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: 5 minutes

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

Maximum alerts per execution: 100

References:

Tags:

  • Elastic
  • Cloud
  • Microsoft 365
  • Continuous Monitoring
  • SecOps
  • Configuration Audit

Version: 6 (version history)

Added (Elastic Stack release): 7.13.0

Last modified (Elastic Stack release): 8.4.0

Rule authors: Elastic, Gary Blackwell, Austin Songer

Rule license: Elastic License v2

Potential false positives

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Users and Administrators can create inbox rules for legitimate purposes. Verify if it complies with the company policy and done with the user’s consent. Exceptions can be added to this rule to filter expected behavior.

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" and (
o365.audit.Parameters.ForwardTo:* or
o365.audit.Parameters.ForwardAsAttachmentTo:* or
o365.audit.Parameters.RedirectTo:* ) and event.outcome:success

Threat mapping

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Framework: MITRE ATT&CKTM

Rule version history

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Version 6 (8.4.0 release)
  • Updated query, changed from:

    event.dataset:o365.audit and event.provider:Exchange and
    event.category:web and event.action:"New-InboxRule" and (
    o365.audit.Parameters.ForwardTo:* or
    o365.audit.Parameters.ForwardAsAttachmentTo:* or
    o365.audit.Parameters.RedirectTo:* ) and
    event.outcome:success
Version 4 (8.3.0 release)
  • Updated query, changed from:

    event.dataset:o365.audit and event.provider:Exchange and
    event.category:web and event.action:"New-InboxRule" and (
    o365audit.Parameters.ForwardTo:* or
    o365audit.Parameters.ForwardAsAttachmentTo:* or
    o365audit.Parameters.RedirectTo:* ) and event.outcome:success
Version 3 (8.2.0 release)
  • Formatting only
Version 2 (8.1.0 release)
  • Rule name changed from: Microsoft 365 New Inbox Rule Created
  • Updated query, changed from:

    event.dataset:o365.audit and event.provider:Exchange and
    event.category:web and event.action:"New-InboxRule" and
    event.outcome:success