Adversaries may move onto systems, such as those separated from the enterprise network, by copying malware to removable media which is inserted into the control systems environment. The adversary may rely on unknowing trusted third parties, such as suppliers or contractors with access privileges, to introduce the removable media. This technique enables initial access to target devices that never connect to untrusted networks, but are physically accessible.
Operators of the German nuclear power plant, Gundremmingen, discovered malware on a facility computer not connected to the internet. [1] [2] The malware included Conficker and W32.Ramnit, which were also found on eighteen removable disk drives in the facility. [3] [4] [5] [6] [7] [8] The plant has since checked for infection and cleaned up more than 1,000 computers. [9] An ESET researcher commented that internet disconnection does not guarantee system safety from infection or payload execution. [10]
| ID | Name | Description |
|---|---|---|
| S0608 | Conficker |
Conficker exploits Windows drive shares. Once it has infected a computer, Conficker automatically copies itself to all visible open drive shares on other computers inside the network. [11] Nuclear power plant officials suspect someone brought in Conficker by accident on a USB thumb drive, either from home or computers found in the power plant's facility. [4] |
| S0603 | Stuxnet |
Stuxnet was able to self-replicate by being spread through removable drives. A willing insider or unknown third party, such as a contractor, may have brought the removable media into the target environment. [12] The earliest version of Stuxnet relied on physical installation, infecting target systems when an infected configuration file carried by a USB stick was opened. [13] |
| ID | Mitigation | Description |
|---|---|---|
| M0942 | Disable or Remove Feature or Program |
Consider the disabling of features such as AutoRun. |
| M0934 | Limit Hardware Installation |
Enforce system policies or physical restrictions to limit hardware such as USB devices on critical assets. |
| M0928 | Operating System Configuration |
Harden the system through operating system controls to prevent the known or unknown use of malicious removable media. |
| ID | Name | Analytic ID | Analytic Description |
|---|---|---|---|
| DET0733 | Detection of Replication Through Removable Media | AN1866 |
Real-time monitoring identifies a Universal Serial Bus (USB) storage device insertion event on an Industrial Control System (ICS) engineering or Human-Machine Interface (HMI) workstation where the device's hardware identifier (ID) is not in the authorized USB allowlist, immediately followed by process execution from the removable drive's path. Documented as the primary infection vector for Stuxnet, which specifically targeted air-gapped Siemens engineering environments via infected USB drives. OT operational-fidelity gate: Alert only when the account/device/session violates the approved identity + source host/jump path/zone policy and is corroborated by access to a protected OT asset, execution, configuration change, or another security-relevant follow-on event. Suppress approved shift activity, vendor support, break-glass use, commissioning, and documented remote-access windows. |
| AN2127 |
Real-time monitoring identifies a mount event for removable storage media on an Industrial Control System (ICS) Linux asset, followed by execution of a binary from the mounted path within a short window. OT operational-fidelity gate: Alert only when the account/device/session violates the approved identity + source host/jump path/zone policy and is corroborated by access to a protected OT asset, execution, configuration change, or another security-relevant follow-on event. Suppress approved shift activity, vendor support, break-glass use, commissioning, and documented remote-access windows. |
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| AN2190 |
Real-time monitoring identifies a new device connecting to an Industrial Control System (ICS) network switch port that was previously unused or previously assigned to a different device Media Access Control (MAC) address immediately following physical access to the environment, with subsequent Industrial Control System (ICS) protocol traffic to field devices. OT operational-fidelity gate: Alert only when the account/device/session violates the approved identity + source host/jump path/zone policy and is corroborated by access to a protected OT asset, execution, configuration change, or another security-relevant follow-on event. Suppress approved shift activity, vendor support, break-glass use, commissioning, and documented remote-access windows. |
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| AN2228 |
Real-time monitoring identifies an Industrial Control System (ICS) protocol file-transfer service such as Distributed Network Protocol 3 (DNP3) File Transfer Object or Internet Electrotechnical Commision (IEC) 61850 file service being used to place files on a field device from a source not in the approved engineering workstation list, outside a scheduled maintenance window, where the transfer source is a device not previously enrolled. OT operational-fidelity gate: Alert only when the account/device/session violates the approved identity + source host/jump path/zone policy and is corroborated by access to a protected OT asset, execution, configuration change, or another security-relevant follow-on event. Suppress approved shift activity, vendor support, break-glass use, commissioning, and documented remote-access windows. |