Microsoft Defender Alert [RULE-1820]
This rule detects high-priority alerts from Microsoft Defender that are forwarded to Microsoft Sentinel. Microsoft Defender includes various security products such as Defender for Endpoint, Defender for Office 365, Defender for Identity, and Defender for Cloud Apps. This rule centralizes all Defender alerts in Sentinel for unified security monitoring and incident response.
When Microsoft Defender detects a threat - such as malware, phishing, suspicious sign-ins, or anomalous behavior - it generates an alert with detailed information about the threat, affected entities (devices, users, files, emails), and recommended response actions. This rule filters on high-severity alerts and aggregates all related evidence for effective triage.
Rationale
Microsoft Defender is your first line of defense against cyber threats in the Microsoft 365 environment. It continuously monitors endpoints, email, identities, and cloud apps for suspicious activity. However, Defender alerts come in through various portals (Microsoft 365 Defender, Defender for Endpoint, etc.) and can easily be overlooked without centralized monitoring.
By sending Defender alerts to Sentinel, your security team gets a unified view of all threats across your environment. High-severity alerts indicate serious threats requiring immediate attention: active malware infections, ongoing phishing campaigns, compromised accounts, or lateral movement by attackers. Ignoring these alerts can lead to data exfiltration, ransomware infections, or complete tenant compromise.
This rule ensures that no high-severity Defender alert goes unnoticed. It aggregates all related entities (which devices, users, files are involved) so your security team immediately has context to begin investigation and remediation. In modern cyber attacks, every minute counts - early detection and rapid response are essential to limit damage.