Adversaries may use port monitors to run an adversary supplied DLL during system boot for persistence or privilege escalation. A port monitor can be set through the <code>AddMonitor</code> 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 and run by the print spooler service, spoolsv.exe, under SYSTEM level permissions on boot.(Citation: Bloxham)
Alternatively, an arbitrary DLL can be loaded if permissions allow writing a fully-qualified pathname for that DLL to the Driver value of an existing or new arbitrarily named subkey of <code>HKLM\SYSTEM\CurrentControlSet\Control\Print\Monitors</code>. The Registry key contains entries for the following:
Detection Strategy for T1547.010 – Port Monitor DLL Persistence via spoolsv.exe (Windows)
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