NIST SP 800-53 Rev. 5 Common Control Library

NIST control statement

a. Define and document the types of accounts allowed and specifically prohibited for use within the system; b. Assign account managers; c. Require [Assignment: prerequisites and criteria] for group and role membership; d. Specify: 1. Authorized users of the system; 2. Group and role membership; and 3. Access authorizations (i.e., privileges) and [Assignment: attributes (as required)] for each account; e. Require approvals by [Assignment: personnel or roles] for requests to create accounts; f. Create, enable, modify, disable, and remove accounts in accordance with [Assignment: policy, procedures, prerequisites, and criteria]; g. Monitor the use of accounts; h. Notify account managers and [Assignment: personnel or roles] within: 1. [Assignment: time period] when accounts are no longer required; 2. [Assignment: time period] when users are terminated or transferred; and 3. [Assignment: time period] when system usage or need-to-know changes for an individual; i. Authorize access to the system based on: 1. A valid access authorization; 2. Intended system usage; and 3. [Assignment: attributes (as required)]; j. Review accounts for compliance with account management requirements [Assignment: frequency]; k. Establish and implement a process for changing shared or group account authenticators (if deployed) when individuals are removed from the group; and l. Align account management processes with personnel termination and transfer processes.

Discussion

Examples of system account types include individual, shared, group, system, guest, anonymous, emergency, developer, temporary, and service. Identification of authorized system users and the specification of access privileges reflect the requirements in other controls in the security plan. Users requiring administrative privileges on system accounts receive additional scrutiny by organizational personnel responsible for approving such accounts and privileged access, including system owner, mission or business owner, senior agency information security officer, or senior agency official for privacy. Types of accounts that organizations may wish to prohibit due to increased risk include shared, group, emergency, anonymous, temporary, and guest accounts. Where access involves personally identifiable information, security programs collaborate with the senior agency official for privacy to establish the specific conditions for group and role membership; specify authorized users, group and role membership, and access authorizations for each account; and create, adjust, or remove system accounts in accordance with organizational policies. Policies can include such information as account expiration dates or other factors that trigger the disabling of accounts. Organizations may choose to define access privileges or other attributes by account, type of account, or a combination of the two. Examples of other attributes required for authorizing access include restrictions on time of day, day of week, and point of origin. In defining other system account attributes, organizations consider system-related requirements and mission/business requirements. Failure to consider these factors could affect system availability. Temporary and emergency accounts are intended for short-term use. Organizations establish temporary accounts as part of normal account activation procedures when there is a need for short-term accounts without the demand for immediacy in account activation. Organizations establish emergency accounts in response to crisis situations and with the need for rapid account activation. Therefore, emergency account activation may bypass normal account authorization processes. Emergency and temporary accounts are not to be confused with infrequently used accounts, including local logon accounts used for special tasks or when network resources are unavailable (may also be known as accounts of last resort). Such accounts remain available and are not subject to automatic disabling or removal dates. Conditions for disabling or deactivating accounts include when shared/group, emergency, or temporary accounts are no longer required and when individuals are transferred or terminated. Changing shared/group authenticators when members leave the group is intended to ensure that former group members do not retain access to the shared or group account. Some types of system accounts may require specialized training.

NIST control statement

Support the management of system accounts using [Assignment: automated mechanisms].

Discussion

Automated system account management includes using automated mechanisms to create, enable, modify, disable, and remove accounts; notify account managers when an account is created, enabled, modified, disabled, or removed, or when users are terminated or transferred; monitor system account usage; and report atypical system account usage. Automated mechanisms can include internal system functions and email, telephonic, and text messaging notifications.

NIST control statement

Automatically [Selection (one): remove; disable] temporary and emergency accounts after [Assignment: time period].

Discussion

Management of temporary and emergency accounts includes the removal or disabling of such accounts automatically after a predefined time period rather than at the convenience of the system administrator. Automatic removal or disabling of accounts provides a more consistent implementation.

NIST control statement

Disable accounts within [Assignment: time period] when the accounts: (a) Have expired; (b) Are no longer associated with a user or individual; (c) Are in violation of organizational policy; or (d) Have been inactive for [Assignment: time period].

Discussion

Disabling expired, inactive, or otherwise anomalous accounts supports the concepts of least privilege and least functionality which reduce the attack surface of the system.

NIST control statement

Automatically audit account creation, modification, enabling, disabling, and removal actions.

Discussion

Account management audit records are defined in accordance with [AU-02](#au-2) and reviewed, analyzed, and reported in accordance with [AU-06](#au-6).

NIST control statement

Require that users log out when [Assignment: time period of expected inactivity or description of when to log out].

Discussion

Inactivity logout is behavior- or policy-based and requires users to take physical action to log out when they are expecting inactivity longer than the defined period. Automatic enforcement of inactivity logout is addressed by [AC-11](#ac-11).

NIST control statement

Implement [Assignment: dynamic privilege management capabilities].

Discussion

In contrast to access control approaches that employ static accounts and predefined user privileges, dynamic access control approaches rely on runtime access control decisions facilitated by dynamic privilege management, such as attribute-based access control. While user identities remain relatively constant over time, user privileges typically change more frequently based on ongoing mission or business requirements and the operational needs of organizations. An example of dynamic privilege management is the immediate revocation of privileges from users as opposed to requiring that users terminate and restart their sessions to reflect changes in privileges. Dynamic privilege management can also include mechanisms that change user privileges based on dynamic rules as opposed to editing specific user profiles. Examples include automatic adjustments of user privileges if they are operating out of their normal work times, if their job function or assignment changes, or if systems are under duress or in emergency situations. Dynamic privilege management includes the effects of privilege changes, for example, when there are changes to encryption keys used for communications.

NIST control statement

(a) Establish and administer privileged user accounts in accordance with [Selection (one): a role-based access scheme; an attribute-based access scheme]; (b) Monitor privileged role or attribute assignments; (c) Monitor changes to roles or attributes; and (d) Revoke access when privileged role or attribute assignments are no longer appropriate.

Discussion

Privileged roles are organization-defined roles assigned to individuals that allow those individuals to perform certain security-relevant functions that ordinary users are not authorized to perform. Privileged roles include key management, account management, database administration, system and network administration, and web administration. A role-based access scheme organizes permitted system access and privileges into roles. In contrast, an attribute-based access scheme specifies allowed system access and privileges based on attributes.

NIST control statement

Create, activate, manage, and deactivate [Assignment: system accounts] dynamically.

Discussion

Approaches for dynamically creating, activating, managing, and deactivating system accounts rely on automatically provisioning the accounts at runtime for entities that were previously unknown. Organizations plan for the dynamic management, creation, activation, and deactivation of system accounts by establishing trust relationships, business rules, and mechanisms with appropriate authorities to validate related authorizations and privileges.

NIST control statement

Only permit the use of shared and group accounts that meet [Assignment: conditions].

Discussion

Before permitting the use of shared or group accounts, organizations consider the increased risk due to the lack of accountability with such accounts.

NIST control statement

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

NIST control statement

Enforce [Assignment: circumstances and/or usage conditions] for [Assignment: system accounts].

Discussion

Specifying and enforcing usage conditions helps to enforce the principle of least privilege, increase user accountability, and enable effective account monitoring. Account monitoring includes alerts generated if the account is used in violation of organizational parameters. Organizations can describe specific conditions or circumstances under which system accounts can be used, such as by restricting usage to certain days of the week, time of day, or specific durations of time.

NIST control statement

(a) Monitor system accounts for [Assignment: atypical usage] ; and (b) Report atypical usage of system accounts to [Assignment: personnel or roles].

Discussion

Atypical usage includes accessing systems at certain times of the day or from locations that are not consistent with the normal usage patterns of individuals. Monitoring for atypical usage may reveal rogue behavior by individuals or an attack in progress. Account monitoring may inadvertently create privacy risks since data collected to identify atypical usage may reveal previously unknown information about the behavior of individuals. Organizations assess and document privacy risks from monitoring accounts for atypical usage in their privacy impact assessment and make determinations that are in alignment with their privacy program plan.

NIST control statement

Disable accounts of individuals within [Assignment: time period] of discovery of [Assignment: significant risks].

Discussion

Users who pose a significant security and/or privacy risk include individuals for whom reliable evidence indicates either the intention to use authorized access to systems to cause harm or through whom adversaries will cause harm. Such harm includes adverse impacts to organizational operations, organizational assets, individuals, other organizations, or the Nation. Close coordination among system administrators, legal staff, human resource managers, and authorizing officials is essential when disabling system accounts for high-risk individuals.

NIST control statement

Enforce [Assignment: organization-defined mandatory access control policy] over the set of covered subjects and objects specified in the policy, and where the policy: (a) Is uniformly enforced across the covered subjects and objects within the system; (b) Specifies that a subject that has been granted access to information is constrained from doing any of the following; (1) Passing the information to unauthorized subjects or objects; (2) Granting its privileges to other subjects; (3) Changing one or more security attributes (specified by the policy) on subjects, objects, the system, or system components; (4) Choosing the security attributes and attribute values (specified by the policy) to be associated with newly created or modified objects; and (5) Changing the rules governing access control; and (c) Specifies that [Assignment: subjects] may explicitly be granted [Assignment: privileges] such that they are not limited by any defined subset (or all) of the above constraints.

Discussion

Mandatory access control is a type of nondiscretionary access control. Mandatory access control policies constrain what actions subjects can take with information obtained from objects for which they have already been granted access. This prevents the subjects from passing the information to unauthorized subjects and objects. Mandatory access control policies constrain actions that subjects can take with respect to the propagation of access control privileges; that is, a subject with a privilege cannot pass that privilege to other subjects. The policy is uniformly enforced over all subjects and objects to which the system has control. Otherwise, the access control policy can be circumvented. This enforcement is provided by an implementation that meets the reference monitor concept as described in [AC-25](#ac-25) . The policy is bounded by the system (i.e., once the information is passed outside of the control of the system, additional means may be required to ensure that the constraints on the information remain in effect). The trusted subjects described above are granted privileges consistent with the concept of least privilege (see [AC-6](#ac-6) ). Trusted subjects are only given the minimum privileges necessary for satisfying organizational mission/business needs relative to the above policy. The control is most applicable when there is a mandate that establishes a policy regarding access to controlled unclassified information or classified information and some users of the system are not authorized access to all such information resident in the system. Mandatory access control can operate in conjunction with discretionary access control as described in [AC-3(4)](#ac-3.4) . A subject constrained in its operation by mandatory access control policies can still operate under the less rigorous constraints of AC-3(4), but mandatory access control policies take precedence over the less rigorous constraints of AC-3(4). For example, while a mandatory access control policy imposes a constraint that prevents a subject from passing information to another subject operating at a different impact or classification level, AC-3(4) permits the subject to pass the information to any other subject with the same impact or classification level as the subject. Examples of mandatory access control policies include the Bell-LaPadula policy to protect confidentiality of information and the Biba policy to protect the integrity of information.

NIST control statement

a. Identify and document [Assignment: duties of individuals] ; and b. Define system access authorizations to support separation of duties.

Discussion

Separation of duties addresses the potential for abuse of authorized privileges and helps to reduce the risk of malevolent activity without collusion. Separation of duties includes dividing mission or business functions and support functions among different individuals or roles, conducting system support functions with different individuals, and ensuring that security personnel who administer access control functions do not also administer audit functions. Because separation of duty violations can span systems and application domains, organizations consider the entirety of systems and system components when developing policy on separation of duties. Separation of duties is enforced through the account management activities in [AC-2](#ac-2) , access control mechanisms in [AC-3](#ac-3) , and identity management activities in [IA-2](#ia-2), [IA-4](#ia-4) , and [IA-12](#ia-12).

NIST control statement

a. Establish configuration requirements, connection requirements, and implementation guidance for organization-controlled mobile devices, to include when such devices are outside of controlled areas; and b. Authorize the connection of mobile devices to organizational systems.

Discussion

A mobile device is a computing device that has a small form factor such that it can easily be carried by a single individual; is designed to operate without a physical connection; possesses local, non-removable or removable data storage; and includes a self-contained power source. Mobile device functionality may also include voice communication capabilities, on-board sensors that allow the device to capture information, and/or built-in features for synchronizing local data with remote locations. Examples include smart phones and tablets. Mobile devices are typically associated with a single individual. The processing, storage, and transmission capability of the mobile device may be comparable to or merely a subset of notebook/desktop systems, depending on the nature and intended purpose of the device. Protection and control of mobile devices is behavior or policy-based and requires users to take physical action to protect and control such devices when outside of controlled areas. Controlled areas are spaces for which organizations provide physical or procedural controls to meet the requirements established for protecting information and systems. Due to the large variety of mobile devices with different characteristics and capabilities, organizational restrictions may vary for the different classes or types of such devices. Usage restrictions and specific implementation guidance for mobile devices include configuration management, device identification and authentication, implementation of mandatory protective software, scanning devices for malicious code, updating virus protection software, scanning for critical software updates and patches, conducting primary operating system (and possibly other resident software) integrity checks, and disabling unnecessary hardware. Usage restrictions and authorization to connect may vary among organizational systems. For example, the organization may authorize the connection of mobile devices to its network and impose a set of usage restrictions, while a system owner may withhold authorization for mobile device connection to specific applications or impose additional usage restrictions before allowing mobile device connections to a system. Adequate security for mobile devices goes beyond the requirements specified in [AC-19](#ac-19) . Many safeguards for mobile devices are reflected in other controls. [AC-20](#ac-20) addresses mobile devices that are not organization-controlled.

NIST control statement

a. [Selection (one-or-more): establish [Assignment: terms and conditions] ; identify [Assignment: controls asserted] ] , consistent with the trust relationships established with other organizations owning, operating, and/or maintaining external systems, allowing authorized individuals to: 1. Access the system from external systems; and 2. Process, store, or transmit organization-controlled information using external systems; or b. Prohibit the use of [Assignment: prohibited types of external systems].

Discussion

External systems are systems that are used by but not part of organizational systems, and for which the organization has no direct control over the implementation of required controls or the assessment of control effectiveness. External systems include personally owned systems, components, or devices; privately owned computing and communications devices in commercial or public facilities; systems owned or controlled by nonfederal organizations; systems managed by contractors; and federal information systems that are not owned by, operated by, or under the direct supervision or authority of the organization. External systems also include systems owned or operated by other components within the same organization and systems within the organization with different authorization boundaries. Organizations have the option to prohibit the use of any type of external system or prohibit the use of specified types of external systems, (e.g., prohibit the use of any external system that is not organizationally owned or prohibit the use of personally-owned systems). For some external systems (i.e., systems operated by other organizations), the trust relationships that have been established between those organizations and the originating organization may be such that no explicit terms and conditions are required. Systems within these organizations may not be considered external. These situations occur when, for example, there are pre-existing information exchange agreements (either implicit or explicit) established between organizations or components or when such agreements are specified by applicable laws, executive orders, directives, regulations, policies, or standards. Authorized individuals include organizational personnel, contractors, or other individuals with authorized access to organizational systems and over which organizations have the authority to impose specific rules of behavior regarding system access. Restrictions that organizations impose on authorized individuals need not be uniform, as the restrictions may vary depending on trust relationships between organizations. Therefore, organizations may choose to impose different security restrictions on contractors than on state, local, or tribal governments. External systems used to access public interfaces to organizational systems are outside the scope of [AC-20](#ac-20) . Organizations establish specific terms and conditions for the use of external systems in accordance with organizational security policies and procedures. At a minimum, terms and conditions address the specific types of applications that can be accessed on organizational systems from external systems and the highest security category of information that can be processed, stored, or transmitted on external systems. If the terms and conditions with the owners of the external systems cannot be established, organizations may impose restrictions on organizational personnel using those external systems.

NIST control statement

Permit authorized individuals to use an external system to access the system or to process, store, or transmit organization-controlled information only after: (a) Verification of the implementation of controls on the external system as specified in the organization’s security and privacy policies and security and privacy plans; or (b) Retention of approved system connection or processing agreements with the organizational entity hosting the external system.

Discussion

Limiting authorized use recognizes circumstances where individuals using external systems may need to access organizational systems. Organizations need assurance that the external systems contain the necessary controls so as not to compromise, damage, or otherwise harm organizational systems. Verification that the required controls have been implemented can be achieved by external, independent assessments, attestations, or other means, depending on the confidence level required by organizations.

NIST control statement

Restrict the use of organization-controlled portable storage devices by authorized individuals on external systems using [Assignment: restrictions].

Discussion

Limits on the use of organization-controlled portable storage devices in external systems include restrictions on how the devices may be used and under what conditions the devices may be used.

NIST control statement

Restrict the use of non-organizationally owned systems or system components to process, store, or transmit organizational information using [Assignment: restrictions].

Discussion

Non-organizationally owned systems or system components include systems or system components owned by other organizations as well as personally owned devices. There are potential risks to using non-organizationally owned systems or components. In some cases, the risk is sufficiently high as to prohibit such use (see [AC-20 b.](#ac-20_smt.b) ). In other cases, the use of such systems or system components may be allowed but restricted in some way. Restrictions include requiring the implementation of approved controls prior to authorizing the connection of non-organizationally owned systems and components; limiting access to types of information, services, or applications; using virtualization techniques to limit processing and storage activities to servers or system components provisioned by the organization; and agreeing to the terms and conditions for usage. Organizations consult with the Office of the General Counsel regarding legal issues associated with using personally owned devices, including requirements for conducting forensic analyses during investigations after an incident.

NIST control statement

Prohibit the use of [Assignment: network-accessible storage devices] in external systems.

Discussion

Network-accessible storage devices in external systems include online storage devices in public, hybrid, or community cloud-based systems.

NIST control statement

Prohibit the use of organization-controlled portable storage devices by authorized individuals on external systems.

Discussion

Limits on the use of organization-controlled portable storage devices in external systems include a complete prohibition of the use of such devices. Prohibiting such use is enforced using technical methods and/or nontechnical (i.e., process-based) methods.

NIST control statement

a. Enable authorized users to determine whether access authorizations assigned to a sharing partner match the information’s access and use restrictions for [Assignment: information-sharing circumstances] ; and b. Employ [Assignment: automated mechanisms] to assist users in making information sharing and collaboration decisions.

Discussion

Information sharing applies to information that may be restricted in some manner based on some formal or administrative determination. Examples of such information include, contract-sensitive information, classified information related to special access programs or compartments, privileged information, proprietary information, and personally identifiable information. Security and privacy risk assessments as well as applicable laws, regulations, and policies can provide useful inputs to these determinations. Depending on the circumstances, sharing partners may be defined at the individual, group, or organizational level. Information may be defined by content, type, security category, or special access program or compartment. Access restrictions may include non-disclosure agreements (NDA). Information flow techniques and security attributes may be used to provide automated assistance to users making sharing and collaboration decisions.

NIST control statement

Employ [Assignment: automated mechanisms] to enforce information-sharing decisions by authorized users based on access authorizations of sharing partners and access restrictions on information to be shared.

Discussion

Automated mechanisms are used to enforce information sharing decisions.