The adversary is trying to run code or manipulate system functions, parameters, and data in an unauthorized way.
Execution consists of techniques that result in adversary-controlled code running on a local or remote system, device, or other asset. This execution may also rely on unknowing end users or the manipulation of device operating modes to run. Adversaries may infect remote targets with programmed executables or malicious project files that operate according to specified behavior and may alter expected device behavior in subtle ways. Commands for execution may also be issued from command-line interfaces, APIs, GUIs, or other available interfaces. Techniques that run malicious code may also be paired with techniques from other tactics, particularly to aid network Discovery and Collection, impact operations, and inhibit response functions.
Techniques in this Tactics Category
Below is a list of all the Execution techniques in ATT&CK for ICS:
|Change Operating Mode||Execution|
|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 controller’s 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 controller’s 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:
|Command-Line Interface||Execution||Adversaries may utilize command-line interfaces (CLIs) to interact with systems and execute commands. CLIs provide a means of interacting with computer systems and are a common feature across many types of platforms and devices within control systems environments.5 Adversaries may also use CLIs to install and run new software, including malicious tools that may be installed over the course of an operation.
CLIs are typically accessed locally, but can also be exposed via services, such as SSH, Telnet, and RDP. Commands that are executed in the CLI execute with the current permissions level of the process running the terminal emulator, unless the command specifies a change in permissions context.Many controllers have CLI interfaces for management purposes.
|Execution through API||Execution||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.|
|Graphical User Interface||Execution||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 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.6 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’s IAT, where pointers to imported API functions are stored.7|
|Modify Controller Tasking||Execution||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.8 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).
|Native API||Execution||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.9 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.|
|Scripting||Execution||Adversaries may use scripting languages to execute arbitrary code in the form of a pre-written script or in the form of user-supplied code to an interpreter. Scripting languages are programming languages that differ from compiled languages, in that scripting languages use an interpreter, instead of a compiler. These interpreters read and compile part of the source code just before it is executed, as opposed to compilers, which compile each and every line of code to an executable file. Scripting allows software developers to run their code on any system where the interpreter exists. This way, they can distribute one package, instead of precompiling executables for many different systems. Scripting languages, such as Python, have their interpreters shipped as a default with many Linux distributions. In addition to being a useful tool for developers and administrators, scripting language interpreters may be abused by the adversary to execute code in the target environment. Due to the nature of scripting languages, this allows for weaponized code to be deployed to a target easily, and leaves open the possibility of on-the-fly scripting to perform a task.|
|User Execution||Execution||Adversaries may rely on a targeted organizations’ user interaction for the execution of malicious code. User interaction may consist of installing applications, opening email attachments, or granting higher permissions to documents. Adversaries may embed malicious code or visual basic code into files such as Microsoft Word and Excel documents or software installers.10 Execution of this code requires that the user enable scripting or write access within the document. Embedded code may not always be noticeable to the user especially in cases of trojanized software.11|
- N.A.. (2017, October). What are the different operating modes in PLC?. Retrieved January 28, 2021.
- Omron. (n.d.). PLC Different Operating Modes. Retrieved January 28, 2021.
- Machine Information Systems. (2007). How PLCs Work. Retrieved January 28, 2021.
- PLCgurus. (2021). PLC Basics – Modes Of Operation. Retrieved January 28, 2021.
- Enterprise ATT&CK. (2018, January 11). Command-Line Interface. Retrieved May 17, 2018.
- Enterprise ATT&CK. (n.d.). Hooking. Retrieved October 27, 2019.
- Nicolas Falliere, Liam O Murchu, Eric Chien. (2011, February). W32.Stuxnet Dossier (Version 1.4). Retrieved September 22, 2017.
- IEC. (2013, February 20). IEC 61131-3:2013 Programmable controllers - Part 3: Programming languages. Retrieved October 22, 2019.
- The MITRE Corporation. (2017, May 31). ATT&CK T1106: Native API. Retrieved April 26, 2021.
- Booz Allen Hamilton. (n.d.). When The Lights Went Out. Retrieved October 22, 2019.
- Daavid Hentunen, Antti Tikkanen. (2014, June 23). Havex Hunts For ICS/SCADA Systems. Retrieved April 1, 2019.