📖 Electronic (OSCAL) Version of NIST SP 800-53 Rev 5.2.0 Controls and SP 800-53A Rev 5.2.0 Assessment Procedures

Access control policy and procedures address the controls in the AC family that are implemented within systems and organizations. The risk management strategy is an important factor in establishing such policies and procedures. Policies and procedures contribute to security and privacy assurance. Therefore, it is important that security and privacy programs collaborate on the development of access control policy and procedures. Security and privacy program policies and procedures at the organization level are preferable, in general, and may obviate the need for mission- or system-specific policies and procedures. The policy can be included as part of the general security and privacy policy or be represented by multiple policies reflecting the complex nature of organizations. Procedures can be established for security and privacy programs, for mission or business processes, and for systems, if needed. Procedures describe how the policies or controls are implemented and can be directed at the individual or role that is the object of the procedure. Procedures can be documented in system security and privacy plans or in one or more separate documents. Events that may precipitate an update to access control policy and procedures include assessment or audit findings, security incidents or breaches, or changes in laws, executive orders, directives, regulations, policies, standards, and guidelines. Simply restating controls does not constitute an organizational policy or procedure.

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.

Enforce approved authorizations for logical access to information and system resources in accordance with applicable access control policies.

Access control policies control access between active entities or subjects (i.e., users or processes acting on behalf of users) and passive entities or objects (i.e., devices, files, records, domains) in organizational systems. In addition to enforcing authorized access at the system level and recognizing that systems can host many applications and services in support of mission and business functions, access enforcement mechanisms can also be employed at the application and service level to provide increased information security and privacy. In contrast to logical access controls that are implemented within the system, physical access controls are addressed by the controls in the Physical and Environmental Protection ( [PE](#pe) ) family.

approved authorizations for logical access to information and system resources are enforced in accordance with applicable access control policies.

Enforce approved authorizations for controlling the flow of information within the system and between connected systems based on {{ insert: param, ac-04_odp }}.

Information flow control regulates where information can travel within a system and between systems (in contrast to who is allowed to access the information) and without regard to subsequent accesses to that information. Flow control restrictions include blocking external traffic that claims to be from within the organization, keeping export-controlled information from being transmitted in the clear to the Internet, restricting web requests that are not from the internal web proxy server, and limiting information transfers between organizations based on data structures and content. Transferring information between organizations may require an agreement specifying how the information flow is enforced (see [CA-3](#ca-3) ). Transferring information between systems in different security or privacy domains with different security or privacy policies introduces the risk that such transfers violate one or more domain security or privacy policies. In such situations, information owners/stewards provide guidance at designated policy enforcement points between connected systems. Organizations consider mandating specific architectural solutions to enforce specific security and privacy policies. Enforcement includes prohibiting information transfers between connected systems (i.e., allowing access only), verifying write permissions before accepting information from another security or privacy domain or connected system, employing hardware mechanisms to enforce one-way information flows, and implementing trustworthy regrading mechanisms to reassign security or privacy attributes and labels. Organizations commonly employ information flow control policies and enforcement mechanisms to control the flow of information between designated sources and destinations within systems and between connected systems. Flow control is based on the characteristics of the information and/or the information path. Enforcement occurs, for example, in boundary protection devices that employ rule sets or establish configuration settings that restrict system services, provide a packet-filtering capability based on header information, or provide a message-filtering capability based on message content. Organizations also consider the trustworthiness of filtering and/or inspection mechanisms (i.e., hardware, firmware, and software components) that are critical to information flow enforcement. Control enhancements 3 through 32 primarily address cross-domain solution needs that focus on more advanced filtering techniques, in-depth analysis, and stronger flow enforcement mechanisms implemented in cross-domain products, such as high-assurance guards. Such capabilities are generally not available in commercial off-the-shelf products. Information flow enforcement also applies to control plane traffic (e.g., routing and DNS).

approved authorizations are enforced for controlling the flow of information within the system and between connected systems based on {{ insert: param, ac-04_odp }}.

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).

Employ the principle of least privilege, allowing only authorized accesses for users (or processes acting on behalf of users) that are necessary to accomplish assigned organizational tasks.

Organizations employ least privilege for specific duties and systems. The principle of least privilege is also applied to system processes, ensuring that the processes have access to systems and operate at privilege levels no higher than necessary to accomplish organizational missions or business functions. Organizations consider the creation of additional processes, roles, and accounts as necessary to achieve least privilege. Organizations apply least privilege to the development, implementation, and operation of organizational systems.

the principle of least privilege is employed, allowing only authorized accesses for users (or processes acting on behalf of users) that are necessary to accomplish assigned organizational tasks.

The need to limit unsuccessful logon attempts and take subsequent action when the maximum number of attempts is exceeded applies regardless of whether the logon occurs via a local or network connection. Due to the potential for denial of service, automatic lockouts initiated by systems are usually temporary and automatically release after a predetermined, organization-defined time period. If a delay algorithm is selected, organizations may employ different algorithms for different components of the system based on the capabilities of those components. Responses to unsuccessful logon attempts may be implemented at the operating system and the application levels. Organization-defined actions that may be taken when the number of allowed consecutive invalid logon attempts is exceeded include prompting the user to answer a secret question in addition to the username and password, invoking a lockdown mode with limited user capabilities (instead of full lockout), allowing users to only logon from specified Internet Protocol (IP) addresses, requiring a CAPTCHA to prevent automated attacks, or applying user profiles such as location, time of day, IP address, device, or Media Access Control (MAC) address. If automatic system lockout or execution of a delay algorithm is not implemented in support of the availability objective, organizations consider a combination of other actions to help prevent brute force attacks. In addition to the above, organizations can prompt users to respond to a secret question before the number of allowed unsuccessful logon attempts is exceeded. Automatically unlocking an account after a specified period of time is generally not permitted. However, exceptions may be required based on operational mission or need.

System use notifications can be implemented using messages or warning banners displayed before individuals log in to systems. System use notifications are used only for access via logon interfaces with human users. Notifications are not required when human interfaces do not exist. Based on an assessment of risk, organizations consider whether or not a secondary system use notification is needed to access applications or other system resources after the initial network logon. Organizations consider system use notification messages or banners displayed in multiple languages based on organizational needs and the demographics of system users. Organizations consult with the privacy office for input regarding privacy messaging and the Office of the General Counsel or organizational equivalent for legal review and approval of warning banner content.

Notify the user, upon successful logon to the system, of the date and time of the last logon.

Previous logon notification is applicable to system access via human user interfaces and access to systems that occurs in other types of architectures. Information about the last successful logon allows the user to recognize if the date and time provided is not consistent with the user’s last access.

the user is notified, upon successful logon to the system, of the date and time of the last logon.

Limit the number of concurrent sessions for each {{ insert: param, ac-10_odp.01 }} to {{ insert: param, ac-10_odp.02 }}.

Organizations may define the maximum number of concurrent sessions for system accounts globally, by account type, by account, or any combination thereof. For example, organizations may limit the number of concurrent sessions for system administrators or other individuals working in particularly sensitive domains or mission-critical applications. Concurrent session control addresses concurrent sessions for system accounts. It does not, however, address concurrent sessions by single users via multiple system accounts.

the number of concurrent sessions for each {{ insert: param, ac-10_odp.01 }} is limited to {{ insert: param, ac-10_odp.02 }}.

Device locks are temporary actions taken to prevent logical access to organizational systems when users stop work and move away from the immediate vicinity of those systems but do not want to log out because of the temporary nature of their absences. Device locks can be implemented at the operating system level or at the application level. A proximity lock may be used to initiate the device lock (e.g., via a Bluetooth-enabled device or dongle). User-initiated device locking is behavior or policy-based and, as such, requires users to take physical action to initiate the device lock. Device locks are not an acceptable substitute for logging out of systems, such as when organizations require users to log out at the end of workdays.

Automatically terminate a user session after {{ insert: param, ac-12_odp }}.

Session termination addresses the termination of user-initiated logical sessions (in contrast to [SC-10](#sc-10) , which addresses the termination of network connections associated with communications sessions (i.e., network disconnect)). A logical session (for local, network, and remote access) is initiated whenever a user (or process acting on behalf of a user) accesses an organizational system. Such user sessions can be terminated without terminating network sessions. Session termination ends all processes associated with a user’s logical session except for those processes that are specifically created by the user (i.e., session owner) to continue after the session is terminated. Conditions or trigger events that require automatic termination of the session include organization-defined periods of user inactivity, targeted responses to certain types of incidents, or time-of-day restrictions on system use.

a user session is automatically terminated after {{ insert: param, ac-12_odp }}.

Specific user actions may be permitted without identification or authentication if organizations determine that identification and authentication are not required for the specified user actions. Organizations may allow a limited number of user actions without identification or authentication, including when individuals access public websites or other publicly accessible federal systems, when individuals use mobile phones to receive calls, or when facsimiles are received. Organizations identify actions that normally require identification or authentication but may, under certain circumstances, allow identification or authentication mechanisms to be bypassed. Such bypasses may occur, for example, via a software-readable physical switch that commands bypass of the logon functionality and is protected from accidental or unmonitored use. Permitting actions without identification or authentication does not apply to situations where identification and authentication have already occurred and are not repeated but rather to situations where identification and authentication have not yet occurred. Organizations may decide that there are no user actions that can be performed on organizational systems without identification and authentication, and therefore, the value for the assignment operation can be "none."

Information is represented internally within systems using abstractions known as data structures. Internal data structures can represent different types of entities, both active and passive. Active entities, also known as subjects, are typically associated with individuals, devices, or processes acting on behalf of individuals. Passive entities, also known as objects, are typically associated with data structures, such as records, buffers, tables, files, inter-process pipes, and communications ports. Security attributes, a form of metadata, are abstractions that represent the basic properties or characteristics of active and passive entities with respect to safeguarding information. Privacy attributes, which may be used independently or in conjunction with security attributes, represent the basic properties or characteristics of active or passive entities with respect to the management of personally identifiable information. Attributes can be either explicitly or implicitly associated with the information contained in organizational systems or system components. Attributes may be associated with active entities (i.e., subjects) that have the potential to send or receive information, cause information to flow among objects, or change the system state. These attributes may also be associated with passive entities (i.e., objects) that contain or receive information. The association of attributes to subjects and objects by a system is referred to as binding and is inclusive of setting the attribute value and the attribute type. Attributes, when bound to data or information, permit the enforcement of security and privacy policies for access control and information flow control, including data retention limits, permitted uses of personally identifiable information, and identification of personal information within data objects. Such enforcement occurs through organizational processes or system functions or mechanisms. The binding techniques implemented by systems affect the strength of attribute binding to information. Binding strength and the assurance associated with binding techniques play important parts in the trust that organizations have in the information flow enforcement process. The binding techniques affect the number and degree of additional reviews required by organizations. The content or assigned values of attributes can directly affect the ability of individuals to access organizational information. Organizations can define the types of attributes needed for systems to support missions or business functions. There are many values that can be assigned to a security attribute. By specifying the permitted attribute ranges and values, organizations ensure that attribute values are meaningful and relevant. Labeling refers to the association of attributes with the subjects and objects represented by the internal data structures within systems. This facilitates system-based enforcement of information security and privacy policies. Labels include classification of information in accordance with legal and compliance requirements (e.g., top secret, secret, confidential, controlled unclassified), information impact level; high value asset information, access authorizations, nationality; data life cycle protection (i.e., encryption and data expiration), personally identifiable information processing permissions, including individual consent to personally identifiable information processing, and contractor affiliation. A related term to labeling is marking. Marking refers to the association of attributes with objects in a human-readable form and displayed on system media. Marking enables manual, procedural, or process-based enforcement of information security and privacy policies. Security and privacy labels may have the same value as media markings (e.g., top secret, secret, confidential). See [MP-3](#mp-3) (Media Marking).