Suspicious Schtasks Schedule Types — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: high. Source dates: 2022-09-09 / not supplied.

{
  "product": "windows",
  "category": "process_creation"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 6355c03228916d530139e47e19432330ad8db1df03fabf37871f240cf37da228

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Suspicious Schtasks Schedule Types
id: 24c8392b-aa3c-46b7-a545-43f71657fe98
related:
    - id: 7a02e22e-b885-4404-b38b-1ddc7e65258a
      type: similar
status: test
description: Detects scheduled task creations or modification on a suspicious schedule type
references:
    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/schtasks-change
    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/schtasks-create
    - http://blog.talosintelligence.com/2022/09/lazarus-three-rats.html
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-09-09
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.execution
    - attack.t1053.005
logsource:
    product: windows
    category: process_creation
detection:
    selection_img:
        - Image|endswith: '\schtasks.exe'
        - OriginalFileName: 'schtasks.exe'
    selection_time:
        CommandLine|contains:
            - ' ONLOGON '
            - ' ONSTART '
            - ' ONCE '
            - ' ONIDLE '
    filter_privs:
        CommandLine|contains:
            - 'NT AUT' # This covers the usual NT AUTHORITY\SYSTEM
            - ' SYSTEM' # SYSTEM is a valid value for schtasks hence it gets it's own value with space
            - 'HIGHEST'
    condition: all of selection_* and not 1 of filter_*
falsepositives:
    - Legitimate processes that run at logon. Filter according to your environment
level: high

Original YAML and metadata in JSON

False positives

• Legitimate processes that run at logon. Filter according to your environment

Source references

• https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/schtasks-change
• https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/schtasks-create
• http://blog.talosintelligence.com/2022/09/lazarus-three-rats.html