allow an exception (examples: emergency patching in a disconnected environment, vendor-provided firmware media).

For each exception, record:

• Scope (users/systems/time period)
• Compensating controls (dedicated scanning station, quarantined transfer host, increased monitoring)
• Approval and expiration
• Post-use review (did anything trigger detections?) ²

6) Operationalize governance: assign an owner and recurring evidence

Make the control assessable:

• Assign a control owner (typically Endpoint Security or SecOps).
• Define recurring checks: configuration drift review, sample log review, exception review.
• Put the cadence into your compliance calendar.

Daydream fits well here as the system of record that ties SI-3(5) to an owner, a procedure, and the evidence artifacts you collect on a recurring basis, so audits don’t turn into a scramble for screenshots. ¹

Required evidence and artifacts to retain

Aim for evidence that proves design and operation.

Design artifacts

• Portable storage standard (what’s allowed, where, and under what conditions)
• Endpoint configuration baselines (device control + anti-malware removable media settings)
• Exception procedure and approval matrix (RACI)

Operating evidence

• Endpoint policy export or screenshots showing removable media restrictions and scanning settings
• Centralized reports showing endpoints are receiving the policy (coverage evidence)
• Sample logs of removable media events and corresponding scan/detection logs
• Ticket records for approved portable media use and exceptions
• Periodic review notes (what you checked, what you found, what you fixed) ²

Evidence hygiene tip Store artifacts by system boundary and time period. Auditors often accept sampling, but only if you can explain how the sample represents the population.

Common exam/audit questions and hangups

Expect these lines of questioning:

1. “Show me how portable media is controlled on endpoints.” They want to see enforced settings, not guidance. ²
2. “How do you ensure scanning happens before files are used?” Be ready to show EDR/AV configuration and logs tied to removable media.
3. “What about admins, developers, and IT staff?” Privileged users often bypass controls unless you explicitly cover privileged endpoints.
4. “How do third parties interact with your policy?” If contractors plug media into your devices, your control must still hold. ²
5. “Show your exception register.” Missing or stale exceptions is a common finding.

Frequent implementation mistakes (and how to avoid them)

• Mistake: Policy-only compliance. Avoid relying on an acceptable use policy without technical enforcement. Keep configuration exports and enforcement reports. ¹
• Mistake: Scanning exists, but removable media scanning is not enabled. Many tools support it but leave it off or inconsistent across device groups. Validate on representative endpoints.
• Mistake: No coverage story. If you cannot prove most endpoints are managed and receiving policy, the assessor will treat controls as partial.
• Mistake: Exceptions become permanent. Put expirations on exceptions and run periodic reviews.
• Mistake: Ignoring “non-standard” endpoints. Kiosks, jump boxes, lab systems, and OT-adjacent machines often have USB enabled “temporarily.” Track them explicitly.

Enforcement context and risk implications

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

Risk-wise, removable media is a high-trust ingestion path: it can bypass email filtering, web gateways, and some network monitoring. A weak SI-3(5) implementation increases the likelihood of malware introduction, lateral movement from a single endpoint, and incident scope expansion into sensitive enclaves. ²

Practical 30/60/90-day execution plan

First 30 days (stabilize and scope)

• Confirm scope: endpoints, enclaves, user populations, third-party access scenarios.
• Document your portable media rule (block/allow-list/controlled use) and exception process.
• Identify technical owners for endpoint management and EDR/AV configuration.
• Pull current-state evidence: current removable media settings, current anti-malware config, and any existing tickets/exceptions. ²

Days 31–60 (implement and prove operation)

• Roll out device control policy to a pilot group, then expand.
• Turn on removable media scanning and confirm it works with test media and benign test files.
• Enable logging for insertion events and detections; route to centralized logging.
• Stand up the approval workflow and exception register in your ticketing/GRC process (Daydream or your existing system). ¹

Days 61–90 (harden, measure, and prepare for assessment)

• Expand controls to privileged endpoints and high-sensitivity systems first.
• Run a review cycle: sample endpoints for policy compliance, review logs, close configuration gaps.
• Validate third-party procedures (contractor access, field service scenarios).
• Package your evidence: policy/standard, configs, logs, exceptions, and review record for the assessment period. ²

Frequently Asked Questions

Do we have to ban all USB drives to meet the si-3(5): portable storage devices requirement?

No. SI-3(5) drives control and malware protection outcomes, so you can allow portable media if you enforce scanning, restrictions, and auditable logging. Your rule should match system sensitivity and be consistently enforced. ²

What evidence is strongest for auditors: policy, screenshots, or logs?

Logs and configuration exports tend to carry the most weight because they show operation, not intent. Keep the policy/standard too, but pair it with proof that endpoints received and enforced the settings. ²

How do we handle contractors who bring their own portable media?

Treat third-party media as untrusted by default. Require approval and scanning via a controlled path (for example, a designated scanning station) before it touches production endpoints, and record the exception/approval. ²

Does SI-3(5) apply to cloud-only organizations with no corporate laptops?

If users do not have endpoints that accept portable storage in your system boundary, your scope may be limited. Document the rationale and confirm you are not overlooking managed devices used for administration or support. ¹

What if our EDR product can’t log USB insertion events?

You can still meet the intent by enforcing scanning and restricting device use through endpoint management, then collecting alternative logs available to you. Document the limitation and your compensating evidence path. ²

How should we structure exceptions so they don’t become audit findings?

Use time-bound approvals, define compensating controls, and maintain an exception register with periodic review. Auditors commonly flag exceptions that have no owner, no expiration, or no evidence of review. ²

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