NIST SP 800-53 Rev. 5 Common Control Library

NIST control statement

Develop a system-level continuous monitoring strategy and implement continuous monitoring in accordance with the organization-level continuous monitoring strategy that includes: a. Establishing the following system-level metrics to be monitored: [Assignment: system-level metrics]; b. Establishing [Assignment: frequencies] for monitoring and [Assignment: frequencies] for assessment of control effectiveness; c. Ongoing control assessments in accordance with the continuous monitoring strategy; d. Ongoing monitoring of system and organization-defined metrics in accordance with the continuous monitoring strategy; e. Correlation and analysis of information generated by control assessments and monitoring; f. Response actions to address results of the analysis of control assessment and monitoring information; and g. Reporting the security and privacy status of the system to [Assignment: organization-defined personnel or roles] [Assignment: organization-defined frequency].

Discussion

Continuous monitoring at the system level facilitates ongoing awareness of the system security and privacy posture to support organizational risk management decisions. The terms "continuous" and "ongoing" imply that organizations assess and monitor their controls and risks at a frequency sufficient to support risk-based decisions. Different types of controls may require different monitoring frequencies. The results of continuous monitoring generate risk response actions by organizations. When monitoring the effectiveness of multiple controls that have been grouped into capabilities, a root-cause analysis may be needed to determine the specific control that has failed. Continuous monitoring programs allow organizations to maintain the authorizations of systems and common controls in highly dynamic environments of operation with changing mission and business needs, threats, vulnerabilities, and technologies. Having access to security and privacy information on a continuing basis through reports and dashboards gives organizational officials the ability to make effective and timely risk management decisions, including ongoing authorization decisions. Automation supports more frequent updates to hardware, software, and firmware inventories, authorization packages, and other system information. Effectiveness is further enhanced when continuous monitoring outputs are formatted to provide information that is specific, measurable, actionable, relevant, and timely. Continuous monitoring activities are scaled in accordance with the security categories of systems. Monitoring requirements, including the need for specific monitoring, may be referenced in other controls and control enhancements, such as [AC-2g](#ac-2_smt.g), [AC-2(7)](#ac-2.7), [AC-2(12)(a)](#ac-2.12_smt.a), [AC-2(7)(b)](#ac-2.7_smt.b), [AC-2(7)(c)](#ac-2.7_smt.c), [AC-17(1)](#ac-17.1), [AT-4a](#at-4_smt.a), [AU-13](#au-13), [AU-13(1)](#au-13.1), [AU-13(2)](#au-13.2), [CM-3f](#cm-3_smt.f), [CM-6d](#cm-6_smt.d), [CM-11c](#cm-11_smt.c), [IR-5](#ir-5), [MA-2b](#ma-2_smt.b), [MA-3a](#ma-3_smt.a), [MA-4a](#ma-4_smt.a), [PE-3d](#pe-3_smt.d), [PE-6](#pe-6), [PE-14b](#pe-14_smt.b), [PE-16](#pe-16), [PE-20](#pe-20), [PM-6](#pm-6), [PM-23](#pm-23), [PM-31](#pm-31), [PS-7e](#ps-7_smt.e), [SA-9c](#sa-9_smt.c), [SR-4](#sr-4), [SC-5(3)(b)](#sc-5.3_smt.b), [SC-7a](#sc-7_smt.a), [SC-7(24)(b)](#sc-7.24_smt.b), [SC-18b](#sc-18_smt.b), [SC-43b](#sc-43_smt.b) , and [SI-4](#si-4).

NIST control statement

Centrally manage [Assignment: controls and related processes].

Discussion

Central management refers to organization-wide management and implementation of selected controls and processes. This includes planning, implementing, assessing, authorizing, and monitoring the organization-defined, centrally managed controls and processes. As the central management of controls is generally associated with the concept of common (inherited) controls, such management promotes and facilitates standardization of control implementations and management and the judicious use of organizational resources. Centrally managed controls and processes may also meet independence requirements for assessments in support of initial and ongoing authorizations to operate and as part of organizational continuous monitoring. Automated tools (e.g., security information and event management tools or enterprise security monitoring and management tools) can improve the accuracy, consistency, and availability of information associated with centrally managed controls and processes. Automation can also provide data aggregation and data correlation capabilities; alerting mechanisms; and dashboards to support risk-based decision-making within the organization. As part of the control selection processes, organizations determine the controls that may be suitable for central management based on resources and capabilities. It is not always possible to centrally manage every aspect of a control. In such cases, the control can be treated as a hybrid control with the control managed and implemented centrally or at the system level. The controls and control enhancements that are candidates for full or partial central management include but are not limited to: [AC-2(1)](#ac-2.1), [AC-2(2)](#ac-2.2), [AC-2(3)](#ac-2.3), [AC-2(4)](#ac-2.4), [AC-4(all)](#ac-4), [AC-17(1)](#ac-17.1), [AC-17(2)](#ac-17.2), [AC-17(3)](#ac-17.3), [AC-17(9)](#ac-17.9), [AC-18(1)](#ac-18.1), [AC-18(3)](#ac-18.3), [AC-18(4)](#ac-18.4), [AC-18(5)](#ac-18.5), [AC-19(4)](#ac-19.4), [AC-22](#ac-22), [AC-23](#ac-23), [AT-2(1)](#at-2.1), [AT-2(2)](#at-2.2), [AT-3(1)](#at-3.1), [AT-3(2)](#at-3.2), [AT-3(3)](#at-3.3), [AT-4](#at-4), [AU-3](#au-3), [AU-6(1)](#au-6.1), [AU-6(3)](#au-6.3), [AU-6(5)](#au-6.5), [AU-6(6)](#au-6.6), [AU-6(9)](#au-6.9), [AU-7(1)](#au-7.1), [AU-7(2)](#au-7.2), [AU-11](#au-11), [AU-13](#au-13), [AU-16](#au-16), [CA-2(1)](#ca-2.1), [CA-2(2)](#ca-2.2), [CA-2(3)](#ca-2.3), [CA-3(1)](#ca-3.1), [CA-3(2)](#ca-3.2), [CA-3(3)](#ca-3.3), [CA-7(1)](#ca-7.1), [CA-9](#ca-9), [CM-2(2)](#cm-2.2), [CM-3(1)](#cm-3.1), [CM-3(4)](#cm-3.4), [CM-4](#cm-4), [CM-6](#cm-6), [CM-6(1)](#cm-6.1), [CM-7(2)](#cm-7.2), [CM-7(4)](#cm-7.4), [CM-7(5)](#cm-7.5), [CM-8(all)](#cm-8), [CM-9(1)](#cm-9.1), [CM-10](#cm-10), [CM-11](#cm-11), [CP-7(all)](#cp-7), [CP-8(all)](#cp-8), [SC-43](#sc-43), [SI-2](#si-2), [SI-3](#si-3), [SI-4(all)](#si-4), [SI-7](#si-7), [SI-8](#si-8).

NIST control statement

Develop an organization-wide continuous monitoring strategy and implement continuous monitoring programs that include: a. Establishing the following organization-wide metrics to be monitored: [Assignment: metrics]; b. Establishing [Assignment: monitoring frequencies] and [Assignment: assessment frequencies] for control effectiveness; c. Ongoing monitoring of organizationally-defined metrics in accordance with the continuous monitoring strategy; d. Correlation and analysis of information generated by control assessments and monitoring; e. Response actions to address results of the analysis of control assessment and monitoring information; and f. Reporting the security and privacy status of organizational systems to [Assignment: organization-defined personnel or roles] [Assignment: organization-defined frequency].

Discussion

Continuous monitoring at the organization level facilitates ongoing awareness of the security and privacy posture across the organization to support organizational risk management decisions. The terms "continuous" and "ongoing" imply that organizations assess and monitor their controls and risks at a frequency sufficient to support risk-based decisions. Different types of controls may require different monitoring frequencies. The results of continuous monitoring guide and inform risk response actions by organizations. Continuous monitoring programs allow organizations to maintain the authorizations of systems and common controls in highly dynamic environments of operation with changing mission and business needs, threats, vulnerabilities, and technologies. Having access to security- and privacy-related information on a continuing basis through reports and dashboards gives organizational officials the capability to make effective, timely, and informed risk management decisions, including ongoing authorization decisions. To further facilitate security and privacy risk management, organizations consider aligning organization-defined monitoring metrics with organizational risk tolerance as defined in the risk management strategy. Monitoring requirements, including the need for monitoring, may be referenced in other controls and control enhancements such as, [AC-2g](#ac-2_smt.g), [AC-2(7)](#ac-2.7), [AC-2(12)(a)](#ac-2.12_smt.a), [AC-2(7)(b)](#ac-2.7_smt.b), [AC-2(7)(c)](#ac-2.7_smt.c), [AC-17(1)](#ac-17.1), [AT-4a](#at-4_smt.a), [AU-13](#au-13), [AU-13(1)](#au-13.1), [AU-13(2)](#au-13.2), [CA-7](#ca-7), [CM-3f](#cm-3_smt.f), [CM-6d](#cm-6_smt.d), [CM-11c](#cm-11_smt.c), [IR-5](#ir-5), [MA-2b](#ma-2_smt.b), [MA-3a](#ma-3_smt.a), [MA-4a](#ma-4_smt.a), [PE-3d](#pe-3_smt.d), [PE-6](#pe-6), [PE-14b](#pe-14_smt.b), [PE-16](#pe-16), [PE-20](#pe-20), [PM-6](#pm-6), [PM-23](#pm-23), [PS-7e](#ps-7_smt.e), [SA-9c](#sa-9_smt.c), [SC-5(3)(b)](#sc-5.3_smt.b), [SC-7a](#sc-7_smt.a), [SC-7(24)(b)](#sc-7.24_smt.b), [SC-18b](#sc-18_smt.b), [SC-43b](#sc-43_smt.b), [SI-4](#si-4).

NIST control statement

Prevent unauthorized and unintended information transfer via shared system resources.

Discussion

Preventing unauthorized and unintended information transfer via shared system resources stops information produced by the actions of prior users or roles (or the actions of processes acting on behalf of prior users or roles) from being available to current users or roles (or current processes acting on behalf of current users or roles) that obtain access to shared system resources after those resources have been released back to the system. Information in shared system resources also applies to encrypted representations of information. In other contexts, control of information in shared system resources is referred to as object reuse and residual information protection. Information in shared system resources does not address information remanence, which refers to the residual representation of data that has been nominally deleted; covert channels (including storage and timing channels), where shared system resources are manipulated to violate information flow restrictions; or components within systems for which there are only single users or roles.

NIST control statement

Withdrawn in this source release; review the official source for disposition.

NIST control statement

Prevent unauthorized information transfer via shared resources in accordance with [Assignment: procedures] when system processing explicitly switches between different information classification levels or security categories.

Discussion

Changes in processing levels can occur during multilevel or periods processing with information at different classification levels or security categories. It can also occur during serial reuse of hardware components at different classification levels. Organization-defined procedures can include approved sanitization processes for electronically stored information.

NIST control statement

Protect external and internal [Assignment: organization-defined wireless links] from the following signal parameter attacks: [Assignment: organization-defined types of signal parameter attacks or references to sources for such attacks].

Discussion

Wireless link protection applies to internal and external wireless communication links that may be visible to individuals who are not authorized system users. Adversaries can exploit the signal parameters of wireless links if such links are not adequately protected. There are many ways to exploit the signal parameters of wireless links to gain intelligence, deny service, or spoof system users. Protection of wireless links reduces the impact of attacks that are unique to wireless systems. If organizations rely on commercial service providers for transmission services as commodity items rather than as fully dedicated services, it may not be possible to implement wireless link protections to the extent necessary to meet organizational security requirements.

NIST control statement

Implement cryptographic mechanisms that achieve [Assignment: level of protection] against the effects of intentional electromagnetic interference.

Discussion

The implementation of cryptographic mechanisms for electromagnetic interference protects systems against intentional jamming that might deny or impair communications by ensuring that wireless spread spectrum waveforms used to provide anti-jam protection are not predictable by unauthorized individuals. The implementation of cryptographic mechanisms may also coincidentally mitigate the effects of unintentional jamming due to interference from legitimate transmitters that share the same spectrum. Mission requirements, projected threats, concept of operations, and laws, executive orders, directives, regulations, policies, and standards determine levels of wireless link availability, cryptography needed, and performance.

NIST control statement

Implement cryptographic mechanisms to reduce the detection potential of wireless links to [Assignment: level of reduction].

Discussion

The implementation of cryptographic mechanisms to reduce detection potential is used for covert communications and to protect wireless transmitters from geo-location. It also ensures that the spread spectrum waveforms used to achieve a low probability of detection are not predictable by unauthorized individuals. Mission requirements, projected threats, concept of operations, and applicable laws, executive orders, directives, regulations, policies, and standards determine the levels to which wireless links are undetectable.

NIST control statement

Implement cryptographic mechanisms to identify and reject wireless transmissions that are deliberate attempts to achieve imitative or manipulative communications deception based on signal parameters.

Discussion

The implementation of cryptographic mechanisms to identify and reject imitative or manipulative communications ensures that the signal parameters of wireless transmissions are not predictable by unauthorized individuals. Such unpredictability reduces the probability of imitative or manipulative communications deception based on signal parameters alone.

NIST control statement

Implement cryptographic mechanisms to prevent the identification of [Assignment: wireless transmitters] by using the transmitter signal parameters.

Discussion

The implementation of cryptographic mechanisms to prevent the identification of wireless transmitters protects against the unique identification of wireless transmitters for the purposes of intelligence exploitation by ensuring that anti-fingerprinting alterations to signal parameters are not predictable by unauthorized individuals. It also provides anonymity when required. Radio fingerprinting techniques identify the unique signal parameters of transmitters to fingerprint such transmitters for purposes of tracking and mission or user identification.

NIST control statement

[Selection (one): physically; logically] disable or remove [Assignment: connection ports or input/output devices] on the following systems or system components: [Assignment: systems or system components].

Discussion

Connection ports include Universal Serial Bus (USB), Thunderbolt, and Firewire (IEEE 1394). Input/output (I/O) devices include compact disc and digital versatile disc drives. Disabling or removing such connection ports and I/O devices helps prevent the exfiltration of information from systems and the introduction of malicious code from those ports or devices. Physically disabling or removing ports and/or devices is the stronger action.

NIST control statement

a. Prohibit [Selection (one-or-more): the use of devices possessing [Assignment: environmental sensing capabilities] in [Assignment: facilities, areas, or systems] ; the remote activation of environmental sensing capabilities on organizational systems or system components with the following exceptions: [Assignment: exceptions where remote activation of sensors is allowed] ] ; and b. Provide an explicit indication of sensor use to [Assignment: group of users].

Discussion

Sensor capability and data applies to types of systems or system components characterized as mobile devices, such as cellular telephones, smart phones, and tablets. Mobile devices often include sensors that can collect and record data regarding the environment where the system is in use. Sensors that are embedded within mobile devices include microphones, cameras, Global Positioning System (GPS) mechanisms, and accelerometers. While the sensors on mobiles devices provide an important function, if activated covertly, such devices can potentially provide a means for adversaries to learn valuable information about individuals and organizations. For example, remotely activating the GPS function on a mobile device could provide an adversary with the ability to track the movements of an individual. Organizations may prohibit individuals from bringing cellular telephones or digital cameras into certain designated facilities or controlled areas within facilities where classified information is stored or sensitive conversations are taking place.

NIST control statement

Verify that the system is configured so that data or information collected by the [Assignment: sensors] is only reported to authorized individuals or roles.

Discussion

In situations where sensors are activated by authorized individuals, it is still possible that the data or information collected by the sensors will be sent to unauthorized entities.

NIST control statement

Employ the following measures so that data or information collected by [Unresolved source parameter: sc-42.01_odp] is only used for authorized purposes: [Assignment: measures].

Discussion

Information collected by sensors for a specific authorized purpose could be misused for some unauthorized purpose. For example, GPS sensors that are used to support traffic navigation could be misused to track the movements of individuals. Measures to mitigate such activities include additional training to help ensure that authorized individuals do not abuse their authority and, in the case where sensor data is maintained by external parties, contractual restrictions on the use of such data.

NIST control statement

Withdrawn in this source release; review the official source for disposition.

NIST control statement

Employ the following measures to facilitate an individual’s awareness that personally identifiable information is being collected by [Assignment: sensors]: [Assignment: measures].

Discussion

Awareness that organizational sensors are collecting data enables individuals to more effectively engage in managing their privacy. Measures can include conventional written notices and sensor configurations that make individuals directly or indirectly aware through other devices that the sensor is collecting information. The usability and efficacy of the notice are important considerations.

NIST control statement

Employ [Assignment: sensors] that are configured to minimize the collection of information about individuals that is not needed.

Discussion

Although policies to control for authorized use can be applied to information once it is collected, minimizing the collection of information that is not needed mitigates privacy risk at the system entry point and mitigates the risk of policy control failures. Sensor configurations include the obscuring of human features, such as blurring or pixelating flesh tones.

NIST control statement

a. Establish usage restrictions and implementation guidelines for the following system components: [Assignment: components] ; and b. Authorize, monitor, and control the use of such components within the system.

Discussion

Usage restrictions apply to all system components including but not limited to mobile code, mobile devices, wireless access, and wired and wireless peripheral components (e.g., copiers, printers, scanners, optical devices, and other similar technologies). The usage restrictions and implementation guidelines are based on the potential for system components to cause damage to the system and help to ensure that only authorized system use occurs.

NIST control statement

Employ a detonation chamber capability within [Assignment: system, system component, or location].

Discussion

Detonation chambers, also known as dynamic execution environments, allow organizations to open email attachments, execute untrusted or suspicious applications, and execute Universal Resource Locator requests in the safety of an isolated environment or a virtualized sandbox. Protected and isolated execution environments provide a means of determining whether the associated attachments or applications contain malicious code. While related to the concept of deception nets, the employment of detonation chambers is not intended to maintain a long-term environment in which adversaries can operate and their actions can be observed. Rather, detonation chambers are intended to quickly identify malicious code and either reduce the likelihood that the code is propagated to user environments of operation or prevent such propagation completely.

NIST control statement

Synchronize system clocks within and between systems and system components.

Discussion

Time synchronization of system clocks is essential for the correct execution of many system services, including identification and authentication processes that involve certificates and time-of-day restrictions as part of access control. Denial of service or failure to deny expired credentials may result without properly synchronized clocks within and between systems and system components. Time is commonly expressed in Coordinated Universal Time (UTC), a modern continuation of Greenwich Mean Time (GMT), or local time with an offset from UTC. The granularity of time measurements refers to the degree of synchronization between system clocks and reference clocks, such as clocks synchronizing within hundreds of milliseconds or tens of milliseconds. Organizations may define different time granularities for system components. Time service can be critical to other security capabilities—such as access control and identification and authentication—depending on the nature of the mechanisms used to support the capabilities.

NIST control statement

(a) Compare the internal system clocks [Assignment: frequency] with [Assignment: authoritative time source] ; and (b) Synchronize the internal system clocks to the authoritative time source when the time difference is greater than [Assignment: time period].

Discussion

Synchronization of internal system clocks with an authoritative source provides uniformity of time stamps for systems with multiple system clocks and systems connected over a network.

NIST control statement

(a) Identify a secondary authoritative time source that is in a different geographic region than the primary authoritative time source; and (b) Synchronize the internal system clocks to the secondary authoritative time source if the primary authoritative time source is unavailable.

Discussion

It may be necessary to employ geolocation information to determine that the secondary authoritative time source is in a different geographic region.

NIST control statement

Implement a policy enforcement mechanism [Selection (one): physically; logically] between the physical and/or network interfaces for the connecting security domains.

Discussion

For logical policy enforcement mechanisms, organizations avoid creating a logical path between interfaces to prevent the ability to bypass the policy enforcement mechanism. For physical policy enforcement mechanisms, the robustness of physical isolation afforded by the physical implementation of policy enforcement to preclude the presence of logical covert channels penetrating the security domain may be needed. Contact [ncdsmo@nsa.gov](mailto:ncdsmo@nsa.gov) for more information.

NIST control statement

Establish [Assignment: alternate communication paths] for system operations organizational command and control.

Discussion

An incident, whether adversarial- or nonadversarial-based, can disrupt established communications paths used for system operations and organizational command and control. Alternate communications paths reduce the risk of all communications paths being affected by the same incident. To compound the problem, the inability of organizational officials to obtain timely information about disruptions or to provide timely direction to operational elements after a communications path incident, can impact the ability of the organization to respond to such incidents in a timely manner. Establishing alternate communications paths for command and control purposes, including designating alternative decision makers if primary decision makers are unavailable and establishing the extent and limitations of their actions, can greatly facilitate the organization’s ability to continue to operate and take appropriate actions during an incident.