Security Audit Logging

Security audit logging is the practice of systematically recording security-relevant events within an application and infrastructure to create an immutable trail of actions. Unlike application logging for debugging, security audit logs specifically capture who did what, when, from where, and whether it succeeded or failed. These logs are essential for detecting active attacks, investigating incidents after the fact, meeting compliance requirements, and understanding normal vs. anomalous behavior.

Critical events to log include: authentication attempts (successful and failed), authorization failures, privilege escalation, administrative actions, data access and modifications (especially to sensitive records), API key creation and usage, configuration changes, input validation failures (potential attack probes), and session lifecycle events. Each log entry should contain a timestamp, actor identity, source IP, action performed, target resource, outcome (success/failure), and relevant context without including sensitive data like passwords or tokens.

Audit logs must be stored securely and separately from application logs to prevent tampering by compromised applications. They should be shipped to a centralized, append-only logging system (like AWS CloudTrail, a SIEM solution, or an immutable log store) with integrity verification. Retention policies should meet both operational needs and compliance requirements (PCI DSS requires 1 year, HIPAA requires 6 years). Automated alerting on suspicious patterns (multiple failed logins, unusual access times, privilege escalation) transforms passive logs into active security monitoring.