The following query utilizes Windows Security EventCode 4698,
A scheduled task was created, to identify suspicious tasks registered on Windows either via schtasks.exe OR TaskService with a command to be executed with a Rundll32. This technique is common in new trickbot that uses rundll32 to load is trickbot downloader. The search will return the first time and last time the task was registered, as well as the
Command to be executed,
Enabled, and whether it is
Hidden or not. schtasks.exe is natively found in
C:\Windows\syswow64. The following DLL(s) are loaded when schtasks.exe or TaskService is launched -
taskschd.dll. If found loaded by another process, it is possible a scheduled task is being registered within that process context in memory. Upon triage, identify the task scheduled source. Was it schtasks.exe or via TaskService? Review the job created and the Command to be executed. Capture any artifacts on disk and review. Identify any parallel processes within the same timeframe to identify source.'
- Type: TTP
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2021-04-19
- Author: Teoderick Contreras, Splunk
- ID: 75b00fd8-a0ff-11eb-8b31-acde48001122
Kill Chain Phase
1 2 3 4 5 6 7 `wineventlog_security` EventCode=4698 | xmlkv Message | search Command IN ("*rundll32*") | stats count min(_time) as firstTime max(_time) as lastTime by dest, Task_Name, Command, Author, Enabled, Hidden, Arguments | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `schedule_task_with_rundll32_command_trigger_filter`
The SPL above uses the following Macros:
schedule_task_with_rundll32_command_trigger_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
List of fields required to use this analytic.
How To Implement
To successfully implement this search, you need to be ingesting logs with the task schedule (Exa. Security Log EventCode 4698) endpoints. Tune and filter known instances of Task schedule used in your environment.
Known False Positives
Associated Analytic Story
|70.0||70||100||A schedule task process commandline rundll32 arguments $Arguments$ in host $dest$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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