NAS and USB over IP: The Hidden Blind Spots in Endpoint DLP

Data Loss Prevention (DLP) solutions are often viewed as the cornerstone of safeguarding sensitive information, but their effectiveness depends heavily on the scope of what they can monitor. Network attached storage (NAS) and emerging technologies like USB over IP introduce blind spots that traditional endpoint DLP agents struggle to cover. Because these systems operate over network channels rather than local drives or physical ports, they can quietly bypass the rules and restrictions organizations rely on to prevent exfiltration. Understanding how NAS and USB over IP interact with DLP, and why they evade detection, is critical for building a layered defense strategy that closes these gaps before attackers exploit them.

Understanding NAS and Its Relationship with DLP

A NAS device is a network attached storage system that sits on your company’s internal network. While it provides convenience and centralization, it can also become a blind spot for endpoint-based DLP systems.

1. NAS Often Falls Outside DLP Scope

Many DLP agents, like Microsoft Purview Endpoint DLP, are designed to track activity on local drives or synced cloud storage. But when a user copies sensitive files directly from a NAS share to a USB drive, that transfer may bypass detection entirely. Microsoft engineers confirm there’s no native inspection of NAS to USB transfers unless the files first hit a local drive 1.

2. Invisible to Local File Monitoring

Endpoint DLP tools monitor activities on endpoints. They catch file operations like copy, paste, and print on recognized drives. But network shares, including those on NAS, are treated differently. The DLP agent simply does not “see” what’s happening over the network 1.

3. Common DLP Evasion Techniques

Exfiltration via NAS is just one example of a more general category: using trusted storage or protocols that DLP software ignores. Other tactics include encrypted or compressed transfers, or using alternate protocols to hide traffic from scrutiny 2,3.

Diving Into USB Over IP and DLP

USB over IP enables remote USB device connections as if physically plugged in locally. Think remote dongles, scanners, or even flash drives shared over the network.

1. The DLP Agent Doesn’t Recognize It as USB

Since the USB device is accessed over TCP/IP, not a physical port, the DLP endpoint agent treats the traffic as network communication, neither “removable media” nor local or synced storage 1. That means typical USB-blocking rules won’t apply.

2. Encrypted or Proprietary Protocols Mask Traffic

USB over IP often uses proprietary encapsulation protocols and encryption. This makes content invisible to DLP unless the system inspects deep into network traffic, capabilities many endpoint DLP tools don’t possess 2,4.

3. A Fresh Attack Vector

USB over IP opens a new path for data exfiltration. A user could mount a remote USB drive and copy confidential files directly from a NAS, or even a local drive, without tripping USB restrictions, since it’s all happening “over the network.”

Commonalities Between NAS and USB Over IP: Why They Bypass DLP

Shared Characteristic: Treated as Network Traffic

• Both rely on network protocols, not local or removable media paths.

Shared Characteristic: Encrypted or Encapsulated Data

• DLP tools cannot easily examine contents.

Shared Characteristic: Unmonitored Channels

• DLP policies often ignore proprietary or non-traditional data flows.

How to Mitigate These Blind Spots

Enforce Controls Beyond Endpoint DLP

• Use device control policies in tools like Defender for Endpoint or Intune to block USB access entirely, independent of content origin 1.

Monitor Network-Level Transfers

• Deploy network DLP or IDS/NIPS solutions capable of recognizing unusual traffic patterns, including proprietary USB-over-IP protocols or high-volume NAS downloads 2,3.

Harden Your NAS

• Apply access control, content classification, and audit logging on the NAS itself. Solutions like Symantec DLP Data Access Governance can monitor and govern sensitive files on NAS 5.
• Limit share permissions and require sensitivity labels before files can be accessed or downloaded.

Block or Whitelist USB-Over-IP Services

• Use application control to prevent installation or execution of USB-over-IP tools.
• Whitelist approved storage channels and block unofficial or unsanctioned virtual USB services.

Putting It All Together

NAS and USB over IP both represent data exfiltration vectors that can dodge traditional DLP protections. The common thread is that data flows via network channels, bypassing local policy enforcement attached to removable media or local files.

To secure these gaps:

• Monitor and block virtual USB channels.
• Extend DLP to cover network-based transfers.
• Implement strong access governance and classification on NAS systems.
• Employ network level detection for unusual protocols or traffic patterns.

By combining endpoint controls, network visibility, and storage security, you significantly reduce the risk of sensitive data silently slipping out of your organization.

Sources and Further Reading

• Microsoft’s explanation of Endpoint DLP not tracking NAS-to-USB transfers: “Purview endpoint DLP block file from copy directly from NAS to USB” 1
• Overview of DLP evasion techniques including protocol manipulation: Scopd Blog, Soc Investigation 2,3
• Data governance on NAS using Symantec DLP: “Symantec DLP Data Access Governance” 5
• Intro to USB over IP technology: Easy Tech Solver 4

Links

1. Microsoft Q&A: Purview endpoint DLP block file from copy directly from NAS to USB
2. Scopd Blog: How Cybercriminals Bypass DLP Systems
3. Soc Investigation: How to Bypass DLP Policies & General Defense Strategies
4. Symantec: DLP Data Access Governance Datasheet
5. Easy Tech Solver: Unlocking the Magic of USB over IP Would you like me to also create a visual diagram showing NAS and USB-over-IP bypass paths?