Elastic Security Detection Rules

M365 Exchange Inbox Forwarding Rule Created

Last updated 2 months ago on 2026-03-17
Created 5 years ago on 2021-03-29

About

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.
Tags
Domain: CloudDomain: SaaSDomain: EmailData Source: Microsoft 365Data Source: Microsoft 365 Audit LogsUse Case: Configuration AuditTactic: CollectionLanguage: eql
Severity
medium
Risk Score
47
MITRE ATT&CK™

Collection (TA0009)(external, opens in a new tab or window)

↳ Email Collection (T1114)(external, opens in a new tab or window)

False Positive Examples
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.
License
Elastic License v2(external, opens in a new tab or window)

Definition

Rule Type
Event Correlation Rule
Integration Pack
Prebuilt Security Detection Rules
Index Patterns
logs-o365.audit-*filebeat-*
Related Integrations

o365(external, opens in a new tab or window)

Query
text code block:
web where
    event.provider == "Exchange" and
    event.action in ("New-InboxRule", "Set-InboxRule") and
    event.outcome == "success" and
    (
        (?o365.audit.Parameters.ForwardTo != null and not endsWith~(?o365.audit.Parameters.ForwardTo, user.domain)) or
        (?o365.audit.Parameters.ForwardAsAttachmentTo != null and not endsWith~(?o365.audit.Parameters.ForwardAsAttachmentTo, user.domain)) or
        (?o365.audit.Parameters.ForwardingAddress != null and not endsWith~(?o365.audit.Parameters.ForwardingAddress, user.domain)) or
        (?o365.audit.Parameters.ForwardingSmtpAddress != null and not endsWith~(?o365.audit.Parameters.ForwardingSmtpAddress, user.domain)) or
        (?o365.audit.Parameters.RedirectTo != null and not endsWith~(?o365.audit.Parameters.RedirectTo, user.domain)) or
        (?o365.audit.Parameters.RedirectToRecipients != null and not endsWith~(?o365.audit.Parameters.RedirectToRecipients, user.domain))
    )

Install detection rules in Elastic Security

Detect M365 Exchange Inbox Forwarding Rule Created in the Elastic Security detection engine by installing this rule into your Elastic Stack.

To setup this rule, check out the installation guide for Prebuilt Security Detection Rules(external, opens in a new tab or window).