MITRE ATT&CK® techniques for Embedded

Adversaries may activate firmware update mode on devices to prevent expected response functions from engaging in reaction to an emergency or process malfunction. For example, devices such as protection relays may have an operation mode designed for firmware installation. This mode may halt process monitoring and related functions to allow new firmware to be loaded. A device left in update mode may be placed in an inactive holding state if no firmware is provided to it. By entering and leaving a device in this mode, the adversary may deny its usual functionalities.

Adversaries with privileged network access may seek to modify network traffic in real time using adversary-in-the-middle (AiTM) attacks. [1] This type of attack allows the adversary to intercept traffic to and/or from a particular device on the network. If a AiTM attack is established, then the adversary has the ability to block, log, modify, or inject traffic into the communication stream. There are several ways to accomplish this attack, but some of the most-common are Address Resolution Protocol (ARP) poisoning and the use of a proxy. [2]

An AiTM attack may allow an adversary to perform the following attacks: Block Reporting Message, Spoof Reporting Message, Modify Parameter, Unauthorized Command Message

Adversaries may target protection function alarms to prevent them from notifying operators of critical conditions. Alarm messages may be a part of an overall reporting system and of particular interest for adversaries. Disruption of the alarm system does not imply the disruption of the reporting system as a whole.

A Secura presentation on targeting OT notes a dual fold goal for adversaries attempting alarm suppression: prevent outgoing alarms from being raised and prevent incoming alarms from being responded to. [1] The method of suppression may greatly depend on the type of alarm in question:

* An alarm raised by a protocol message * An alarm signaled with I/O * An alarm bit set in a flag (and read)

In ICS environments, the adversary may have to suppress or contend with multiple alarms and/or alarm propagation to achieve a specific goal to evade detection or prevent intended responses from occurring. [1] Methods of suppression may involve tampering or altering device displays and logs, modifying in memory code to fixed values, or even tampering with assembly level instruction code.

Adversaries may automate collection of industrial environment information using tools or scripts. This automated collection may leverage native control protocols and tools available in the control systems environment. For example, the OPC protocol may be used to enumerate and gather information. Access to a system or interface with these native protocols may allow collection and enumeration of other attached, communicating servers and devices.

Adversaries may leverage AutoRun functionality or scripts to execute malicious code. Devices configured to enable AutoRun functionality or legacy operating systems may be susceptible to abuse of these features to run malicious code stored on various forms of removeable media (i.e., USB, Disk Images [.ISO]). Commonly, AutoRun or AutoPlay are disabled in many operating systems configurations to mitigate against this technique. If a device is configured to enable AutoRun or AutoPlay, adversaries may execute code on the device by mounting the removable media to the device, either through physical or virtual means. This may be especially relevant for virtual machine environments where disk images may be dynamically mapped to a guest system on a hypervisor.

An example could include an adversary gaining access to a hypervisor through the management interface to modify a virtual machine’s hardware configuration. They could then deploy an iso image with a malicious AutoRun script to cause the virtual machine to automatically execute the code contained on the disk image. This would enable the execution of malicious code within a virtual machine without needing any prior remote access to that system.

Operational technology communications occur over serial COM, Ethernet, Wi-Fi, cellular (4G/5G), and satellite mediums. Adversaries may block communications to prevent reporting messages and command messages from reaching their intended target devices disrupting processes, operations, and causing cyber-physical impacts.[1]

Adversaries may block communications by either making modifications to software (System Firmware, Module Firmware, Hooking, and Rootkit) and services (Service Stop, Denial of Service) on systems and devices or by positioning themselves between systems and devices and intercepting and blocking the communications such as the case with an Adversary-in-the-Middle attack.

Adversaries may block messages between systems and devices in an OT/ICS environment to disrupt processes. Messages typically fall into two categories: (1) reporting messages that contain telemetry data about the current state of systems, devices, and processes and (2) command messages that contain instructions to control systems, devices, and processes. Both types of messages are critical for the proper functioning of industrial control processes and failure of the messages to reach their intended destinations could inhibit response functions or create an unsafe condition that could have physical impacts.[1][2]

Adversaries may block communications by either making modifications to software (System Firmware, Module Firmware, Hooking, and Rootkit) and services (Service Stop, Denial of Service) on systems and devices or by positioning themselves between systems and devices and intercepting and blocking the communications such as the case with an Adversary-in-the-Middle attack.

Adversaries may perform broadcast discovery requests to enumerate systems and devices on a network. Broadcast discovery works by one system or device sending messages to all systems and devices on a network (or subnet) and then waiting for a response. If a response is received that means the system or device that responded is live and can communicate over that protocol. Adversaries may leverage different protocols supported on the network for sending broadcast messages.

Some common OT protocols that have broadcast discovery mechanisms are Building Automation and Control Network (BACNet) Who-Is requests, Common Industrial Protocol (CIP) List Identity User Datagram Protocol (UDP) broadcast requests, and Siemens S7 broadcast identification requests.[1][2]

Adversaries may repetitively or successively change I/O point values to perform an action. Brute Force I/O may be achieved by changing either a range of I/O point values or a single point value repeatedly to manipulate a process function. The adversary's goal and the information they have about the target environment will influence which of the options they choose. In the case of brute forcing a range of point values, the adversary may be able to achieve an impact without targeting a specific point. In the case where a single point is targeted, the adversary may be able to generate instability on the process function associated with that particular point.

Adversaries may use Brute Force I/O to cause failures within various industrial processes. These failures could be the result of wear on equipment or damage to downstream equipment.

Adversaries may modify software and device credentials to prevent operator and responder access. Depending on the device, the modification or addition of this password could prevent any device configuration actions from being accomplished and may require a factory reset or replacement of hardware. These credentials are often built-in features provided by the device vendors as a means to restrict access to management interfaces.

An adversary with access to valid or hardcoded credentials could change the credential to prevent future authorized device access. Change Credential may be especially damaging when paired with other techniques such as Modify Program, Data Destruction, or Modify Controller Tasking. In these cases, a device’s configuration may be destroyed or include malicious actions for the process environment, which cannot not be removed through normal device configuration actions.

Additionally, recovery of the device and original configuration may be difficult depending on the features provided by the device. In some cases, these passwords cannot be removed onsite and may require that the device be sent back to the vendor for additional recovery steps.

A chain of incidents occurred in Germany, where adversaries locked operators out of their building automation system (BAS) controllers by enabling a previously unset BCU key. [1]

Adversaries may change the operating mode of a controller to gain additional access to engineering functions such as Program Download. Programmable controllers typically have several modes of operation that control the state of the user program and control access to the controllers API. Operating modes can be physically selected using a key switch on the face of the controller but may also be selected with calls to the controllers API. Operating modes and the mechanisms by which they are selected often vary by vendor and product line. Some commonly implemented operating modes are described below:

* Program - This mode must be enabled before changes can be made to a devices program. This allows program uploads and downloads between the device and an engineering workstation. Often the PLCs logic Is halted, and all outputs may be forced off. [1] * Run - Execution of the devices program occurs in this mode. Input and output (values, points, tags, elements, etc.) are monitored and used according to the programs logic. Program Upload and Program Download are disabled while in this mode. [2] [3] [1] [4] * Remote - Allows for remote changes to a PLCs operation mode. [4] * Stop - The PLC and program is stopped, while in this mode, outputs are forced off. [3] * Reset - Conditions on the PLC are reset to their original states. Warm resets may retain some memory while cold resets will reset all I/O and data registers. [3] * Test / Monitor mode - Similar to run mode, I/O is processed, although this mode allows for monitoring, force set, resets, and more generally tuning or debugging of the system. Often monitor mode may be used as a trial for initialization. [2]

Adversaries may block a command message from reaching its intended target to prevent command execution. In OT networks, command messages are sent to provide instructions to control system devices. A blocked command message can inhibit response functions from correcting a disruption or unsafe condition.[1][2]

Adversaries may send unauthorized command messages to instruct control system assets to perform actions outside of their intended functionality, or without the logical preconditions to trigger their expected function. Command messages are used in ICS networks to give direct instructions to control systems devices. If an adversary can send an unauthorized command message to a control system, then it can instruct the control systems device to perform an action outside the normal bounds of the device's actions. An adversary could potentially instruct a control systems device to perform an action that will cause an Impact.[1]. An adversary could also misuse control system devices to store data collected from the network for later use.

In the Dallas Siren incident, adversaries were able to send command messages to activate tornado alarm systems across the city without an impending tornado or other disaster.[2][3]

Adversaries may communicate over a commonly used port to bypass firewalls or network detection systems and to blend in with normal network activity, to avoid more detailed inspection. They may use the protocol associated with the port, or a completely different protocol. They may use commonly open ports, such as the examples provided below. * TCP:80 (HTTP) * TCP:443 (HTTPS) * TCP/UDP:53 (DNS) * TCP:1024-4999 (OPC on XP/Win2k3) * TCP:49152-65535 (OPC on Vista and later) * TCP:23 (TELNET) * UDP:161 (SNMP) * TCP:502 (MODBUS) * TCP:102 (S7comm/ISO-TSAP) * TCP:20000 (DNP3) * TCP:44818 (Ethernet/IP)

Adversaries may use a connection proxy to direct network traffic between systems or act as an intermediary for network communications.

The definition of a proxy can also be expanded to encompass trust relationships between networks in peer-to-peer, mesh, or trusted connections between networks consisting of hosts or systems that regularly communicate with each other.

The network may be within a single organization or across multiple organizations with trust relationships. Adversaries could use these types of relationships to manage command and control communications, to reduce the number of simultaneous outbound network connections, to provide resiliency in the face of connection loss, or to ride over existing trusted communications paths between victims to avoid suspicion. CitationEnterprise ATT&CK January 2018

Adversaries may perform data destruction over the course of an operation. The adversary may drop or create malware, tools, or other non-native files on a target system to accomplish this, potentially leaving behind traces of malicious activities. Such non-native files and other data may be removed over the course of an intrusion to maintain a small footprint or as a standard part of the post-intrusion cleanup process. CitationEnterprise ATT&CK January 2018

Data destruction may also be used to render operator interfaces unable to respond and to disrupt response functions from occurring as expected. An adversary may also destroy data backups that are vital to recovery after an incident.

Standard file deletion commands are available on most operating system and device interfaces to perform cleanup, but adversaries may use other tools as well. Two examples are Windows Sysinternals SDelete and Active@ Killdisk.

Adversaries may target and collect data from information repositories. This can include sensitive data such as specifications, schematics, or diagrams of control system layouts, devices, and processes. Examples of information repositories include reference databases in the process environment, as well as databases in the corporate network that might contain information about the ICS.CitationCybersecurity & Infrastructure Security Agency March 2018

Information collected from these systems may provide the adversary with a better understanding of the operational environment, vendors used, processes, or procedures of the ICS.

In a campaign between 2011 and 2013 against ONG organizations, Chinese state-sponsored actors searched document repositories for specific information such as, system manuals, remote terminal unit (RTU) sites, personnel lists, documents that included the string SCAD*, user credentials, and remote dial-up access information. [2]

Adversaries may target and collect data from local system sources, such as file systems, configuration files, or local databases. This can include sensitive data such as specifications, schematics, or diagrams of control system layouts, devices, and processes.

Adversaries may do this using Command-Line Interface or Scripting techniques to interact with the file system to gather information. Adversaries may also use Automated Collection on the local system.

Adversaries may leverage manufacturer or supplier set default credentials on control system devices. These default credentials may have administrative permissions and may be necessary for initial configuration of the device. It is general best practice to change the passwords for these accounts as soon as possible, but some manufacturers may have devices that have passwords or usernames that cannot be changed.[1]

Default credentials are normally documented in an instruction manual that is either packaged with the device, published online through official means, or published online through unofficial means. Adversaries may leverage default credentials that have not been properly modified or disabled.

Adversaries may perform Denial-of-Service (DoS) attacks to disrupt expected device functionality. Examples of DoS attacks include overwhelming the target device with a high volume of requests in a short time period and sending the target device a request it does not know how to handle. Disrupting device state may temporarily render it unresponsive, possibly lasting until a reboot can occur. When placed in this state, devices may be unable to send and receive requests, and may not perform expected response functions in reaction to other events in the environment.

Some ICS devices are particularly sensitive to DoS events, and may become unresponsive in reaction to even a simple ping sweep. Adversaries may also attempt to execute a Permanent Denial-of-Service (PDoS) against certain devices, such as in the case of the BrickerBot malware. [1]

Adversaries may exploit a software vulnerability to cause a denial of service by taking advantage of a programming error in a program, service, or within the operating system software or kernel itself to execute adversary-controlled code. Vulnerabilities may exist in software that can be used to cause a denial of service condition.

Adversaries may have prior knowledge about industrial protocols or control devices used in the environment through Remote System Information Discovery. There are examples of adversaries remotely causing a Device Restart/Shutdown by exploiting a vulnerability that induces uncontrolled resource consumption. [2] [3] [4]

Adversaries may gather information about a PLCs or controllers current operating mode. Operating modes dictate what change or maintenance functions can be manipulated and are often controlled by a key switch on the PLC (e.g., run, prog [program], and remote). Knowledge of these states may be valuable to an adversary to determine if they are able to reprogram the PLC. Operating modes and the mechanisms by which they are selected often vary by vendor and product line. Some commonly implemented operating modes are described below:

* Program - This mode must be enabled before changes can be made to a devices program. This allows program uploads and downloads between the device and an engineering workstation. Often the PLCs logic Is halted, and all outputs may be forced off. [1] * Run - Execution of the devices program occurs in this mode. Input and output (values, points, tags, elements, etc.) are monitored and used according to the programs logic.Program Upload and Program Download are disabled while in this mode. [2] [3] [1] [4] * Remote - Allows for remote changes to a PLCs operation mode. [4] * Stop - The PLC and program is stopped, while in this mode, outputs are forced off. [3] * Reset - Conditions on the PLC are reset to their original states. Warm resets may retain some memory while cold resets will reset all I/O and data registers. [3] * Test / Monitor mode - Similar to run mode, I/O is processed, although this mode allows for monitoring, force set, resets, and more generally tuning or debugging of the system. Often monitor mode may be used as a trial for initialization. [2]

Adversaries may forcibly restart or shutdown a device in an ICS environment to disrupt and potentially negatively impact physical processes. Methods of device restart and shutdown exist in some devices as built-in, standard functionalities. These functionalities can be executed using interactive device web interfaces, CLIs, and network protocol commands.

Unexpected restart or shutdown of control system devices may prevent expected response functions happening during critical states.

A device restart can also be a sign of malicious device modifications, as many updates require a shutdown in order to take effect.

Adversaries may execute a full program download to a PLC to overwrite the entire PLC program and configuration to deploy a new project or make major changes. This typically requires stopping the PLC and adversely impacting control processes.

The ability to perform a full program download to the PLC typically relies on access to a workstation with the vendor-specific PLC programming software installed.

Adversaries may block access to Ethernet communications to prevent instructions or configurations messages from reaching target systems and devices. Ethernet connections allow for communications between IT and OT systems and devices. Blocking Ethernet communications may also block command and reporting messages.[1]

An adversary may block Ethernet communications by disabling network interfaces, Service Stop, or conducting an Adversary-in-the-Middle attack and dropping the network traffic.

Adversaries may attempt to leverage Application Program Interfaces (APIs) used for communication between control software and the hardware. Specific functionality is often coded into APIs which can be called by software to engage specific functions on a device or other software.

Adversaries may leverage weaknesses to exploit internet-facing software for initial access into an industrial network. Internet-facing software may be user applications, underlying networking implementations, an assets operating system, weak defenses, etc. Targets of this technique may be intentionally exposed for the purpose of remote management and visibility.

An adversary may seek to target public-facing applications as they may provide direct access into an ICS environment or the ability to move into the ICS network. Publicly exposed applications may be found through online tools that scan the internet for open ports and services. Version numbers for the exposed application may provide adversaries an ability to target specific known vulnerabilities. Exposed control protocol or remote access ports found in Commonly Used Port may be of interest by adversaries.

Adversaries may exploit a software vulnerability to take advantage of a programming error in a program, service, or within the operating system software or kernel itself to evade detection. Vulnerabilities may exist in software that can be used to disable or circumvent security features.

Adversaries may have prior knowledge through Remote System Information Discovery about security features implemented on control devices. These device security features will likely be targeted directly for exploitation. There are examples of firmware RAM/ROM consistency checks on control devices being targeted by adversaries to enable the installation of malicious System Firmware.

Adversaries may exploit software vulnerabilities in an attempt to elevate privileges. Exploitation of a software vulnerability occurs when an adversary takes advantage of a programming error in a program, service, or within the operating system software or kernel itself to execute adversary-controlled code. Security constructs such as permission levels will often hinder access to information and use of certain techniques, so adversaries will likely need to perform privilege escalation to include use of software exploitation to circumvent those restrictions. [1]

When initially gaining access to a system, an adversary may be operating within a lower privileged process which will prevent them from accessing certain resources on the system. Vulnerabilities may exist, usually in operating system components and software commonly running at higher permissions, that can be exploited to gain higher levels of access on the system. This could enable someone to move from unprivileged or user level permissions to SYSTEM or root permissions depending on the component that is vulnerable. This may be a necessary step for an adversary compromising an endpoint system that has been properly configured and limits other privilege escalation methods. [1]

Adversaries may exploit a software vulnerability to take advantage of a programming error in a program, service, or within the operating system software or kernel itself to enable remote service abuse. A common goal for post-compromise exploitation of remote services is for initial access into and lateral movement throughout the ICS environment to enable access to targeted systems. CitationEnterprise ATT&CK

ICS asset owners and operators have been affected by ransomware (or disruptive malware masquerading as ransomware) migrating from enterprise IT to ICS environments: WannaCry, NotPetya, and BadRabbit. In each of these cases, self-propagating (wormable) malware initially infected IT networks, but through exploit (particularly the SMBv1-targeting MS17-010 vulnerability) spread to industrial networks, producing significant impacts. [2]

Adversaries may leverage external remote services as a point of initial access into your network. These services allow users to connect to internal network resources from external locations. Examples are VPNs, Citrix, and other access mechanisms. Remote service gateways often manage connections and credential authentication for these services. [1]

External remote services allow administration of a control system from outside the system. Often, vendors and internal engineering groups have access to external remote services to control system networks via the corporate network. In some cases, this access is enabled directly from the internet. While remote access enables ease of maintenance when a control system is in a remote area, compromise of remote access solutions is a liability. The adversary may use these services to gain access to and execute attacks against a control system network. Access to valid accounts is often a requirement.

As they look for an entry point into the control system network, adversaries may begin searching for existing point-to-point VPN implementations at trusted third party networks or through remote support employee connections where split tunneling is enabled. [2]

Adversaries may attempt to gain access to a machine via a Graphical User Interface (GUI) to enhance execution capabilities. Access to a GUI allows a user to interact with a computer in a more visual manner than a CLI. A GUI allows users to move a cursor and click on interface objects, with a mouse and keyboard as the main input devices, as opposed to just using the keyboard.

If physical access is not an option, then access might be possible via protocols such as VNC on Linux-based and Unix-based operating systems, and RDP on Windows operating systems. An adversary can use this access to execute programs and applications on the target machine.

Adversaries may leverage credentials that are hardcoded in software or firmware to gain an unauthorized interactive user session to an asset. Examples credentials that may be hardcoded in an asset include:

* Username/Passwords * Cryptographic keys/Certificates * API tokens

Unlike Default Credentials, these credentials are built into the system in a way that they either cannot be changed by the asset owner, or may be infeasible to change because of the impact it would cause to the control system operation. These credentials may be reused across whole product lines or device models and are often not published or known to the owner and operators of the asset.[1][2]

Adversaries may utilize these hardcoded credentials to move throughout the control system environment or provide reliable access for their tools to interact with industrial assets.

Adversaries may hook into application programming interface (API) functions used by processes to redirect calls for execution and privilege escalation means. Windows processes often leverage these API functions to perform tasks that require reusable system resources. Windows API functions are typically stored in dynamic-link libraries (DLLs) as exported functions. CitationEnterprise ATT&CK

One type of hooking seen in ICS involves redirecting calls to these functions via import address table (IAT) hooking. IAT hooking uses modifications to a process IAT, where pointers to imported API functions are stored. [2]

Adversaries may seek to capture process values related to the inputs and outputs of a PLC. During the scan cycle, a PLC reads the status of all inputs and stores them in an image table. [1] The image table is the PLCs internal storage location where values of inputs/outputs for one scan are stored while it executes the user program. After the PLC has solved the entire logic program, it updates the output image table. The contents of this output image table are written to the corresponding output points in I/O Modules.

The Input and Output Image tables described above make up the I/O Image on a PLC. This image is used by the user program instead of directly interacting with physical I/O. [2]

Adversaries may collect the I/O Image state of a PLC by utilizing a devices Native API to access the memory regions directly. The collection of the PLCs I/O state could be used to replace values or inform future stages of an attack.

Adversaries may attempt to remove indicators of their presence on a system in an effort to cover their tracks. In cases where an adversary may feel detection is imminent, they may try to overwrite, delete, or cover up changes they have made to the device.

Adversaries may target insecure credentials as a means to persist on a system or device or move laterally from one system or device to another. Insecure credentials may appear as default credentials which are pre-configured credentials on a system, device, or software that are well-known in documentation or hard-coded credentials which are built into the system, device, or software that cannot be changed or not easily changed because of the impact on control processes.[1][2][3] Adversaries often times use insecure credentials to evade detection as they are typically forgotten about by system and device owners.

Adversaries may gain access into industrial environments through systems exposed directly to the internet for remote access rather than through External Remote Services. Internet Accessible Devices are exposed to the internet unintentionally or intentionally without adequate protections. This may allow for adversaries to move directly into the control system network. Access onto these devices is accomplished without the use of exploits, these would be represented within the Exploit Public-Facing Application technique.

Adversaries may leverage built in functions for remote access which may not be protected or utilize minimal legacy protections that may be targeted. [1] These services may be discoverable through the use of online scanning tools.

In the case of the Bowman dam incident, adversaries leveraged access to the dam control network through a cellular modem. Access to the device was protected by password authentication, although the application was vulnerable to brute forcing. [1] [2] [3]

In Trend Micros manufacturing deception operations adversaries were detected leveraging direct internet access to an ICS environment through the exposure of operational protocols such as Siemens S7, Omron FINS, and EtherNet/IP, in addition to misconfigured VNC access. [4]

Adversaries may transfer tools or other files from one system to another to stage adversary tools or other files over the course of an operation.CitationEnterprise ATT&CK Copying of files may also be performed laterally between internal victim systems to support Lateral Movement with remote Execution using inherent file sharing protocols such as file sharing over SMB to connected network shares.CitationEnterprise ATT&CK

In control systems environments, malware may use SMB and other file sharing protocols to move laterally through industrial networks.

Adversaries may manipulate the I/O image of PLCs through various means to prevent them from functioning as expected. Methods of I/O image manipulation may include overriding the I/O table via direct memory manipulation or using the override function used for testing PLC programs. [1] During the scan cycle, a PLC reads the status of all inputs and stores them in an image table. [2] The image table is the PLCs internal storage location where values of inputs/outputs for one scan are stored while it executes the user program. After the PLC has solved the entire logic program, it updates the output image table. The contents of this output image table are written to the corresponding output points in I/O Modules.

One of the unique characteristics of PLCs is their ability to override the status of a physical discrete input or to override the logic driving a physical output coil and force the output to a desired status.

Adversaries may use masquerading to disguise a malicious application or executable as another file, to avoid operator and engineer suspicion. Possible disguises of these masquerading files can include commonly found programs, expected vendor executables and configuration files, and other commonplace application and naming conventions. By impersonating expected and vendor-relevant files and applications, operators and engineers may not notice the presence of the underlying malicious content and possibly end up running those masquerading as legitimate functions.

Applications and other files commonly found on Windows systems or in engineering workstations have been impersonated before. This can be as simple as renaming a file to effectively disguise it in the ICS environment.

Adversaries may modify alarm settings to prevent alerts that may inform operators of their presence or to prevent responses to dangerous and unintended scenarios. Reporting messages are a standard part of data acquisition in control systems. Reporting messages are used as a way to transmit system state information and acknowledgements that specific actions have occurred. These messages provide vital information for the management of a physical process, and keep operators, engineers, and administrators aware of the state of system devices and physical processes.

If an adversary is able to change the reporting settings, certain events could be prevented from being reported. This type of modification can also prevent operators or devices from performing actions to keep the system in a safe state. If critical reporting messages cannot trigger these actions then a Impact could occur.

In ICS environments, the adversary may have to use Alarm Suppression or contend with multiple alarms and/or alarm propagation to achieve a specific goal to evade detection or prevent intended responses from occurring. [1] Methods of suppression often rely on modification of alarm settings, such as modifying in memory code to fixed values or tampering with assembly level instruction code.

Adversaries may modify the tasking of a controller to allow for the execution of their own programs. This can allow an adversary to manipulate the execution flow and behavior of a controller.

According to 61131-3, the association of a Task with a Program Organization Unit (POU) defines a task association. [1] An adversary may modify these associations or create new ones to manipulate the execution flow of a controller. Modification of controller tasking can be accomplished using a Program Download in addition to other types of program modification such as online edit and program append.

Tasks have properties, such as interval, frequency and priority to meet the requirements of program execution. Some controller vendors implement tasks with implicit, pre-defined properties whereas others allow for these properties to be formulated explicitly. An adversary may associate their program with tasks that have a higher priority or execute associated programs more frequently. For instance, to ensure cyclic execution of their program on a Siemens controller, an adversary may add their program to the task, Organization Block 1 (OB1).

Firmware is low-level software embedded in hardware that enables systems and devices to function properly and is commonly found in ICS environments. Adversaries may modify firmware on a system or device by installing malicious or vulnerable versions that enable them to achieve objectives such as Persistence, Impair Process Control, and Inhibit Response Function.

Adversaries may modify system and device firmware by using the built-in firmware update functionality which may support local or remote installation. The malicious or vulnerable firmware may be delivered via Replication Through Removable Media, Supply Chain Compromise, or Remote Services. Once installed, the malicious or vulnerable firmware could be used to provide Rootkit and Hooking functionality, Exploitation for Privilege Escalation, or Denial of Service.[1]

Adversaries may modify parameters used to instruct industrial control system devices. These devices operate via programs that dictate how and when to perform actions based on such parameters. Such parameters can determine the extent to which an action is performed and may specify additional options. For example, a program on a control system device dictating motor processes may take a parameter defining the total number of seconds to run that motor.

An adversary can potentially modify these parameters to produce an outcome outside of what was intended by the operators. By modifying system and process critical parameters, the adversary may cause Impact to equipment and/or control processes. Modified parameters may be turned into dangerous, out-of-bounds, or unexpected values from typical operations. For example, specifying that a process run for more or less time than it should, or dictating an unusually high, low, or invalid value as a parameter.

Adversaries may modify or add a program on a controller to affect how it interacts with the physical process, peripheral devices and other hosts on the network. Modification to controller programs can be accomplished using a Program Download in addition to other types of program modification such as online edit and program append.

Program modification encompasses the addition and modification of instructions and logic contained in Program Organization Units (POU) [1] and similar programming elements found on controllers. This can include, for example, adding new functions to a controller, modifying the logic in existing functions and making new calls from one function to another.

Some programs may allow an adversary to interact directly with the native API of the controller to take advantage of obscure features or vulnerabilities.

Adversaries may install malicious or vulnerable firmware onto modular hardware devices. Control system devices often contain modular hardware devices. These devices may have their own set of firmware that is separate from the firmware of the main control system equipment.

This technique is similar to System Firmware, but is conducted on other system components that may not have the same capabilities or level of integrity checking. Although it results in a device re-image, malicious device firmware may provide persistent access to remaining devices.[1]

An easy point of access for an adversary is the Ethernet card, which may have its own CPU, RAM, and operating system. The adversary may attack and likely exploit the computer on an Ethernet card. Exploitation of the Ethernet card computer may enable the adversary to accomplish additional attacks, such as the following:[1]

* Delayed Attack - The adversary may stage an attack in advance and choose when to launch it, such as at a particularly damaging time. * Brick the Ethernet Card - Malicious firmware may be programmed to result in an Ethernet card failure, requiring a factory return. * Random Attack or Failure - The adversary may load malicious firmware onto multiple field devices. Execution of an attack and the time it occurs is generated by a pseudo-random number generator. * A Field Device Worm - The adversary may choose to identify all field devices of the same model, with the end goal of performing a device-wide compromise. * Attack Other Cards on the Field Device - Although it is not the most important module in a field device, the Ethernet card is most accessible to the adversary and malware. Compromise of the Ethernet card may provide a more direct route to compromising other modules, such as the CPU module.

Adversaries may gather information about the physical process state. This information may be used to gain more information about the process itself or used as a trigger for malicious actions. The sources of process state information may vary such as, OPC tags, historian data, specific PLC block information, or network traffic.

Adversaries may perform multicast discovery requests which is when one system or device sends messages to all systems and devices in a pre-defined group on a network (or subnet) and then waits for a response. If a response is received that means the system or device that responded is live and can communicate over that protocol. Multicast discovery tends to be stealthier than broadcast discovery because every system or device on the network (or subnet) is not being messaged.

One common OT protocol that has a multicast discovery mechanism is the Process Field Network (PROFINET) Discovery and Configuration Protocol (DCP) with its Identify All requests.[1]

Adversaries may directly interact with the native OS application programming interface (API) to access system functions. Native APIs provide a controlled means of calling low-level OS services within the kernel, such as those involving hardware/devices, memory, and processes. [1] These native APIs are leveraged by the OS during system boot (when other system components are not yet initialized) as well as carrying out tasks and requests during routine operations.

Functionality provided by native APIs are often also exposed to user-mode applications via interfaces and libraries. For example, functions such as memcpy and direct operations on memory registers can be used to modify user and system memory space.

Adversaries may perform network connection enumeration to discover information about device communication patterns. If an adversary can inspect the state of a network connection with tools, such as Netstat[1], in conjunction with System Firmware, then they can determine the role of certain devices on the network [2]. The adversary can also use Network Sniffing to watch network traffic for details about the source, destination, protocol, and content.

Network sniffing is the practice of using a network interface on a computer system to monitor or capture information CitationEnterprise ATT&CK January 2018 regardless of whether it is the specified destination for the information.

An adversary may attempt to sniff the traffic to gain information about the target. This information can vary in the level of importance. Relatively unimportant information is general communications to and from machines. Relatively important information would be login information. User credentials may be sent over an unencrypted protocol, such as Telnet, that can be captured and obtained through network packet analysis.

In addition, ARP and Domain Name Service (DNS) poisoning can be used to capture credentials to websites, proxies, and internal systems by redirecting traffic to an adversary.

Adversaries may execute an online edit of a PLC to update parts of an existing program. It does not require stopping the PLC which allows it to continue running during transfer and reconfiguration without interruption to process control. Adversaries may leverage this approach to minimize downtime and evade detection.

The ability to perform an online edit to the PLC typically relies on access to a workstation with the vendor-specific PLC programming software installed.

Adversaries may collect point and tag values to gain a more comprehensive understanding of the process environment. Points may be values such as inputs, memory locations, outputs or other process specific variables. [1] Tags are the identifiers given to points for operator convenience.

Collecting such tags provides valuable context to environmental points and enables an adversary to map inputs, outputs, and other values to their control processes. Understanding the points being collected may inform an adversary on which processes and values to keep track of over the course of an operation.

Adversaries may perform a port scan on a system, device, or network to identify live hosts, enumerate open ports and running services, identify operating systems, and map out the network.[1] The results of a port scan may inform adversary Discovery, Lateral Movement, and vulnerability exploitation decisions (Exploitation for Evasion, Exploitation for Privilege Escalation, Exploitation of Remote Services).

Some common tools for executing a port scan include `nmap`, `netcat`, and the Advanced Port Scanner.

Adversaries may execute a program append to a PLC to update parts of an existing program. It may or may not require stopping the PLC which may allow it to continue running during transfer and reconfiguration without interruption to process control. Adversaries may leverage this approach to minimize downtime and evade detection.

The ability to perform a program append to the PLC typically relies on access to a workstation with the vendor-specific PLC programming software installed.

Adversaries may perform a program download to transfer a user program to a controller.

Variations of program download, such as online edit and program append, allow a controller to continue running during the transfer and reconfiguration process without interruption to process control. However, before starting a full program download (i.e., download all) a controller may need to go into a stop state. This can have negative consequences on the physical process, especially if the controller is not able to fulfill a time-sensitive action. Adversaries may choose to avoid a download all in favor of an online edit or program append to avoid disrupting the physical process. An adversary may need to use the technique Detect Operating Mode or Change Operating Mode to make sure the controller is in the proper mode to accept a program download.

The granularity of control to transfer a user program in whole or parts is dictated by the management protocol (e.g., S7CommPlus, TriStation) and underlying controller API. Thus, program download is a high-level term for the suite of vendor-specific API calls used to configure a controllers user program memory space.

Modify Controller Tasking and Modify Program represent the configuration changes that are transferred to a controller via a program download.

Adversaries may attempt to upload a program from a PLC to gather information about an industrial process. Uploading a program may allow them to acquire and study the underlying logic. Methods of program upload include vendor software, which enables the user to upload and read a program running on a PLC. This software can be used to upload the target program to a workstation, jump box, or an interfacing device.

Adversaries may leverage remote services to move between assets and network segments. These services are often used to allow operators to interact with systems remotely within the network, some examples are RDP, SMB, SSH, and other similar mechanisms. [1] [2] [3]

Remote services could be used to support remote access, data transmission, authentication, name resolution, and other remote functions. Further, remote services may be necessary to allow operators and administrators to configure systems within the network from their engineering or management workstations. An adversary may use this technique to access devices which may be dual-homed [1] to multiple network segments, and can be used for Program Download or to execute attacks on control devices directly through Valid Accounts.

Specific remote services (RDP & VNC) may be a precursor to enable Graphical User Interface execution on devices such as HMIs or engineering workstation software.

Based on incident data, CISA and FBI assessed that Chinese state-sponsored actors also compromised various authorized remote access channels, including systems designed to transfer data and/or allow access between corporate and ICS networks. [4]

Adversaries may attempt to get a listing of other systems by IP address, hostname, or other logical identifier on a network that may be used for subsequent Lateral Movement or Discovery techniques. Functionality could exist within adversary tools to enable this, but utilities available on the operating system or vendor software could also be used.CitationEnterprise ATT&CK January 2018

An adversary may attempt to get detailed information about remote systems and their peripherals, such as make/model, role, and configuration. Adversaries may use information from Remote System Information Discovery to aid in targeting and shaping follow-on behaviors. For example, the system's operational role and model information can dictate whether it is a relevant target for the adversary's operational objectives. In addition, the system's configuration may be used to scope subsequent technique usage.

Requests for system information are typically implemented using automation and management protocols and are often automatically requested by vendor software during normal operation. This information may be used to tailor management actions, such as program download and system or module firmware. An adversary may leverage this same information by issuing calls directly to the system's API.