What are the most important types of logs that a SOC analyst monitors, and what kind of security information can you extract from each type?

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As a SOC analyst, I monitor several critical log types, each providing different but complementary insights into the organization's security posture.

Firewall logs are among the most fundamental. They record all traffic that passes through or is blocked by the firewall, including source and destination IP addresses, ports, protocols, and the action taken, whether the connection was allowed or denied. These logs help me identify unauthorized connection attempts, unusual outbound traffic that could indicate data exfiltration, and port scanning activity from external attackers.

Authentication and access logs track login events across systems. Windows Security Event Logs are particularly valuable, with Event ID 4624 indicating successful logons, Event ID 4625 indicating failed logons, and Event ID 4648 indicating explicit credential usage. By monitoring these logs, I can detect brute-force attacks, credential stuffing, unauthorized access to sensitive systems, and unusual login patterns such as after-hours access or logins from unexpected geographic locations.

Endpoint detection and response logs provide visibility into what is happening on individual workstations and servers. They capture process executions, file modifications, registry changes, and network connections made by applications. These logs are essential for detecting malware execution, suspicious scripts, and lateral movement between systems.

Web proxy logs record all HTTP and HTTPS traffic from internal users to the internet. They reveal which websites and domains users are visiting, downloads initiated, and any attempts to access blocked categories. These logs are valuable for identifying users who visited malicious websites, command and control communication, and policy violations.

DNS logs capture every domain name resolution request made by devices on the network. Since almost all network communication starts with a DNS query, these logs provide an excellent vantage point for detecting connections to known malicious domains, domain generation algorithm activity used by malware, and DNS tunneling attempts.

Email gateway logs track inbound and outbound email activity, including sender and recipient information, attachment details, and spam or phishing verdicts. These logs help me identify phishing campaigns targeting the organization, malicious attachments that bypassed filters, and data loss through email.

Finally, cloud service logs from platforms like AWS CloudTrail, Azure Activity Logs, or Google Cloud Audit Logs provide visibility into actions taken within cloud environments, including API calls, resource modifications, and access changes. As organizations increasingly move to the cloud, these logs are becoming essential for SOC monitoring.