Detection: O365 Email Receive and Hard Delete Takeover Behavior

Updated Date: 2025-01-20 ID: b66aeaa4-586f-428b-8a2b-c4fd3039d8d3 Author: Steven Dick Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic identifies when an O365 email recipient receives and then deletes emails related to password or banking/payroll changes within a short period. This behavior may indicate a compromised account where the threat actor is attempting to redirect the victims payroll to an attacker controlled bank account.

Search

 1`o365_messagetrace` subject IN ("*banking*","*direct deposit*","*pay-to*","*password *","*passcode *","*OTP *","*MFA *","*Account Recovery*")
 2
 3| eval mailtime = _time
 4
 5| bin _time span=4hr
 6
 7| eval user = lower(RecipientAddress)
 8
 9| eval InternetMessageId = lower(MessageId)
10
11| join InternetMessageId, user max=0
12  [
13  
14| search `o365_management_activity` Workload=Exchange Operation IN ("HardDelete") AND Folder.Path IN ("\\Sent Items","\\Recoverable Items\\Deletions")
15  
16| spath path=AffectedItems{}  output=AffectedItemSplit
17  
18| fields _time,ClientProcessName,ClientIPAddress,ClientInfoString,UserId,Operation,ResultStatus,MailboxOwnerUPN,AffectedItemSplit,Folder.Path 
19  
20| mvexpand AffectedItemSplit 
21| spath input=AffectedItemSplit
22  
23| search Subject IN ("*banking*","*direct deposit*","*pay-to*","*password *","*passcode *","*OTP *","*MFA *","*Account Recovery*") 
24  
25| eval deltime = _time
26  
27| bin _time span=4hr
28  
29| eval InternetMessageId = lower(InternetMessageId), user = lower(UserId), subject = Subject
30  ]
31
32| stats values(ClientIPAddress) as src, values(ClientInfoString) as http_user_agent, values(Folder.Path) as file_path, values(Operation) as signature, values(ResultStatus) as result, values(InternetMessageId) as signature_id, count, min(mailtime) as firstTime, max(deltime) as lastTime by user,subject
33
34| `security_content_ctime(firstTime)` 
35
36| `security_content_ctime(lastTime)`
37
38| `o365_email_receive_and_hard_delete_takeover_behavior_filter`

Data Source

Name	Platform	Sourcetype	Source
Office 365 Reporting Message Trace	N/A	`'o365:reporting:messagetrace'`	`'o365'`
Office 365 Universal Audit Log	N/A	`'o365:management:activity'`	`'o365'`

Macros Used

Name	Value
o365_management_activity	`sourcetype=o365:management:activity`
o365_email_receive_and_hard_delete_takeover_behavior_filter	`search *`

o365_email_receive_and_hard_delete_takeover_behavior_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1070.008	Clear Mailbox Data	Defense Evasion
T1485	Data Destruction	Impact
T1114.001	Local Email Collection	Collection

Actions on Objectives

Exploitation

DE.AE

CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

You must install the Splunk Microsoft Office 365 Add-on and ingest Office 365 management activity events AND Message Trace events.

Known False Positives

Possible new user/account onboarding processes.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

The user $user$ received and deleted an email within a short timeframe titled [$subject$] which may contain password or banking information

Risk Object	Risk Object Type	Risk Score	Threat Objects
user	user	80	src, subject

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`o365`	`o365:management:activity`
Integration	✅ Passing	Dataset	`o365`	`o365:management:activity`

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: GitHub | Version: 1