NIST 800-171 3.3.3: Event Review and Update
Event review is your frontline defense against undetected security incidents. NIST 800-171 3.3.3 requires organizations to review and update logged events—ensuring audit trails remain accurate, complete, and actionable for threat detection and compliance audits.
What this means
This control mandates that you regularly examine system and application logs to verify events are captured correctly, remain tamper-proof, and are retained according to organizational policy. 'Update' means correcting inaccuracies, adjusting retention schedules, and ensuring logs reflect actual system activity. For CUI environments, this review process must be documented and repeatable.
How to comply
- 1.Establish a documented event review schedule (daily, weekly, or based on risk) and assign ownership to a security or operations team
- 2.Define which events must be logged across systems, applications, and network devices handling CUI
- 3.Implement centralized log aggregation to consolidate events from all sources into a single platform for easier review
- 4.Create review procedures that document what logs were examined, findings, and any corrective actions taken
- 5.Update log retention policies based on regulatory requirements, business needs, and storage capacity
- 6.Test log integrity mechanisms (hashing, write-once storage) to ensure logged events cannot be altered post-capture
- 7.Document the review process, including frequency, responsible parties, and escalation procedures for suspicious events
Evidence auditors look for
- Log review schedule and evidence of execution (e.g., dated review reports, meeting notes)
- Written event logging policy specifying which systems, events, and data sources require logs
- Centralized log management system configuration and access logs showing regular reviews
- Retention policy documentation aligned with NIST requirements and business continuity needs
- Examples of corrective actions taken based on event reviews (e.g., firewall rule updates, user access changes)
- Log integrity validation reports demonstrating no unauthorized modifications
- Audit trails showing who reviewed logs, when, and what actions were taken
Frequently asked questions
When will FAQs be available?
The FAQ for this control is currently being prepared.
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