O365 Mailbox Email Forwarding Enabled
Description
This detection is designed to identify instances where email forwarding has been enabled on mailboxes within an Office 365 environment. By monitoring for the specific operation Set-Mailbox within the o365_management_activity logs, this analytic hones in on changes made to mailbox configurations that initiate the forwarding of emails. It specifically looks for the activation of ForwardingAddress or ForwardingSmtpAddress parameters, indicating that emails are being automatically sent to another email address from the user's mailbox.
- Type: TTP
-
Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Last Updated: 2024-03-26
- Author: Patrick Bareiss, Mauricio Velazco, Splunk
- ID: 0b6bc75c-05d1-4101-9fc3-97e706168f24
Annotations
ATT&CK
Kill Chain Phase
- Exploitation
NIST
- DE.CM
CIS20
- CIS 10
CVE
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`o365_management_activity` Operation=Set-Mailbox
| eval match1=mvfind('Parameters{}.Name', "ForwardingAddress")
| eval match2=mvfind('Parameters{}.Name', "ForwardingSmtpAddress")
| where match1>= 0 OR match2>= 0
| eval ForwardTo=coalesce(ForwardingAddress, ForwardingSmtpAddress)
| search ForwardTo!=""
| rename user_id as user
| stats count earliest(_time) as firstTime latest(_time) as lastTime values(ForwardTo) as ForwardTo by user ObjectId
|`security_content_ctime(firstTime)`
|`security_content_ctime(lastTime)`
| `o365_mailbox_email_forwarding_enabled_filter`
Macros
The SPL above uses the following Macros:
o365_mailbox_email_forwarding_enabled_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Required fields
List of fields required to use this analytic.
- _time
- Operation
- Parameters{}.Name
- src_user
- DeliverToMailboxAndForward
- ObjectId
How To Implement
You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events.
Known False Positives
Email forwarding may be configured for legitimate purposes, filter as needed.
Associated Analytic Story
RBA
Risk Score | Impact | Confidence | Message |
---|---|---|---|
42.0 | 70 | 60 | Email forwarding configured by $user$ on mailbox $ObjectId$ |
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
Reference
- https://attack.mitre.org/techniques/T1114/003/
- https://learn.microsoft.com/en-us/exchange/recipients/user-mailboxes/email-forwarding?view=exchserver-2019
Test Dataset
Replay any dataset to Splunk Enterprise by using our replay.py
tool or the UI.
Alternatively you can replay a dataset into a Splunk Attack Range
source | version: 1