What Server Logs Reveal About Attackers: Analyzing Suspicious Requests on Linux
Server logs provide critical insights into potential intrusions by recording events from the operating system, SSH authentication, and web applications. The guide explains how to examine Linux system journals with journalctl, review authentication logs on Debian and RHEL systems, and inspect Nginx access logs for unusual HTTP requests. Analysts learn to identify patterns such as rapid failed login attempts using multiple usernames from a single IP address, which may indicate brute-force or automated scanning activity. The article also covers counting the most active IP addresses with awk and sort commands while stressing the need to compare findings against normal traffic baselines. Additional recommendations include logging structured security events in JSON format with fields for timestamp, user ID, resource, and outcome, following OWASP guidelines. The text warns against storing sensitive data like passwords in logs and highlights limitations such as possible log tampering or unsynchronized server clocks. A practical seven-step investigation plan helps responders preserve evidence and verify hypotheses before taking action.
HabrOct 22, 2026Translated from Russian
