# Rule Engine [![[Pasted image 20251104230323.png]]](https://soc-expert.de/From+Logging+to+Alerting+and+Beyond) A **rule engine** is a core component responsible for **analyzing incoming log data and triggering actions** based on predefined logic or conditions. It enables the SIEM to **detect threats, anomalies, and policy violations** in real time or near-real time. ## What Does a Rule Engine Do? ### Evaluates Events Against Rules - It continuously monitors normalized log data and events. - Each event is checked against a set of **correlation rules** or **detection rules**. ### Triggers Alerts or Actions - If an event matches a rule condition, the engine can: - Generate an **alert** - Start an **automated response** (e.g., block IP, disable account) - Log the incident for further investigation ### Supports Complex Logic - Rules can be simple (e.g., failed login attempts > 5) or complex (e.g., multiple failed logins from different IPs followed by a successful login). - Often includes **time-based conditions**, **thresholds**, and **event correlation** across multiple sources. ### Example Rule (Simplified) **Rule Name**: Brute Force Login Detection **Condition**: - More than 5 failed login attempts from the same IP within 2 minutes **Action**: - Generate a high-severity alert - Notify SOC team ### Types of Rules in SIEMs | Rule Type | Description | | -------------------- | --------------------------------------------------------------------------------------- | | **Threshold Rule** | Triggers when a count exceeds a limit (e.g., 100 connections in 1 minute) | | **Correlation Rule** | Links multiple events across systems (e.g., login + file access + privilege escalation) | | **Behavioral Rule** | Detects deviations from normal patterns (e.g., user logs in from a new country) | | **Statistical Rule** | Uses baselines and anomaly detection | | **Custom Rule** | User-defined logic tailored to specific environments | | | | >[!note] Why Is the Rule Engine Important? > > - **Real-time threat detection** > - **Automated incident response** > - **Compliance enforcement** > - **Operational efficiency** ## Use Case A **Use Case** plays a **strategic and operational role**. It defines a specific **security scenario or objective** that the SIEM should detect, monitor, or respond to. Use cases guide the configuration of rules, alerts, dashboards, and reports within the SIEM. A **SIEM use case** is a **defined security goal** that translates into: - What data to collect - What patterns to detect - What rules to apply - What actions to take >[!note] It answers the question: >**“What security issue are we trying to detect or prevent?”** ### Examples of SIEM Use Cases |Use Case|Description| |---|---| |**Brute Force Attack Detection**|Detect multiple failed login attempts from the same IP| |**Privileged Account Abuse**|Monitor unusual activity from admin accounts| |**Data Exfiltration**|Detect large outbound data transfers| |**Malware Infection**|Identify indicators of compromise from endpoint logs| |**Insider Threat**|Track sensitive file access by internal users| |**Suspicious VPN Access**|Alert on VPN logins from unusual geolocations| ### Role of Use Cases in SIEM #### Guides Rule Creation - Use cases define the logic for correlation rules and thresholds. #### Determines Data Requirements - Helps identify which log sources are needed (e.g., firewall, endpoint, AD logs). #### Supports Incident Response - Use cases often include playbooks for how to respond when an alert is triggered. #### Aligns with Business and Compliance Goals - Use cases can be tailored to meet regulatory requirements (e.g., GDPR, HIPAA). #### Improves SIEM Efficiency - Focuses resources on high-value detections rather than generic logging. ### Use Case Lifecycle 1. **Define** – Identify the threat or scenario. 2. **Design** – Create rules, filters, and dashboards. 3. **Deploy** – Implement in the SIEM. 4. **Test** – Validate detection accuracy. 5. **Tune** – Adjust thresholds and logic to reduce false positives. 6. **Review** – Periodically update based on evolving threats.