Common Log Sources for SIEM

Updated on June 3, 2025

Logs are essential to cybersecurity, providing critical data on events and activities across IT systems. SIEM platforms use this data to detect threats, analyze trends, and ensure compliance. This guide outlines the key log sources for SIEM systems and their role in strengthening security.

Definition and Core Concepts

Log sources in the context of SIEM refer to the systems, devices, and applications within an IT environment that generate records of events and activity. A SIEM collects, normalizes, and analyzes these logs to identify threats, provide visibility, and support compliance. Below are the fundamental terms you’ll encounter when discussing SIEM log sources:

• SIEM (Security Information and Event Management): A platform that consolidates and analyzes log data to detect threats, manage security incidents, and maintain regulatory compliance.
• Log Data: Information captured by systems or devices about activity and events.
• Event: An action or occurrence recorded in the system (e.g., login attempts, file modifications).
• System: IT infrastructure, such as servers, endpoints, and network devices, that generates logs.
• Device: Hardware like firewalls or routers that produce log records of traffic and operations.
• Application: Software or services running in your environment, generating logs for monitoring and troubleshooting.
• Collection: The process of gathering logs from various sources into a centralized system.
• Normalization: The transformation of various log formats into a unified structure suitable for analysis.
• Analysis: The examination of log data by the SIEM to uncover threats, anomalies, and patterns.

Common Log Sources

Firewalls

Firewalls act as a frontline defense for any network, controlling inbound and outbound traffic based on predetermined rules. They produce extensive logs that are critical for monitoring network activity. Key data includes:

• Connection Logs: Logs tracking whether connections were accepted or denied.
• Traffic Logs: Details about source and destination IPs, ports, and communication protocols.
• Security Events: Alerts for intrusion attempts, policy violations, and malware detection.

These logs provide visibility into potential reconnaissance activities, unauthorized access attempts, and blocked traffic.

Endpoints (Workstations and Servers)

Endpoints serve as entry points for user activity and are often targeted in cyberattacks. Logs here are key to detecting early-stage threats. Common endpoint logs include:

• Operating System Logs:
  • Security logs recording logon events, privilege changes, and policy accesses.
  • System logs capturing operational events like process starts/stops.
  • Application logs detailing specific software usage or issues.
• Endpoint Detection and Response (EDR) Logs:
  • Behavioral analysis data pinpointing unusual activity patterns.
  • Threat detection alerts, such as malware execution or anomalous file modifications.
• Authentication Logs:
  • Logs of successful and failed login attempts to monitor identity misuse.

Endpoint logs aid SIEMs in detecting unauthorized access, malware spread, and insider threats.

Intrusion Detection and Prevention Systems (IDPS)

IDPS tools actively monitor and defend networks against potential threats. By processing their logs, SIEMs gain insights into suspicious network traffic.

Logs of importance include:

• Alert Logs: Signatures of detected attacks or triggered specific alert rules.
• Traffic Logs: Anomalous data communication patterns, such as bandwidth spikes or illegitimate packets.

Network Devices (Routers, Switches)

Routers and switches keep network traffic moving and provide vital logs for operational and security monitoring.

• Syslog: General network events and health, such as interface status changes.
• Authentication Logs: Logs of AAA (Authentication, Authorization, Accounting) activity, essential for access control.
• Routing Protocol Events: Logs monitoring disruptions or changes in network paths.

Analyzing these logs allows proactive detection of misconfigurations or network-based exploits.

Servers (Application, Web, Database)

Servers store and process critical data. Their logs disclose everything from operational issues to potential exploits. They include:

• Application Logs: Errors, transaction records, and user activity.
• Web Server Logs: HTTP/HTTPS requests, response codes, and analytics on website usage.
• Database Logs: Queries, login attempts, and access changes.
• Authentication Logs: User sign-in events for identity verification.

Server data is pivotal for detecting database breaches, web exploitation, and application misuse.

Cloud Services

With cloud computing integral to modern IT, cloud services also generate rich log data. These logs ensure visibility over hybrid and remote environments:

• Audit Logs: User activities like file access or configuration changes.
• Access Logs: Who accessed what resources and when.
• Security Logs: Threat detections and compliance vulnerabilities.

By ingesting cloud service logs, a SIEM creates a unified security outlook across on-premise and cloud infrastructure.

Authentication Systems (Active Directory, LDAP)

Authentication systems like Microsoft Active Directory and LDAP secure and manage identity access within corporate infrastructures. Key log data includes:

• Authentication Attempts: Successes and failures, highlighting account compromise attempts.
• Account Management Events: Changes in user roles, password resets, and account creations.

Such logs help enforce identity-based security measures and monitor unauthorized access attempts.

Key Features and Importance of Log Sources

Log sources are essential for core SIEM capabilities. Here’s why they matter:

• Visibility into Security Events: Logs from various sources collectively create a comprehensive picture of your environment’s activity. 
• Detection of Malicious Activity: SIEM systems correlate data across sources to detect advanced persistent threats (APTs), zero-day exploits, or insider misuse. 
• Compliance Requirements: Regulatory standards like GDPR and PCI DSS often require log collection for evidence and reporting. 
• Incident Investigation: Log records provide detailed timelines for forensic analysis after an attack. 
• Trend Analysis: By studying logs over time, you can anticipate and prevent future threats.

Key Terms Appendix

• SIEM: Security Information and Event Management, a system that collects and analyzes logs for security monitoring. 
• Log Data: Records of events and activity generated by systems, devices, and applications. 
• Firewall: Technology that monitors and controls network traffic. 
• Endpoint: Devices like workstations and servers used for organizational operations. 
• EDR: Endpoint Detection and Response, a cybersecurity solution for advanced endpoint monitoring. 
• IDPS: Intrusion Detection and Prevention System, a tool actively monitoring network traffic. 
• Syslog: A protocol used to send system logs from network devices. 
• Active Directory: A Microsoft product managing user identities in enterprise environments. 
• LDAP: Lightweight Directory Access Protocol, an application protocol used to access and maintain distributed directory information.