CMMC Practice AU.2.042
Create and retain system audit logs and records to the extent needed to enable the monitoring, analysis, investigation, and reporting of unlawful or unauthorized system activity.
Bold Coast Security Guidance
This practice relates specifically to creating and retaining system logs in the environment. The CMMC clarification provides a good list of items which all audit trails should capture. There are specific events which your will always want to log, such as those done by a user with administrative credentials, and others of standard users you may which to limit do the the size of the logs which will be created.
You will want to review whether host based logging is sufficient in your environment, or do you want to employ internal network montioring which can log all activity at the packet level. This level of detail will obviously provide the best forensic data for investigations, but will also have large storage and processing ramifications!
Finally, always log both failures AND success in your logs. A breach is only a breach because an unauthorized party has bypassed the authorization process in some manner and is now taking action successfully. You must be able to trace those actions.
DRAFT NIST SP 800-171 R2
An event is any observable occurrence in a system, which includes unlawful or unauthorized system activity. Organizations identify event types for which a logging functionality is needed as those events which are significant and relevant to the security of systems and the environments in which those systems operate to meet specific and ongoing auditing needs. Event types can include password changes, failed logons or failed accesses related to systems, administrative privilege usage, or third -party credential usage. In determining event types that require logging, organizations consider the monitoring and auditing appropriate for each of the CUI security requirements. Monitoring and auditing requirements can be balanced with other system needs. For example, organizations may determine that systems must have the capability to log every file access both successful and unsuccessful, but not activate that capability except for specific circumstances due to the potential burden on system performance.
Audit records can be generated at various levels of abstraction, including at the packet level as information traverses the network. Selecting the appropriate level of abstraction is a critical aspect of an audit logging capability and can facilitate the identification of root causes to problems. Organizations consider in the definition of event types, the logging necessary to cover related events such as the steps in distributed, transaction- based processes (e.g.,processes that are distributed across multiple organizations) and actions that occur in service-oriented or cloud-based architectures. Audit record content that may be necessary to satisfy this requirement includes time stamps, source and destination addresses, user or process identifiers, event descriptions, success or failure indications, filenames involved, and access control or flow control rules invoked. Event outcomes can include indicators of event success or failure and event- specific results (e.g., the security state of the system after the event occurred).
Detailed information that organizations may consider in audit records includes full text recording of privileged commands or the individual identities of group account users. Organizations consider limiting the additional audit log information to only that information explicitly needed for specific audit requirements . This facilitates the use of audit trails and audit logs by not including information that could potentially be misleading or could make it more difficult to locate information of interest. Audit logs are reviewed and analyzed as often as needed to provide important information to organizations to facilitate risk-based decision making. NIST SP 800-92 provides guidance on security log management.