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Description

The following analytic detects a potentially malicious office document that creates a scheduled task entry either through a macro VBA API or by loading taskschd.dll. This technique has been observed in numerous instances of malicious macro malware aiming to establish persistence or beaconing through task schedule entries. The analytic will return the first and last time the task was registered, as well as details such as the Command to be executed, Task Name, Author, Enabled status, and whether it is Hidden. schtasks.exe is natively located in C:\Windows\system32 and C:\Windows\syswow64. The DLL(s) taskschd.dll are loaded when schtasks.exe or TaskService is initiated. If this DLL is found loaded by another process, it may indicate that a scheduled task is being registered within that process's context in memory. During triage, determine the source of the scheduled task. Was it schtasks.exe or via TaskService? Review the job created and the command to be executed. Capture any artifacts on disk for further review. Identify any parallel processes within the same timeframe to pinpoint the source.'

  • Type: TTP

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2024-03-14
  • Author: Teoderick Contreras, Splunk
  • ID: cc8b7b74-9d0f-11eb-8342-acde48001122

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1566 Phishing Initial Access
T1566.001 Spearphishing Attachment Initial Access
Kill Chain Phase
  • Delivery
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`sysmon` EventCode=7 process_name IN ("WINWORD.EXE", "EXCEL.EXE", "POWERPNT.EXE","onenote.exe","onenotem.exe","onenoteviewer.exe","onenoteim.exe", "msaccess.exe") loaded_file_path = "*\\taskschd.dll" 
| 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 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `office_document_creating_schedule_task_filter`

Macros

The SPL above uses the following Macros:

:information_source: office_document_creating_schedule_task_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.

  • ImageLoaded
  • AllImageLoaded
  • dest
  • EventCode
  • Image
  • process_name
  • ProcessId
  • ProcessGuid
  • _time

How To Implement

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

RBA

Risk Score Impact Confidence Message
49.0 70 70 An Office document was identified creating a scheduled task on $dest$. Investigate further.

:information_source: 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

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: 6