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registry-actions.md

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Registry Actions

Sysmon has the capability to monitor for three major actions against Registry

  • EventID 12 - Registry object added or deleted

  • EventID 13 - Registry value set

  • EventID 14 - Registry object renamed The Windows Registry has been a source of information gathering, persistence, storage, and configuration control for attackers since its wider use introduction in Windows NT 4.0/Windows 95.

Sysmon uses abbreviated versions of Registry root key names, with the following mappings:

Key name Abbreviation
HKEY_LOCAL_MACHINE HKLM
HKEY_USERS HKU
HKEY_LOCAL_MACHINE\System\ControlSet00x HKLM\System\CurrentControlSet
HKEY_LOCAL_MACHINE\Classes HKCR

Registry Add/Delete Fields:

  • RuleName: Name of rule that triggered the event

  • UtcTime: Time in UTC when event was created

  • EventType: CreateKey or DeleteKey

  • ProcessGuid: Process GUID of the process that created or deleted a registry key

  • ProcessId: Process ID used by the OS to identify the process that created or deleted a registry key

  • Image: File path of the process that created or deleted a registry key

  • TargetObject: Complete path of the registry key

Registry Set Value Fields:

  • RuleName: Name of rule that triggered the event

  • UtcTime: Time in UTC when event was created

  • EventType: SetValue

  • ProcessGuid: Process GUID of the process that modified a registry value

  • ProcessId: Process ID used by the OS to identify the process that modified a registry value

  • Image: File path of the process that modified a registry value

  • TargetObject: Complete path of the modified registry key

  • Details: Details added to the registry key

Registry Rename Fields:

  • RuleName: Name of rule that triggered the event

  • UtcTime: Time in UTC when event was created

  • EventType: RenameKey

  • ProcessGuid: Process GUID of the process that renamed a registry value and key

  • ProcessId: Process ID used by the OS to identify the process that renamed a registry value and key

  • Image: File path of the process that renamed a registry value and key

  • TargetObject: Complete path of the renamed registry key

  • NewName: New name of the registry key

This event type is better used in a targeted manner given the size of the registry and how it is used by a multitude of processes on a daily basis in Windows.

In registry events, the value name is appended to the full key path with a "\" delimiter.

Default key values are named "\(Default)"

When filtering for keys or values in HKCU, use contains or end with when filtering against TargetObject since the SID of the user is appended after the Hive name.

HKCU Test

HKCU Test Event

Since the value name is appended when specifying a registry path in TargetObject, where we also want to catch modification of values under the key, the contains operator is better suited than ends with. For value events, the Detail element of the event will contain the type of value.

Sysmon does not log the actual value being set nor a previous or new one being modified.

HCU Value Event

Example of monitoring some AutoRun locations

<Sysmon schemaversion="4.22">
   <EventFiltering>
 <RuleGroup name="" groupRelation="or">
      <RegistryEvent onmatch="include">
        <TargetObject name="technique_id=T1060,technique_name=Registry Run Keys / Start Folder" condition="contains">\CurrentVersion\Run</TargetObject><!--Microsoft:Windows: Run keys, incld RunOnce, RunOnceEx, RunServices, RunServicesOnce [Also covers terminal server] -->
        <TargetObject condition="contains">\Group Policy\Scripts</TargetObject> <!--Microsoft:Windows: Group policy scripts-->
        <TargetObject name="technique_id=T1037,technique_name=Logon Scripts" condition="contains">\Windows\System\Scripts</TargetObject> <!--Microsoft:Windows: Logon, Loggoff, Shutdown-->
        <TargetObject name="technique_id=T1060,technique_name=Registry Run Keys / Start Folder" condition="contains">\Policies\Explorer\Run</TargetObject><!--Microsoft:Windows -->
        <TargetObject condition="end with">\ServiceDll</TargetObject> <!--Microsoft:Windows: Points to a service's DLL [ https://blog.cylance.com/windows-registry-persistence-part-1-introduction-attack-phases-and-windows-services ] -->
        <TargetObject condition="end with">\ImagePath</TargetObject> <!--Microsoft:Windows: Points to a service's EXE [ https://github.com/crypsisgroup/Splunkmon/blob/master/sysmon.cfg ] -->
        <TargetObject condition="end with">\Start</TargetObject> <!--Microsoft:Windows: Services start mode changes (Disabled, Automatically, Manual)-->
        <TargetObject name="technique_id=T1004,technique_name=Winlogon Helper DLL" condition="begin with">HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Notify</TargetObject><!--Microsoft:Windows: Autorun location [ https://www.cylance.com/windows-registry-persistence-part-2-the-run-keys-and-search-order ] -->
        <TargetObject name="technique_id=T1004,technique_name=Winlogon Helper DLL" condition="begin with">HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Userinit</TargetObject> <!--Microsoft:Windows: Autorun location [ https://www.cylance.com/windows-registry-persistence-part-2-the-run-keys-and-search-order ] -->
        <TargetObject name="technique_id=T1004,technique_name=Winlogon Helper DLL" condition="begin with">HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell</TargetObject>
        <TargetObject condition="begin with">HKLM\SOFTWARE\WOW6432Node\Microsoft\Windows NT\CurrentVersion\Drivers32</TargetObject> <!--Microsoft:Windows: Legacy driver loading | Credit @ion-storm -->
        <TargetObject name="technique_id=T1060,technique_name=Registry Run Keys / Start Folder" condition="begin with">HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\BootExecute</TargetObject> <!--Microsoft:Windows: Autorun | Credit @ion-storm | [ https://www.cylance.com/windows-registry-persistence-part-2-the-run-keys-and-search-order ] -->
        <TargetObject name="technique_id=T1042,technique_name=Change Default File Association" condition="contains">\Explorer\FileExts</TargetObject><!--Microsoft:Windows: Changes to file extension mapping-->
        <TargetObject condition="contains">\shell\install\command</TargetObject> <!--Microsoft:Windows: Sensitive subkey under file associations and CLSID that map to launch command-->
        <TargetObject condition="contains">\shell\open\command</TargetObject> <!--Microsoft:Windows: Sensitive subkey under file associations and CLSID that map to launch command-->
        <TargetObject condition="contains">\shell\open\ddeexec</TargetObject> <!--Microsoft:Windows: Sensitive subkey under file associations and CLSID that map to launch command-->
        <TargetObject name="technique_id=T1060,technique_name=Registry Run Keys / Start Folder" condition="contains">Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders\Startup</TargetObject>
    </RegistryEvent>
</RuleGroup>
</EventFiltering>
</Sysmon>