Print Processors

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.¹ 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 <code>AddPrintProcessor</code> API call with an account that has <code>SeLoadDriverPrivilege</code> enabled. Alternatively, a print processor can be registered to the print spooler service by adding the <code>HKLM\SYSTEM\\[CurrentControlSet or ControlSet001]\Control\Print\Environments\\[Windows architecture: e.g., Windows x64]\Print Processors\\[user defined]\Driver</code> 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 <code>GetPrintProcessorDirectory</code> API call, or referenced via a relative path from this directory.² After the print processors are installed, the print spooler service, which starts during boot, must be restarted in order for them to run.³ The print spooler service runs under SYSTEM level permissions; therefore, print processors installed by an adversary may run under elevated privileges.

1. Microsoft Intro Print Processors
2. Microsoft AddPrintProcessor May 2018
3. ESET PipeMon May 2020

Groups using this technique

Claims

No public claim points at this technique yet.

Auto-ingested and not human-reviewed; confidence and validity read by citation.