Status: To Do
A port monitor can be set through the (Citation: AddMonitor) API call to set a DLL to be loaded at startup. (Citation: AddMonitor) This DLL can be located in <code>C:\Windows\System32</code> and will be loaded by the print spooler service, spoolsv.exe, on boot. The spoolsv.exe process also runs under SYSTEM level permissions. (Citation: Bloxham) Alternatively, an arbitrary DLL can be loaded if permissions allow writing a fully-qualified pathname for that DLL to <code>HKLM\SYSTEM\CurrentControlSet\Control\Print\Monitors</code>.
The Registry key contains entries for the following:
- Local Port
- Standard TCP/IP Port
- USB Monitor
- WSD Port
Adversaries can use this technique to load malicious code at startup that will persist on system reboot and execute as SYSTEM.