Detection: Windows Office Product Loading Taskschd DLL

Description

The following analytic detects an Office document creating a scheduled task, either through a macro VBA API or by loading taskschd.dll. This detection leverages Sysmon EventCode 7 to identify when Office applications load the taskschd.dll file. This activity is significant as it is a common technique used by malicious macro malware to establish persistence or initiate beaconing. If confirmed malicious, this could allow an attacker to maintain persistence, execute arbitrary commands, or schedule future malicious activities, posing a significant threat to the environment.

Search

1`sysmon` EventCode=7 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") loaded_file_path = "*\\taskschd.dll" 
2| stats min(_time) as firstTime max(_time) as lastTime count by user_id, dest, process_name,loaded_file, loaded_file_path, original_file_name, process_guid 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `windows_office_product_loading_taskschd_dll_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 7	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Annotations

Default Configuration

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

Implementation

To successfully implement this search, you need to be ingesting logs with the process name and ImageLoaded (Like sysmon EventCode 7) from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA. Also be sure to include those monitored dll to your own sysmon config.

Known False Positives

False positives may occur if legitimate office documents are creating scheduled tasks. Ensure to investigate the scheduled task and the command to be executed. If the task is benign, add the task name to the exclusion list. Some applications may legitimately load taskschd.dll.

Associated Analytic Story

• Spearphishing Attachments

Risk Based Analytics (RBA)

Risk Message:

An Office document was identified creating a scheduled task on $dest$. Investigate further.

References

• https://research.checkpoint.com/2021/irans-apt34-returns-with-an-updated-arsenal/

• https://redcanary.com/threat-detection-report/techniques/scheduled-task-job/

• https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/trojanized-onenote-document-leads-to-formbook-malware/

Detection Testing

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