Email files written outside of the Outlook directory

name: Email files written outside of the Outlook directory
id: 8d52cf03-ba25-4101-aa78-07994aed4f74
version: 11
date: '2026-03-10'
author: Bhavin Patel, Splunk
status: experimental
type: TTP
description: The following analytic detects email files (.pst or .ost) being created outside the standard Outlook directories. It leverages the Endpoint.Filesystem data model to identify file creation events and filters for email files not located in "C:\Users\*\My Documents\Outlook Files\*" or "C:\Users\*\AppData\Local\Microsoft\Outlook*". This activity is significant as it may indicate data exfiltration or unauthorized access to email data. If confirmed malicious, an attacker could potentially access sensitive email content, leading to data breaches or further exploitation within the network.
data_source:
    - Sysmon EventID 11
search: |-
    | tstats `security_content_summariesonly` count values(Filesystem.file_path) as file_path min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem
      WHERE (
            Filesystem.file_name=*.pst
            OR
            Filesystem.file_name=*.ost
        )
        Filesystem.file_path != "C:\Users\*\My Documents\Outlook Files\*"  Filesystem.file_path!="C:\Users\*\AppData\Local\Microsoft\Outlook*"
      BY Filesystem.action Filesystem.dest Filesystem.file_access_time
         Filesystem.file_create_time Filesystem.file_hash Filesystem.file_modify_time
         Filesystem.file_name Filesystem.file_path Filesystem.file_acl
         Filesystem.file_size Filesystem.process_guid Filesystem.process_id
         Filesystem.user Filesystem.vendor_product
    | `drop_dm_object_name("Filesystem")`
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `email_files_written_outside_of_the_outlook_directory_filter`
how_to_implement: To successfully implement this search, you must be ingesting data that records the file-system activity from your hosts to populate the Endpoint.Filesystem data model node. This is typically populated via endpoint detection-and-response product, such as Carbon Black, or by other endpoint data sources, such as Sysmon. The data used for this search is typically generated via logs that report file-system reads and writes.
known_false_positives: Administrators and users sometimes prefer backing up their email data by moving the email files into a different folder. These attempts will be detected by the search.
references: []
rba:
    message: Email files written outside of Outlook's Directory on $dest$
    risk_objects:
        - field: dest
          type: system
          score: 50
    threat_objects: []
tags:
    analytic_story:
        - Collection and Staging
    asset_type: Endpoint
    mitre_attack_id:
        - T1114.001
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: endpoint