LoFP LoFP / legitimate scheduled tasks may be created during installation of new software.

Techniques

Sample rules

A scheduled task was updated

Description

Indicates the update of a scheduled task using Windows event logs. Adversaries can use these to establish persistence, by changing the configuration of a legit scheduled task. Some changes such as disabling or enabling a scheduled task are common and may may generate noise.

Detection logic

iam where event.action == "scheduled-task-updated" and

 /* excluding tasks created by the computer account */
 not user.name : "*$" and 
 not winlog.event_data.TaskName : "*Microsoft*" and 
 not winlog.event_data.TaskName :
          ("\\User_Feed_Synchronization-*",
           "\\OneDrive Reporting Task-S-1-5-21*",
           "\\OneDrive Reporting Task-S-1-12-1-*",
           "\\Hewlett-Packard\\HP Web Products Detection",
           "\\Hewlett-Packard\\HPDeviceCheck", 
           "\\Microsoft\\Windows\\UpdateOrchestrator\\UpdateAssistant", 
           "\\IpamDnsProvisioning",  
           "\\Microsoft\\Windows\\UpdateOrchestrator\\UpdateAssistantAllUsersRun", 
           "\\Microsoft\\Windows\\UpdateOrchestrator\\UpdateAssistantCalendarRun", 
           "\\Microsoft\\Windows\\UpdateOrchestrator\\UpdateAssistantWakeupRun", 
           "\\Microsoft\\Windows\\.NET Framework\\.NET Framework NGEN v*", 
           "\\Microsoft\\VisualStudio\\Updates\\BackgroundDownload") and 
  not winlog.event_data.SubjectUserSid :  ("S-1-5-18", "S-1-5-19", "S-1-5-20")

Temporarily Scheduled Task Creation

Description

Indicates the creation and deletion of a scheduled task within a short time interval. Adversaries can use these to proxy malicious execution via the schedule service and perform clean up.

Detection logic

sequence by winlog.computer_name, winlog.event_data.TaskName with maxspan=5m
   [iam where event.action == "scheduled-task-created" and not user.name : "*$"]
   [iam where event.action == "scheduled-task-deleted" and not user.name : "*$"]

Scheduled Task Created by a Windows Script

Description

A scheduled task was created by a Windows script via cscript.exe, wscript.exe or powershell.exe. This can be abused by an adversary to establish persistence.

Detection logic

sequence by host.id with maxspan = 30s
  [any where host.os.type == "windows" and 
    (event.category : ("library", "driver") or (event.category == "process" and event.action : "Image loaded*")) and
    (?dll.name : "taskschd.dll" or file.name : "taskschd.dll") and
    process.name : ("cscript.exe", "wscript.exe", "powershell.exe", "pwsh.exe", "powershell_ise.exe")]
  [registry where host.os.type == "windows" and registry.path : (
    "HKLM\\SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Schedule\\TaskCache\\Tasks\\*\\Actions",
    "\\REGISTRY\\MACHINE\\SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Schedule\\TaskCache\\Tasks\\*\\Actions")]

A scheduled task was created

Description

Indicates the creation of a scheduled task using Windows event logs. Adversaries can use these to establish persistence, move laterally, and/or escalate privileges.

Detection logic

iam where event.action == "scheduled-task-created" and

 /* excluding tasks created by the computer account */
 not user.name : "*$" and

 /* TaskContent is not parsed, exclude by full taskname noisy ones */
 not winlog.event_data.TaskName : (
              "\\CreateExplorerShellUnelevatedTask",
              "\\Hewlett-Packard\\HPDeviceCheck",
              "\\Hewlett-Packard\\HP Support Assistant\\WarrantyChecker",
              "\\Hewlett-Packard\\HP Support Assistant\\WarrantyChecker_backup",
              "\\Hewlett-Packard\\HP Web Products Detection",
              "\\Microsoft\\VisualStudio\\Updates\\BackgroundDownload",
              "\\OneDrive Standalone Update Task-S-1-5-21*",
              "\\OneDrive Standalone Update Task-S-1-12-1-*"
 )

Local Scheduled Task Creation

Description

Indicates the creation of a scheduled task. Adversaries can use these to establish persistence, move laterally, and/or escalate privileges.

Detection logic

sequence with maxspan=1m
  [process where host.os.type == "windows" and event.type != "end" and
    ((process.name : ("cmd.exe", "wscript.exe", "rundll32.exe", "regsvr32.exe", "wmic.exe", "mshta.exe",
                      "powershell.exe", "pwsh.exe", "powershell_ise.exe", "WmiPrvSe.exe", "wsmprovhost.exe", "winrshost.exe") or
    process.pe.original_file_name : ("cmd.exe", "wscript.exe", "rundll32.exe", "regsvr32.exe", "wmic.exe", "mshta.exe",
                                     "powershell.exe", "pwsh.dll", "powershell_ise.exe", "WmiPrvSe.exe", "wsmprovhost.exe",
                                     "winrshost.exe")) or
    ?process.code_signature.trusted == false)] by process.entity_id
  [process where host.os.type == "windows" and event.type == "start" and
    (process.name : "schtasks.exe" or process.pe.original_file_name == "schtasks.exe") and
    process.args : ("/create", "-create") and process.args : ("/RU", "/SC", "/TN", "/TR", "/F", "/XML") and
    /* exclude SYSTEM Integrity Level - look for task creations by non-SYSTEM user */
    not (?process.Ext.token.integrity_level_name : "System" or ?winlog.event_data.IntegrityLevel : "System")
  ] by process.parent.entity_id

Outbound Scheduled Task Activity via PowerShell

Description

Identifies the PowerShell process loading the Task Scheduler COM DLL followed by an outbound RPC network connection within a short time period. This may indicate lateral movement or remote discovery via scheduled tasks.

Detection logic

sequence by host.id, process.entity_id with maxspan = 5s
 [any where host.os.type == "windows" and (event.category == "library" or (event.category == "process" and event.action : "Image loaded*")) and
  (?dll.name : "taskschd.dll" or file.name : "taskschd.dll") and process.name : ("powershell.exe", "pwsh.exe", "powershell_ise.exe")]
 [network where host.os.type == "windows" and process.name : ("powershell.exe", "pwsh.exe", "powershell_ise.exe") and destination.port == 135 and not destination.address in ("127.0.0.1", "::1")]