The adversary is trying to prevent your safety, protection, quality assurance, and operator intervention functions from responding to a failure, hazard, or unsafe state. Inhibit Response Function consists of techniques that adversaries use to hinder the safeguards put in place for processes and products. This may involve the inhibition of safety, protection, quality assurance, or operator intervention functions to disrupt safeguards that aim to prevent the loss of life, destruction of equipment, and disruption of production. These techniques aim to actively deter and prevent expected alarms and responses that arise due to statuses in the ICS environment. Adversaries may modify or update system logic, or even outright prevent responses with a denial-of-service. They may result in the prevention, destruction, manipulation, or modification of programs, logic, devices, and communications. As prevention functions are generally dormant, reporting and processing functions can appear fine, but may have been altered to prevent failure responses in dangerous scenarios. Unlike [Evasion](https://attack.mitre.org/tactics/TA0103), Inhibit Response Function techniques may be more intrusive, such as actively preventing responses to a known dangerous scenario. Adversaries may use these techniques to follow through with or provide cover for [Impact](https://attack.mitre.org/tactics/TA0105) techniques.

Subissues

Issuelinks
Service Stop Adversaries may stop or disable services on a system to render those services unavailable to legitimate users. Stopping critical services can inhibit or stop response to an incident or aid in the adversary's overall objectives to cause damage to the environment. (Citation: Enterprise ATT&CK) Services may not allow for modification of their data stores while running. Adversaries may stop services in order to conduct Data Destruction. (Citation: Enterprise ATT&CK)
Activate Firmware Update Mode 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.
Denial of Service 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. (Citation: ICS-CERT April 2017) 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](https://attack.mitre.org/techniques/T0888). There are examples of adversaries remotely causing a [Device Restart/Shutdown](https://attack.mitre.org/techniques/T0816) by exploiting a vulnerability that induces uncontrolled resource consumption. (Citation: ICS-CERT August 2018) (Citation: Common Weakness Enumeration January 2019) (Citation: MITRE March 2018)
Device Restart/Shutdown 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.
Alarm Suppression 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. (Citation: Jos Wetzels, Marina Krotofil 2019) 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. (Citation: Jos Wetzels, Marina Krotofil 2019) 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.
Block Operational Technology Message 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.(Citation: Bonnie Zhu, Anthony Joseph, Shankar Sastry 2011)(Citation: Electricity Information Sharing and Analysis Center; SANS Industrial Control Systems March 2016) Adversaries may block communications by either making modifications to software ([System Firmware](https://attack.mitre.org/techniques/T0857), [Module Firmware](https://attack.mitre.org/techniques/T0839), [Hooking](https://attack.mitre.org/techniques/T0874), and [Rootkit](https://attack.mitre.org/techniques/T0851)) and services ([Service Stop](https://attack.mitre.org/techniques/T0881), [Denial of Service](https://attack.mitre.org/techniques/T0814)) 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](https://attack.mitre.org/techniques/T0830) attack.
Manipulate I/O Image 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. (Citation: Dr. Kelvin T. Erickson December 2010) During the scan cycle, a PLC reads the status of all inputs and stores them in an image table. (Citation: Nanjundaiah, Vaidyanath) 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.
Rootkit Adversaries may deploy rootkits to hide the presence of programs, files, network connections, services, drivers, and other system components. Rootkits are programs that hide the existence of malware by intercepting and modifying operating-system API calls that supply system information. Rootkits or rootkit-enabling functionality may reside at the user or kernel level in the operating system, or lower. (Citation: Enterprise ATT&CK January 2018) Firmware rootkits that affect the operating system yield nearly full control of the system. While firmware rootkits are normally developed for the main processing board, they can also be developed for the I/O that is attached to an asset. Compromise of this firmware allows the modification of all of the process variables and functions the module engages in. This may result in commands being disregarded and false information being fed to the main device. By tampering with device processes, an adversary may inhibit its expected response functions and possibly enable [Impact](https://attack.mitre.org/tactics/TA0105).
Data Destruction 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. (Citation: Enterprise 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.
Modify Firmware 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](https://attack.mitre.org/tactics/TA0110), [Impair Process Control](https://attack.mitre.org/tactics/TA0106), and [Inhibit Response Function](https://attack.mitre.org/tactics/TA0107). 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](https://attack.mitre.org/techniques/T0847), [Supply Chain Compromise](https://attack.mitre.org/techniques/T0862), or [Remote Services](https://attack.mitre.org/techniques/T0886). Once installed, the malicious or vulnerable firmware could be used to provide [Rootkit](https://attack.mitre.org/techniques/T0851) and [Hooking](https://attack.mitre.org/techniques/T0874) functionality, [Exploitation for Privilege Escalation](https://attack.mitre.org/techniques/T0890), or [Denial of Service](https://attack.mitre.org/techniques/T0814).(Citation: Basnight, Zachry, et al.)
Modify Control Logic Adversaries may place malicious code in a system, which can cause the system to malfunction by modifying its control logic. Control system devices use programming languages (e.g. relay ladder logic) to control physical processes by affecting actuators, which cause machines to operate, based on environment sensor readings. These devices often include the ability to perform remote control logic updates. Program code is normally edited in a vendor-specific Integrated Development Environment (IDE) that relies on proprietary tools and features. These IDEs allow an engineer to perform host target development and may have the ability to run the code on the machine it is programmed for. The IDE will transmit the control logic to the testing device, and will perform the required device-specific functions to apply the changes and make them active. An adversary may attempt to use this host target IDE to modify device control logic. Even though proprietary tools are often used to edit and update control logic, the process can usually be reverse-engineered and reproduced with open-source tools. An adversary can de-calibrate a sensor by removing functions in control logic that account for sensor error. This can be used to change a control process without actually spoofing command messages to a controller or device. It is believed this process happened in the lesser known over-pressurizer attacks build into Stuxnet. Pressure sensors are not perfect at translating pressure into an analog output signal, but their errors can be corrected by calibration. The pressure controller can be told what the “real” pressure is for given analog signals and then automatically linearize the measurement to what would be the “real” pressure. If the linearization is overwritten by malicious code on the S7-417 controller, analog pressure readings will be “corrected” during the attack by the pressure controller, which then interprets all analog pressure readings as perfectly normal pressure no matter how high or low their analog values are. The pressure controller then acts accordingly by never opening the stage exhaust valves. In the meantime, actual pressure keeps rising. (Citation: Stuxnet - Langner - 201311) In the Maroochy Attack, Vitek Boden gained remote computer access to the control system and altered data so that whatever function should have occurred at affected pumping stations did not occur or occurred in a different way. The software program installed in the laptop was one developed by Hunter Watertech for its use in changing configurations in the PDS computers. This ultimately led to 800,000 liters of raw sewage being spilled out into the community. (Citation: Maroochy - MITRE - 200808)
Modify Alarm Settings 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](https://attack.mitre.org/tactics/TA0105) could occur. In ICS environments, the adversary may have to use [Alarm Suppression](https://attack.mitre.org/techniques/T0878) or contend with multiple alarms and/or alarm propagation to achieve a specific goal to evade detection or prevent intended responses from occurring. (Citation: Jos Wetzels, Marina Krotofil 2019) 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.
Change Credential 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. (Citation: German BAS Lockout Dec 2021)
Block Communications 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.(Citation: Bonnie Zhu, Anthony Joseph, Shankar Sastry 2011) Adversaries may block communications by either making modifications to software ([System Firmware](https://attack.mitre.org/techniques/T0857), [Module Firmware](https://attack.mitre.org/techniques/T0839), [Hooking](https://attack.mitre.org/techniques/T0874), and [Rootkit](https://attack.mitre.org/techniques/T0851)) and services ([Service Stop](https://attack.mitre.org/techniques/T0881), [Denial of Service](https://attack.mitre.org/techniques/T0814)) 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](https://attack.mitre.org/techniques/T0830) attack.

Linked Issues

Issuelinks
is related to Tactics
is part of ICS ATT&CK
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