NIST Special Publication 800-171 Revision 2

Discussion:

Information flow control regulates where information can travel within a system and between systems (versus who can access the information) and without explicit regard to subsequent accesses to that information. Flow control restrictions include the following: keeping exportcontrolled information from being transmitted in the clear to the Internet; blocking outside traffic that claims to be from within the organization; restricting requests to the Internet that are not from the internal web proxy server; and limiting information transfers between organizations based on data structures and content. Organizations commonly use information flow control policies and enforcement mechanisms to control the flow of information between designated sources and destinations (e.g., networks, individuals, and devices) within systems and between interconnected systems. Flow control is based on characteristics of the information or the information path. Enforcement occurs in boundary protection devices (e.g., gateways, routers, guards, encrypted tunnels, firewalls) that employ rule sets or establish configuration settings that restrict system services, provide a packetfiltering capability based on header information, or message-filtering capability based on message content (e.g., implementing key word searches or using document characteristics). Organizations also consider the trustworthiness of filtering and inspection mechanisms (i.e., hardware, firmware, and software components) that are critical to information flow enforcement. Transferring information between systems representing different security domains with different security policies introduces risk that such transfers violate one or more domain security policies. In such situations, information owners or stewards provide guidance at designated policy enforcement points between interconnected systems. Organizations consider mandating specific architectural solutions when required to enforce specific security policies. Enforcement includes: prohibiting information transfers between interconnected systems (i.e., allowing access only); employing hardware mechanisms to enforce one-way information flows; and implementing trustworthy regrading mechanisms to reassign security attributes and security labels.

Determining Statements (NIST SP 800-171Ar2)

Upon assessment, assessors must determine if-

3.1.3[a] information flow control policies are defined.
3.1.3[b] methods and enforcement mechanisms for controlling the flow of CUI are
defined.
3.1.3[c] designated sources and destinations (e.g., networks, individuals, and devices)
for CUI within the system and between interconnected systems are identified.
3.1.3[d] authorizations for controlling the flow of CUI are defined.
3.1.3[e] approved authorizations for controlling the flow of CUI are enforced.3.1.2[a] the types of transactions and functions that authorized users are permitted to
execute are defined.
3.1.2[b] system access is limited to the defined types of transactions and functions for
authorized users.

Assessors are instructed to-

Examine: [SELECT FROM: Access control policy; information flow control policies; procedures addressing information flow enforcement; system security plan; system design documentation; system configuration settings and associated documentation; list of information flow authorizations; system baseline configuration; system audit logs and records; other relevant documents or records].

Interview: [SELECT FROM: System or network administrators; personnel with information security responsibilities; system developers].

Test: [SELECT FROM: Mechanisms implementing information flow enforcement policy].