Detection: Windows Office Product Dropped Uncommon File

Updated Date: 2025-01-20 ID: 7ac0fced-9eae-4381-a748-90dcd1aa9393 Author: Teoderick Contreras, Michael Haag, Splunk, TheLawsOfChaos, Github Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects Microsoft Office applications dropping or creating executables or scripts on a Windows OS. It leverages process creation and file system events from the Endpoint data model to identify Office applications like Word or Excel generating files with extensions such as ".exe", ".dll", or ".ps1". This behavior is significant as it is often associated with spear-phishing attacks where malicious files are dropped to compromise the host. If confirmed malicious, this activity could lead to code execution, privilege escalation, or persistent access, posing a severe threat to the environment.

 1
 2| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where `process_office_products` by _time span=1h Processes.process_id Processes.process_name Processes.process Processes.dest Processes.process_guid 
 3| `drop_dm_object_name(Processes)` 
 4| join process_guid, _time [
 5| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_name IN ("*.dll", "*.exe", "*.js", "*.pif", "*.ps1", "*.scr", "*.vbe", "*.vbs") by _time span=1h Filesystem.dest Filesystem.file_create_time Filesystem.file_name Filesystem.process_guid Filesystem.file_path 
 6| `drop_dm_object_name(Filesystem)` 
 7| fields _time dest file_create_time file_name file_path process_name process_path process process_guid] 
 8| dedup file_create_time 
 9| table dest, process_name, process, file_create_time, file_name, file_path, process_guid 
10| `windows_office_product_dropped_uncommon_file_filter`

Data Source

Name Platform Sourcetype Source
Sysmon EventID 1 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Sysmon EventID 11 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Name Value
process_office_products (Processes.process_name IN ("EQNEDT32.exe", "excel.exe", "Graph.exe", "msaccess.exe", "mspub.exe", "onenote.exe", "onenoteim.exe", "onenotem.exe", "outlook.exe", "powerpnt.exe", "visio.exe", "winproj.exe", "winword.exe", "wordpad.exe", "wordview.exe") OR Processes.original_file_name IN ("EQNEDT32.EXE", "Excel.exe", "Graph.exe", "MSACCESS.EXE", "MSPUB.EXE", "OneNote.exe", "OneNoteIm.exe", "OneNoteM.exe", "OUTLOOK.EXE", "POWERPNT.EXE", "VISIO.EXE", "WinProj.exe", "WinWord.exe"))
windows_office_product_dropped_uncommon_file_filter search *
windows_office_product_dropped_uncommon_file_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
T1566 Phishing Initial Access
T1566.001 Spearphishing Attachment Initial Access
Delivery
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

To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA. Tune and filter known instances where renamed rundll32.exe may be used.

Known False Positives

office macro for automation may do this behavior

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

process $process_name$ drops a file $file_name$ in host $dest$

Risk Object Risk Object Type Risk Score Threat Objects
dest system 64 process_name

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog
Integration ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-Sysmon/Operational XmlWinEventLog

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