NIST SP 800-53 Rev. 5 Common Control Library

NIST control statement

Enforce approved authorizations for controlling the flow of information within the system and between connected systems based on [Assignment: information flow control policies].

Discussion

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).

NIST control statement

a. Establish and document usage restrictions, configuration/connection requirements, and implementation guidance for each type of remote access allowed; and b. Authorize each type of remote access to the system prior to allowing such connections.

Discussion

Remote access is access to organizational systems (or processes acting on behalf of users) that communicate through external networks such as the Internet. Types of remote access include dial-up, broadband, and wireless. Organizations use encrypted virtual private networks (VPNs) to enhance confidentiality and integrity for remote connections. The use of encrypted VPNs provides sufficient assurance to the organization that it can effectively treat such connections as internal networks if the cryptographic mechanisms used are implemented in accordance with applicable laws, executive orders, directives, regulations, policies, standards, and guidelines. Still, VPN connections traverse external networks, and the encrypted VPN does not enhance the availability of remote connections. VPNs with encrypted tunnels can also affect the ability to adequately monitor network communications traffic for malicious code. Remote access controls apply to systems other than public web servers or systems designed for public access. Authorization of each remote access type addresses authorization prior to allowing remote access without specifying the specific formats for such authorization. While organizations may use information exchange and system connection security agreements to manage remote access connections to other systems, such agreements are addressed as part of [CA-3](#ca-3) . Enforcing access restrictions for remote access is addressed via [AC-3](#ac-3).

NIST control statement

a. Approve and manage the exchange of information between the system and other systems using [Selection (one-or-more): interconnection security agreements; information exchange security agreements; memoranda of understanding or agreement; service level agreements; user agreements; non-disclosure agreements; [Assignment: type of agreement] ]; b. Document, as part of each exchange agreement, the interface characteristics, security and privacy requirements, controls, and responsibilities for each system, and the impact level of the information communicated; and c. Review and update the agreements [Assignment: frequency].

Discussion

System information exchange requirements apply to information exchanges between two or more systems. System information exchanges include connections via leased lines or virtual private networks, connections to internet service providers, database sharing or exchanges of database transaction information, connections and exchanges with cloud services, exchanges via web-based services, or exchanges of files via file transfer protocols, network protocols (e.g., IPv4, IPv6), email, or other organization-to-organization communications. Organizations consider the risk related to new or increased threats that may be introduced when systems exchange information with other systems that may have different security and privacy requirements and controls. This includes systems within the same organization and systems that are external to the organization. A joint authorization of the systems exchanging information, as described in [CA-6(1)](#ca-6.1) or [CA-6(2)](#ca-6.2) , may help to communicate and reduce risk. Authorizing officials determine the risk associated with system information exchange and the controls needed for appropriate risk mitigation. The types of agreements selected are based on factors such as the impact level of the information being exchanged, the relationship between the organizations exchanging information (e.g., government to government, government to business, business to business, government or business to service provider, government or business to individual), or the level of access to the organizational system by users of the other system. If systems that exchange information have the same authorizing official, organizations need not develop agreements. Instead, the interface characteristics between the systems (e.g., how the information is being exchanged. how the information is protected) are described in the respective security and privacy plans. If the systems that exchange information have different authorizing officials within the same organization, the organizations can develop agreements or provide the same information that would be provided in the appropriate agreement type from [CA-3a](#ca-3_smt.a) in the respective security and privacy plans for the systems. Organizations may incorporate agreement information into formal contracts, especially for information exchanges established between federal agencies and nonfederal organizations (including service providers, contractors, system developers, and system integrators). Risk considerations include systems that share the same networks.

NIST control statement

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

NIST control statement

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

NIST control statement

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

NIST control statement

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

NIST control statement

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

NIST control statement

Verify that individuals or systems transferring data between interconnecting systems have the requisite authorizations (i.e., write permissions or privileges) prior to accepting such data.

Discussion

To prevent unauthorized individuals and systems from making information transfers to protected systems, the protected system verifies—via independent means— whether the individual or system attempting to transfer information is authorized to do so. Verification of the authorization to transfer information also applies to control plane traffic (e.g., routing and DNS) and services (e.g., authenticated SMTP relays).

NIST control statement

(a) Identify transitive (downstream) information exchanges with other systems through the systems identified in [CA-3a](#ca-3_smt.a) ; and (b) Take measures to ensure that transitive (downstream) information exchanges cease when the controls on identified transitive (downstream) systems cannot be verified or validated.

Discussion

Transitive or "downstream" information exchanges are information exchanges between the system or systems with which the organizational system exchanges information and other systems. For mission-essential systems, services, and applications, including high value assets, it is necessary to identify such information exchanges. The transparency of the controls or protection measures in place in such downstream systems connected directly or indirectly to organizational systems is essential to understanding the security and privacy risks resulting from those information exchanges. Organizational systems can inherit risk from downstream systems through transitive connections and information exchanges, which can make the organizational systems more susceptible to threats, hazards, and adverse impacts.

NIST control statement

(a) Identify [Assignment: software programs]; (b) Employ a deny-all, permit-by-exception policy to allow the execution of authorized software programs on the system; and (c) Review and update the list of authorized software programs [Assignment: frequency].

Discussion

Authorized software programs can be limited to specific versions or from a specific source. To facilitate a comprehensive authorized software process and increase the strength of protection for attacks that bypass application level authorized software, software programs may be decomposed into and monitored at different levels of detail. These levels include applications, application programming interfaces, application modules, scripts, system processes, system services, kernel functions, registries, drivers, and dynamic link libraries. The concept of permitting the execution of authorized software may also be applied to user actions, system ports and protocols, IP addresses/ranges, websites, and MAC addresses. Organizations consider verifying the integrity of authorized software programs using digital signatures, cryptographic checksums, or hash functions. Verification of authorized software can occur either prior to execution or at system startup. The identification of authorized URLs for websites is addressed in [CA-3(5)](#ca-3.5) and [SC-7](#sc-7).

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

Manage and retain information within the system and information output from the system in accordance with applicable laws, executive orders, directives, regulations, policies, standards, guidelines and operational requirements.

Discussion

Information management and retention requirements cover the full life cycle of information, in some cases extending beyond system disposal. Information to be retained may also include policies, procedures, plans, reports, data output from control implementation, and other types of administrative information. The National Archives and Records Administration (NARA) provides federal policy and guidance on records retention and schedules. If organizations have a records management office, consider coordinating with records management personnel. Records produced from the output of implemented controls that may require management and retention include, but are not limited to: All XX-1, [AC-6(9)](#ac-6.9), [AT-4](#at-4), [AU-12](#au-12), [CA-2](#ca-2), [CA-3](#ca-3), [CA-5](#ca-5), [CA-6](#ca-6), [CA-7](#ca-7), [CA-8](#ca-8), [CA-9](#ca-9), [CM-2](#cm-2), [CM-3](#cm-3), [CM-4](#cm-4), [CM-6](#cm-6), [CM-8](#cm-8), [CM-9](#cm-9), [CM-12](#cm-12), [CM-13](#cm-13), [CP-2](#cp-2), [IR-6](#ir-6), [IR-8](#ir-8), [MA-2](#ma-2), [MA-4](#ma-4), [PE-2](#pe-2), [PE-8](#pe-8), [PE-16](#pe-16), [PE-17](#pe-17), [PL-2](#pl-2), [PL-4](#pl-4), [PL-7](#pl-7), [PL-8](#pl-8), [PM-5](#pm-5), [PM-8](#pm-8), [PM-9](#pm-9), [PM-18](#pm-18), [PM-21](#pm-21), [PM-27](#pm-27), [PM-28](#pm-28), [PM-30](#pm-30), [PM-31](#pm-31), [PS-2](#ps-2), [PS-6](#ps-6), [PS-7](#ps-7), [PT-2](#pt-2), [PT-3](#pt-3), [PT-7](#pt-7), [RA-2](#ra-2), [RA-3](#ra-3), [RA-5](#ra-5), [RA-8](#ra-8), [SA-4](#sa-4), [SA-5](#sa-5), [SA-8](#sa-8), [SA-10](#sa-10), [SI-4](#si-4), [SR-2](#sr-2), [SR-4](#sr-4), [SR-8](#sr-8).