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T1547.012: 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.

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. After the print processors are installed, the print spooler service, which starts during boot, must be restarted in order for them to run.

The print spooler service runs under SYSTEM level permissions, therefore print processors installed by an adversary may run under elevated privileges.

Positive Technologies products that cover the technique

Description of detection methods is not available yet

Detection

IDDS0011Data source and componentModule: Module LoadDescription

Monitor for abnormal DLLs that are loaded by spoolsv.exe. Print processors that do not correlate with known good software or patching may be suspicious. New print processor DLLs are written to the print processor directory.

IDDS0027Data source and componentDriver: Driver LoadDescription

Monitor for unusual kernel driver installation activity that may abuse print processors to run malicious DLLs during system boot for persistence and/or privilege escalation.

IDDS0009Data source and componentProcess: OS API ExecutionDescription

Monitor process API calls to AddPrintProcessor and GetPrintProcessorDirectory.

IDDS0024Data source and componentWindows Registry: Windows Registry Key ModificationDescription

Monitor Registry writes to HKLM\SYSTEM\ControlSet001\Control\Print\Environments\[Windows architecture]\Print Processors\[user defined]\Driver or HKLM\SYSTEM\CurrentControlSet\Control\Print\Environments\[Windows architecture]\Print Processors\[user defined]\Driver as they pertain to print processor installations.

IDDS0022Data source and componentFile: File CreationDescription

Monitor for newly constructed files that may abuse print processors to run malicious DLLs during system boot for persistence and/or privilege escalation.

Mitigation

IDM1018NameUser Account ManagementDescription

Limit user accounts that can load or unload device drivers by disabling SeLoadDriverPrivilege.