Refresh [Assignment: organization-defined systems and system components] from a known, trusted state [Assignment: organization-defined frequency].
DiscussionThis requirement mitigates risk from the APT by reducing the targeting capability of adversaries (i.e., the window of opportunity for the attack). By implementing the concept of non-persistence for selected system components, organizations can provide a known state computing resource for a specific time period that does not give adversaries sufficient time to exploit vulnerabilities in organizational systems and the environments in which those systems operate. Since the APT is a high-end, sophisticated threat regarding capability, intent, and targeting, organizations assume that over an extended period, a percentage of attacks will be successful. Non-persistent system components and system services are activated as required using protected information and are terminated periodically or at the end of sessions. Non-persistence increases the work factor of adversaries attempting to compromise or breach systems. Non-persistence can be achieved by refreshing system components (e.g., periodically reimaging components or using a variety of common virtualization techniques). Non-persistent services can be implemented using “Infrastructure as Code” to automatically build, configure, test, deploy, and manage containers, virtual machines, or new instances of processes on physical machines (both persistent or non-persistent). Periodic refreshes of system components and services do not require organizations to determine whether compromises of components or services have occurred (something that may often be difficult to determine). The refresh of selected 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 system unstable. Refreshes may be done periodically to hinder the ability of adversaries to exploit optimum windows of vulnerabilities. The reimaging of system components includes the reinstallation of firmware, operating systems, and applications from a known, trusted source. Reimaging also includes the installation of patches, reapplication of configuration settings, and refresh of system or application data from a known, trusted source.