I introduced a new feature for this article, since it is quite a bit longer than our usual articles. The information covered here is very important, but maybe you don’t have time to read it right now and you want some quick advice. If this is you:
If you’re in a hurry. Block, disable, hide or never connect anything to the USB port on a CNC machine unless it’s being connected directly to an OT-Max device protecting the CNC.
This article “almost wasn’t”. While working on the original, I had an idea. I wanted to explore whether OT-Max could directly support USB thumb drives, enabling file transfers to a connected CNC machine. So I sent the developer a message inquiring about this possibility. Luckily, having an agile and responsive developer managing that product, the answer, after discussing some details, was yes and it’s going to be implemented in the coming weeks.
So this article almost “wasn’t” because with OT-Max in the loop, you’ll no longer have the degree of danger from USB thumb drives and CNC machines. We will get into more detail on that in the future. In the meantime, if you have CNC machines that support USB thumb drives, this article should help you better understand the unique issues that tiny metal port represents to you.
Thumb Drives and CNC Machines
Why are thumb drives even used? Before we get to that, our own Peter Pickslay had this to say about using USB devices such as thumb drives on CNC machines:
I think the use of USB drives is never acceptable in manufacturing these days and that using a USB drive should not even be a last resort.
He’s not wrong, but the reality is people are using them anyway. So it’s better to be informed if you’re taking the risk, and maybe this article will convince you to implement a “no USB thumb drive” policy, the safest and best approach.
We’ve seen first hand what modern viruses such as a crypto locker can do to a CNC machine, effectively “bricking” them, rendering the system inoperable.
Restoring a bricked CNC is costly, time consuming, and may require extensive assistance from your OEM machine builder. For that reason we’ve also recommended better management of your machine parameters to more gracefully recover from failures of these systems regardless of the cause. Being your communications software provider with CIMCO DNC-Max, we have a perfect way to capture those settings, directly and safely without the need of a USB thumb drive. CNC Machine settings can even be stored in your CIMCO MDM installation.
Some companies still use USB devices to get files to their CNC machines, or for backup purposes. This potentially exposes CNC machines to malware, and the company using them to data breaches, and compliance violations. This is especially concerning for facilities handling controlled materials under frameworks like CMMC 2.0. Below, we explore USB management, the risks involved, and actionable steps to mitigate these threats.
The Unique Risks of CNC Machines
Legacy Operating Systems
Many CNC machines operate on outdated Windows systems, we’ve even seen older controls running Windows 98. An out of date operating system is just not viable to be connected directly to any network, or an insecure usb device. These systems are highly vulnerable to malware and exploits that newer OS versions have mitigated. Unfortunately, upgrading the operating system on CNC machines is often impractical due to hardware dependencies, cost, and downtime. So generally, regardless of age, the operating system on a CNC machine is not hardened for modern threats.
USB-Borne Threats
USB devices remain a vector for malware, capable of introducing worms, ransomware, and even firmware-targeted attacks. Even worse, a compromised CNC can cause the spread of a worm across the facility’s network, affecting other machines. This demonstrates the risk of cascading effects from poor USB management and highlights the importance of proper controls.
HID-based Attacks (BadUSB Exploits)
In addition to conventional malware threats, USB ports on Windows devices are susceptible to HID-based attacks. Windows automatically trusts Human Interface Devices (HIDs) such as keyboards and mice, which makes them a prime target for attackers. Techniques like the BadUSB exploit—sometimes called “Bad Beetle”—allow an attacker to reprogram the firmware of a USB device so that it masquerades as an HID. Once connected, such a device can inject keystrokes or simulate mouse movements to execute commands, install malware, or escalate privileges, all at speeds far beyond human capability. Tools like the USB Rubber Ducky have demonstrated how easily these attacks can bypass traditional security measures because the operating system inherently trusts HIDs.
This firmware-level attack is particularly dangerous since the compromised device appears legitimate to the OS, meaning standard antivirus and security software may not detect its malicious behavior. This risk underscores the importance of rigorous USB controls and, where possible, using a solution like OT-Max to filter and validate USB connections before they reach critical CNC systems.
Compliance and Sensitive Data
Organizations handling Controlled Unclassified Information (CUI) fall under strict regulations, such as CMMC 2.0, NIST 800-171, and often reference additional guidelines like IEC 62443 (for Industrial Automation and Control Systems). These frameworks mandate strong data protection measures. A compromised USB drive that reaches a CNC on a segregated but critical network can threaten compliance and expose sensitive or controlled materials—leading to both financial and reputational damage.
Why Network Isolation and USB Controls Are Critical
Air-Gapping
This article idea stemmed from writing about how to Air Gap with CIMCO Software. Before addressing air-gapping, we must first manage the USB threat effectively. Without doing so would still leave the air-gapped system vulnerable.
For more on Air-Gapping with your CIMCO Software, be sure to subscribe, follow our company socials, or check back often for the upcoming article describing that process in detail and more on why it is important in some situations.
Network Segmentation
Even if air-gapping isn’t feasible, CNC machines should reside on tightly segmented networks. Create separate VLANs or subnets and use firewalls to restrict communication strictly to what is necessary for production functions (e.g., file transfers, machine data collection). “Least privilege” applies equally to devices and people: operators should only have the access required for their tasks, and CNC machines should only communicate with authorized endpoints. If you want a simpler, turnkey approach to isolating and protecting your CNC, consider OT-Max. For manufacturing data, CIMCO MDM is an extremely valuable tool for addressing least privilege for manufacturing data such as CNC files, drawings, etc.
Best Practices for USB Device Management
You should take steps to validate your specific requirements prior to even considering implementing USB thumb drives with CNC machines beyond the hobbyist level. Based on our research, these are some best practices that do reduce and mitigate risk around USB thumb drives:
- Pre-Approved USB Devices: Maintain an inventory of company-issued USB drives. Prohibit personal or unverified devices.
- Encryption and Write Protection: Utilize hardware-encrypted USB drives to secure data in transit. Enable write protection to limit unauthorized changes.
- Pre-Scan USB Drives: Scan all USB devices for malware on an isolated, secure workstation or kiosk before connecting them to CNC machines.
- Disable Autorun Features: Ensure autorun is disabled on all CNCs and related workstations to prevent automatic malware execution.
- Role-Based Access Controls: Limit USB usage to authorized personnel, such as technicians or IT staff. Provide clear guidelines on proper usage and handling.
- Physical Port Security: Consider locking unused USB ports or using port covers to physically prevent unauthorized devices from being inserted.
- Log and Monitor Activity: Use software tools to log USB connections and file transfers. Review these logs regularly to spot anomalies or unauthorized usage.
Kevin suggests dedicating devices to individual machines. He also suggests to disconnect machines from the network if emergency use of USB is required.
A Note on Patch Management and OT Antivirus
Where feasible, regularly apply security updates released by OEMs or operating system vendors. Even partial patches can address critical vulnerabilities. A broad range of specialized OT antivirus and application whitelisting solutions exist for industrial control systems—each with its own features, compatibility considerations, and resource requirements. Organizations should conduct thorough research to determine which solution best fits their legacy environments, regulatory obligations, and operational constraints. While legacy system limitations may complicate patching and whitelisting, even incremental measures can significantly reduce risk.
Training: A Critical Component
A well-informed workforce can be your strongest defense. Training programs should:
- Address USB-related risks, basic malware identification, and safe handling procedures.
- Offer role-specific guidelines for operators, technicians, and IT staff.
- Highlight compliance requirements—such as CMMC 2.0—and the ramifications of non-compliance.
OT-Max: Reducing USB Risks with a Secure Intermediary
In the near future, the CIMCO OT-Max platform will support USB thumb drives for safer file transfers to CNC machines. Instead of directly connecting a USB to the CNC, operators will use OT-Max, which can serve as a secure, monitored, and hardened gateway. By filtering and validating files before they reach the CNC memory, OT-Max drastically reduces the risk of malware being introduced through a simple thumb drive. This approach also simplifies network segmentation since only OT-Max communicates with the machine, cutting down on potential infiltration paths.
Costly Recovery and Why Proactive Security Saves Money
Recovering a bricked CNC can involve more than simply reinstalling the operating system—it may require:
- OEM intervention and re-initiation of machine control software.
- Extended downtime for production, causing lost revenue.
- Potential replacement of specialized hardware components due to obsolescence.
Proactive measures—like locked-down USB usage, network segmentation, and OT-Max integration—are usually far less expensive than a single serious incident. The cascading effects of a malware outbreak not only hurt immediate production but can also compromise reputation and lead to non-compliance challenges.
Recommended Resources for Further Guidance
- CISA (Cybersecurity and Infrastructure Security Agency):
- CISA’s Industrial Control Systems (ICS) Page: Guidance on securing USB devices and industrial systems.
- NIST (National Institute of Standards and Technology):
- ISA/IEC 62443:
- Established standards for securing Industrial Automation and Control Systems, recommended for facilities looking to formalize ICS security.
- Managed Solutions Articles:
- CMMC 2.0 and the Encrypted Shop Floor: How OT-Max Helps You Meet Compliance
- Introducing OT-Max: A Game-Changer for Secure CNC Machine Connectivity
- Let Us Help You Protect Your CIMCO Software Investment
- How to Lock the Reset Button on Moxa Nport Devices
- Making Informed Decisions about Wireless DNC
- How to Isolate your CNC Network by Dual Homing DNC Max
- Vulnerability in SIEMENS Simatic S7-1200
Conclusion
USB devices should not be used without great precaution in any CNC environment. Blocking, disabling or disconnecting USB ports on your CNC machines is the best precaution. When deemed necessary, USB management is essential for any facility relying on USB thumb drives with CNC machines, particularly those handling sensitive or controlled materials. Legacy systems, regulatory obligations, and practical financial considerations all point toward one reality: proactively securing CNC environments is both critical and cost-effective. By blocking the use of USB devices, isolating networks, training staff, and leveraging solutions like OT-Max, organizations can safeguard operations, maintain compliance, and avoid costly disruptions.
[…] reading this article I strongly recommend you review “CNC Machine Security: The Dangers and Management of USB Devices” and “Introducing OT-Max: A Game-Changer for Secure CNC Machine […]