Scheduled TaskCache Change by Uncommon Program

Hunt Hypothesis

Monitor the creation of a new key under ‘TaskCache’ when a new scheduled task is registered by a process that is not svchost.exe, which is suspicious

Detection Rule

Sigma (Original)

title: Scheduled TaskCache Change by Uncommon Program
id: 4720b7df-40c3-48fd-bbdf-fd4b3c464f0d
status: test
description: Monitor the creation of a new key under 'TaskCache' when a new scheduled task is registered by a process that is not svchost.exe, which is suspicious
references:
    - https://thedfirreport.com/2021/03/29/sodinokibi-aka-revil-ransomware/
    - https://labs.f-secure.com/blog/scheduled-task-tampering/
author: Syed Hasan (@syedhasan009)
date: 2021-06-18
modified: 2025-10-22
tags:
    - attack.privilege-escalation
    - attack.execution
    - attack.persistence
    - attack.t1053
    - attack.t1053.005
logsource:
    category: registry_set
    product: windows
detection:
    selection:
        TargetObject|contains: 'SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\'
    filter_main_empty:
        Details: '(Empty)'
    filter_main_null:
        Details: null
    filter_main_other:
        TargetObject|contains:
            - 'Microsoft\Windows\UpdateOrchestrator'
            - 'Microsoft\Windows\SoftwareProtectionPlatform\SvcRestartTask\Index'
            - 'Microsoft\Windows\Flighting\OneSettings\RefreshCache\Index'
    filter_main_mousocoreworker:
        Image|endswith: 'C:\Windows\System32\MoUsoCoreWorker.exe'
    filter_main_services:
        Image|endswith: 'C:\Windows\System32\services.exe'
    filter_main_tiworker:
        Image|startswith: 'C:\Windows\'
        Image|endswith: '\TiWorker.exe'
    filter_main_svchost:
        Image: 'C:\WINDOWS\system32\svchost.exe'
    filter_main_ngen:
        Image|startswith: 'C:\Windows\Microsoft.NET\Framework' # \Framework\ and \Framework64\
        Image|endswith: '\ngen.exe'
        TargetObject|contains:
            - '\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tasks\{B66B135D-DA06-4FC4-95F8-7458E1D10129}'
            - '\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree\Microsoft\Windows\.NET Framework\.NET Framework NGEN'
    filter_main_office:
        Image:
            - 'C:\Program Files\Microsoft Office\root\Integration\Integrator.exe'
            - 'C:\Program Files (x86)\Microsoft Office\root\Integration\Integrator.exe'
            - 'C:\Program Files\Common Files\microsoft shared\ClickToRun\OfficeC2RClient.exe'
            - 'C:\Program Files (x86)\Common Files\microsoft shared\ClickToRun\OfficeC2RClient.exe'
    filter_main_msiexec:
        Image: 'C:\Windows\System32\msiexec.exe'
    filter_main_explorer:
        Image: 'C:\Windows\explorer.exe'
        TargetObject|contains: '\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree\Microsoft\Windows\PLA\Server Manager Performance Monitor\'
    filter_main_system:
        Image: 'System'
    filter_main_runtimebroker:
        Image: 'C:\Windows\System32\RuntimeBroker.exe'
    filter_optional_dropbox_updater:
        Image:
            - 'C:\Program Files (x86)\Dropbox\Update\DropboxUpdate.exe'
            - 'C:\Program Files\Dropbox\Update\DropboxUpdate.exe'
    filter_optional_edge:
        Image|endswith:
            - 'C:\Program Files (x86)\Microsoft\EdgeUpdate\MicrosoftEdgeUpdate.exe'
            - 'C:\Program Files\Microsoft\EdgeUpdate\MicrosoftEdgeUpdate.exe'
    filter_optional_onedrive:
        Image|endswith:
            - 'C:\Program Files (x86)\Microsoft OneDrive\OneDrive.exe'
            - 'C:\Program Files\Microsoft OneDrive\OneDrive.exe'
    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Unknown
level: high

KQL (Azure Sentinel)

imRegistry
| where RegistryKey endswith "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Schedule\\TaskCache*" and (not((RegistryValueData =~ "(Empty)" or isnull(RegistryValueData) or (RegistryKey contains "Microsoft\\Windows\\UpdateOrchestrator" or RegistryKey contains "Microsoft\\Windows\\SoftwareProtectionPlatform\\SvcRestartTask\\Index" or RegistryKey contains "Microsoft\\Windows\\Flighting\\OneSettings\\RefreshCache\\Index") or ActingProcessName endswith "C:\\Windows\\System32\\MoUsoCoreWorker.exe" or ActingProcessName endswith "C:\\Windows\\System32\\services.exe" or (ActingProcessName startswith "C:\\Windows\\" and ActingProcessName endswith "\\TiWorker.exe") or ActingProcessName =~ "C:\\WINDOWS\\system32\\svchost.exe" or (ActingProcessName startswith "C:\\Windows\\Microsoft.NET\\Framework" and ActingProcessName endswith "\\ngen.exe" and (RegistryKey contains "\\Microsoft\\Windows NT\\CurrentVersion\\Schedule\\TaskCache\\Tasks\\{B66B135D-DA06-4FC4-95F8-7458E1D10129}" or RegistryKey contains "\\Microsoft\\Windows NT\\CurrentVersion\\Schedule\\TaskCache\\Tree\\Microsoft\\Windows\\.NET Framework\\.NET Framework NGEN")) or (ActingProcessName in~ ("C:\\Program Files\\Microsoft Office\\root\\Integration\\Integrator.exe", "C:\\Program Files (x86)\\Microsoft Office\\root\\Integration\\Integrator.exe", "C:\\Program Files\\Common Files\\microsoft shared\\ClickToRun\\OfficeC2RClient.exe", "C:\\Program Files (x86)\\Common Files\\microsoft shared\\ClickToRun\\OfficeC2RClient.exe")) or ActingProcessName =~ "C:\\Windows\\System32\\msiexec.exe" or (ActingProcessName =~ "C:\\Windows\\explorer.exe" and RegistryKey endswith "\\Microsoft\\Windows NT\\CurrentVersion\\Schedule\\TaskCache\\Tree\\Microsoft\\Windows\\PLA\\Server Manager Performance Monitor*") or ActingProcessName =~ "System" or ActingProcessName =~ "C:\\Windows\\System32\\RuntimeBroker.exe"))) and (not(((ActingProcessName in~ ("C:\\Program Files (x86)\\Dropbox\\Update\\DropboxUpdate.exe", "C:\\Program Files\\Dropbox\\Update\\DropboxUpdate.exe")) or (ActingProcessName endswith "C:\\Program Files (x86)\\Microsoft\\EdgeUpdate\\MicrosoftEdgeUpdate.exe" or ActingProcessName endswith "C:\\Program Files\\Microsoft\\EdgeUpdate\\MicrosoftEdgeUpdate.exe") or (ActingProcessName endswith "C:\\Program Files (x86)\\Microsoft OneDrive\\OneDrive.exe" or ActingProcessName endswith "C:\\Program Files\\Microsoft OneDrive\\OneDrive.exe"))))

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Tactic: Privilege Escalation
• Tactic: Execution
• Tactic: Persistence
• Technique: T1053 — T1053
• Technique: T1053.005 — T1053.005

References

• https://thedfirreport.com/2021/03/29/sodinokibi-aka-revil-ransomware/
• https://labs.f-secure.com/blog/scheduled-task-tampering/
• SigmaHQ Rule