Adversaries may abuse print processors to run malicious DLLs during system boot for persistence and/or privilege escalation. Print processors are DLLs that are loaded by the print spooler service, `spoolsv.exe`, during boot.(Citation: Microsoft Intro Print Processors) Adversaries may abuse the print spooler service by adding print processors that load malicious DLLs at startup. A print processor can be installed through the AddPrintProcessor API call with an account that has SeLoadDriverPrivilege enabled. Alternatively, a print processor can be registered to the print spooler service by adding the HKLM\SYSTEM\\[CurrentControlSet or ControlSet001]\Control\Print\Environments\\[Windows architecture: e.g., Windows x64]\Print Processors\\[user defined]\Driver Registry key that points to the DLL. For the malicious print processor to be correctly installed, the payload must be located in the dedicated system print-processor directory, that can be found with the GetPrintProcessorDirectory API call, or referenced via a relative path from this directory.(Citation: Microsoft AddPrintProcessor May 2018) After the print processors are installed, the print spooler service, which starts during boot, must be restarted in order for them to run.(Citation: ESET PipeMon May 2020) The print spooler service runs under SYSTEM level permissions, therefore print processors installed by an adversary may run under elevated privileges.

Created

Oct 5, 2020, 1:24 PM UTC

Modified

Oct 24, 2025, 5:48 PM UTC