Microsoft 365 Inbox Forwarding Rule Created

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Identifies when a new Inbox forwarding rule is created in Microsoft 365. Inbox rules process messages in the Inbox based on conditions and take actions. In this case, the rules will forward the emails to a defined address. Attackers can abuse Inbox Rules to intercept and exfiltrate email data without making organization-wide configuration changes or having the corresponding privileges.

Rule type: query

Rule indices:

  • filebeat-*
  • logs-o365*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-30m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Domain: Cloud
  • Data Source: Microsoft 365
  • Use Case: Configuration Audit
  • Tactic: Collection

Version: 102

Rule authors:

  • Elastic
  • Gary Blackwell
  • Austin Songer

Rule license: Elastic License v2

Investigation guide

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Rule query

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event.dataset:o365.audit and event.provider:Exchange and
event.category:web and event.action:("New-InboxRule" or "Set-InboxRule") and
    (
        o365.audit.Parameters.ForwardTo:* or
        o365.audit.Parameters.ForwardAsAttachmentTo:* or
        o365.audit.Parameters.RedirectTo:*
    )
    and event.outcome:success

Framework: MITRE ATT&CKTM