Detectionhightest

Schtasks Creation Or Modification With SYSTEM Privileges

Detects the creation or update of a scheduled task to run with "NT AUTHORITY\SYSTEM" privileges

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Nasreddine Bencherchali (Nextron Systems)Created Thu Jul 28Updated Sat Feb 1589ca78fd-b37c-4310-b3d3-81a023f83936windows

Log Source

WindowsProcess Creation

ProductWindows← raw: windows

CategoryProcess Creation← raw: process_creation

Events generated when a new process is spawned on the system. Covers command-line arguments, parent/child relationships, and process metadata.

Detection Logic

detection:
    selection_root:
        Image|endswith: '\schtasks.exe'
        CommandLine|contains:
            - ' /change '
            - ' /create '
    selection_run:
        CommandLine|contains: '/ru '
    selection_user:
        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
    filter_optional_teamviewer:
        # FP from test set in SIGMA
        # Cannot use ParentImage on all OSes for 4688 events
        # ParentImage|contains|all:
        #     - '\AppData\Local\Temp\'
        #     - 'TeamViewer_.exe'
        Image|endswith: '\schtasks.exe'
        CommandLine|contains|all:
            - '/TN TVInstallRestore'
            - '\TeamViewer_.exe'
    filter_optional_office:
        CommandLine|contains|all:
            # https://answers.microsoft.com/en-us/msoffice/forum/all/office-15-subscription-heartbeat-task-created-on/43ab5e53-a9fb-47c6-8c14-44889974b9ff
            - 'Subscription Heartbeat'
            - '\HeartbeatConfig.xml'
            - '\Microsoft Shared\OFFICE'
    filter_optional_avira:
        CommandLine|contains:
            - '/Create /F /RU System /SC WEEKLY /TN AviraSystemSpeedupVerify /TR '
            - ':\Program Files (x86)\Avira\System Speedup\setup\avira_speedup_setup.exe'
            - '/VERIFY /VERYSILENT /NOSTART /NODOTNET /NORESTART" /RL HIGHEST'
    condition: all of selection_* and not 1 of filter_optional_*