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Handling False-Positive Malicious URL Alerts for Trusted SaaS Tools

Applies to: Microsoft Defender for Office 365 Audience: IT Admins, SOC Analysts, Tier 2 Support Purpose: Reduce alert noise while maintaining security controls

Overview

Microsoft Defender may generate potentially malicious URL alerts for legitimate SaaS tools such as Scribe, HubSpot, or Zoom. This document provides a standardized process for validating, resolving, and preventing repeat alerts while maintaining security controls.

When to Use This Procedure

Use this procedure only when the sender is trusted, the SaaS platform is approved, the activity aligns with business use, and no indicators of compromise are present.

Step 1: Validate the Alert

  1. Open Microsoft 365 Defender.
    2. Navigate to Incidents & alerts → Alerts.
    3. Open the malicious URL alert.
    4. Validate user, sender, domain, and business context.

Step 2: Resolve the Alert

In the alert management pane, set Status to Resolved, Classification to False Positive, and Determination to Allowed URL or Trusted SaaS. Add the approved remediation comment.

Step 3: Tenant Allow/Block List

Navigate to Email & collaboration → Policies & rules → Threat policies → Tenant Allow/Block List. Add the trusted SaaS domain as an allowed URL for the organization.

Step 4: Alert Tuning (Optional)

If alerts persist, configure alert tuning rules to reduce severity or suppress repeated false positives for validated SaaS domains.

Step 5: Advanced Delivery (Last Resort)

If allowlisting is insufficient, configure Advanced Delivery for the domain. Use with caution and security approval.

Trusted SaaS Governance

Maintain an approved list of SaaS domains and review quarterly to ensure continued business relevance and security compliance.