The following analytic identifies a process attempting to delete a scheduled task SD (Security Descriptor) from within the registry path of that task. This may occur from a non-standard process running and may not come from reg.exe. This particular behavior will remove the actual Task Name from the Task Scheduler GUI and from the command-line query - schtasks.exe /query. In addition, in order to perform this action, the user context will need to be SYSTEM.\ Identifying the deletion of a scheduled task's Security Descriptor from the registry is significant for a SOC as it may indicate malicious activity attempting to remove evidence of a scheduled task, potentially for defense evasion purposes. If a true positive is detected, it suggests an attacker with privileged access attempting to remove traces of their activities, which can have a significant impact on the security and functionality of affected systems. Immediate investigation and response are required to mitigate further risks and preserve the integrity of the environment.
- Type: Anomaly
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2022-04-13
- Author: Michael Haag, Splunk
- ID: ffeb7893-ff06-446f-815b-33ca73224e92
Kill Chain Phase
- CIS 10
1 2 3 4 5 6 | tstats `security_content_summariesonly` count from datamodel=Endpoint.Registry where Registry.registry_path IN ("*\\Schedule\\TaskCache\\Tree\\*") Registry.user="SYSTEM" Registry.registry_value_name="SD" (Registry.action=Deleted OR Registry.action=modified) by _time Registry.dest Registry.process_guid Registry.user Registry.registry_path Registry.registry_value_name Registry.registry_key_name Registry.registry_value_data Registry.status Registry.action | `drop_dm_object_name(Registry)` | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `windows_registry_delete_task_sd_filter`
The SPL above uses the following Macros:
windows_registry_delete_task_sd_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 information on process that include the name of the process responsible for the changes from your endpoints into the
Endpoint datamodel in the
Registry node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.
Known False Positives
False positives should be limited as the activity is not common to delete ONLY the SD from the registry. Filter as needed. Update the analytic Modified or Deleted values based on product that is in the datamodel.
Associated Analytic Story
|49.0||70||70||A scheduled task security descriptor was deleted from the registry on $dest$.|
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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