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Number Title Impact Priority Subject Area
SI-14 Non-Persistence P0 System And Information Integrity

The organization implements non-persistent Assignment: organization-defined information system components and services that are initiated in a known state and terminated Selection (one or more): upon end of session of use; periodically at Assignment: organization-defined frequency.
This control mitigates risk from advanced persistent threats (APTs) by significantly reducing the targeting capability of adversaries (i.e., window of opportunity and available attack surface) to initiate and complete cyber attacks. By implementing the concept of non-persistence for selected information system components, organizations can provide a known state computing resource for a specific period of time that does not give adversaries sufficient time on target to exploit vulnerabilities in organizational information systems and the environments in which those systems operate. Since the advanced persistent threat is a high-end threat with regard to capability, intent, and targeting, organizations assume that over an extended period of time, a percentage of cyber attacks will be successful. Non-persistent information system components and services are activated as required using protected information and terminated periodically or upon the end of sessions. Non-persistence increases the work factor of adversaries in attempting to compromise or breach organizational information systems.
Non-persistent system components can be implemented, for example, by periodically re-imaging components or by using a variety of common virtualization techniques. Non-persistent services can be implemented using virtualization techniques as part of virtual machines or as new instances of processes on physical machines (either persistent or non-persistent).The benefit of periodic refreshes of information system components/services is that it does not require organizations to first determine whether compromises of components or services have occurred (something that may often be difficult for organizations to determine). The refresh of selected information system components and services occurs with sufficient frequency to prevent the spread or intended impact of attacks, but not with such frequency that it makes the information system unstable. In some instances, refreshes of critical components and services may be done periodically in order to hinder the ability of adversaries to exploit optimum windows of vulnerabilities.

SI-14 (1) Refresh From Trusted Sources
Trusted sources include, for example, software/data from write-once, read-only media or from selected off-line secure storage facilities.

The organization ensures that software and data employed during information system component and service refreshes are obtained from Assignment: organization-defined trusted sources.