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Create Remote Thread

Sysmon will log EventID 8 for all processes that use the Win32 API CreateRemoteThread call.

This call is used by some programs, parts of the OS and debuggers making the number of events easy to filter out the normal usages to detect the outliers.

Process of use/abuse of CreateRemoteThread

  • Use OpenProcess( ) to open a target process.

  • Use VirtualAllocEx( ) allocate a chunk of memory in the process.

  • Use WriteProcessMemory( ) write the payload to the newly allocated section.

  • User CreateRemoteThread( ) to create a new thread in the remote process to execute the shellcode.

There are multiple Process Injection techniques, Sysmon monitors for the most common one used. The infographic from http://struppigel.blogspot.com/2017/07/process-injection-info-graphic.html

Illustrates the different techniques.

process injection infograph

The fields for the event are:

  • RuleName: Name of rule that triggered the event.

  • UtcTime: Time in UTC when event was created

  • SourceProcessGuid: Process Guid of the source process that created a thread in another process

  • SourceProcessId: Process ID used by the OS to identify the source process that created a thread in another process

  • SourceImage: File path of the source process that created a thread in another process

  • TargetProcessGuid: Process Guid of the target process

  • TargetProcessId: Process ID used by the OS to identify the target process

  • TargetImage: File path of the target process

  • NewThreadId: Id of the new thread created in the target process

  • StartAddress: New thread start address

  • StartModule: Start module determined from thread start address mapping to PEB loaded module list

  • StartFunction: Start function is reported if exact match to function in image export tables

Since the number of processes that use the CreateRemoteThread() API in a production environment is low, the best approach is to exclude known good processes by their full path. CreateRemoteThread() is not the only API call that can be used to create a thread, so it should not be relied on as a definitive guarantee of lack of process injection.

process

Example where known processes that use the API call are excluded

<Sysmon schemaversion="4.22">
  <CheckRevocation/>
    <EventFiltering>
      <RuleGroup name="" groupRelation="or">
        <CreateRemoteThread onmatch="exclude">
          <!--The process activity of those in the list should be monitored since an-->
          <!--attacker may host his actions in one of these to bypass detection.-->
           <TargetImage condition="end with">
             Google\Chrome\Application\chrome.exe
            </TargetImage>
            <SourceImage condition="is">
              C:\Windows\System32\wbem\WmiPrvSE.exe
            </SourceImage>
            <SourceImage condition="is">
              C:\Windows\System32\svchost.exe
            </SourceImage>
            <SourceImage condition="is">
              C:\Windows\System32\wininit.exe
            </SourceImage>
            <SourceImage condition="is">
              C:\Windows\System32\csrss.exe
            </SourceImage>
            <SourceImage condition="is">
              C:\Windows\System32\services.exe
            </SourceImage>
            <SourceImage condition="is">
              C:\Windows\System32\winlogon.exe
            </SourceImage>
            <SourceImage condition="is">
              C:\Windows\System32\audiodg.exe
            </SourceImage>
            <StartModule condition="is">
              C:\windows\system32\kernel32.dll
            </StartModule>
        </CreateRemoteThread>
        </RuleGroup>
    </EventFiltering>
</Sysmon>