Detect Print Processors in Google Chronicle
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 a Registry key under HKLM\SYSTEM\CurrentControlSet\Control\Print\Environments\Windows x64\Print Processors with a Driver value pointing to the malicious DLL. The print spooler service runs under SYSTEM level permissions, therefore print processors installed by an adversary may run under elevated privileges.
MITRE ATT&CK
- Tactic
- Persistence Privilege Escalation
- Technique
- T1547 Boot or Logon Autostart Execution
- Sub-technique
- T1547.012 Print Processors
- Canonical reference
- https://attack.mitre.org/techniques/T1547/012/
YARA-L Detection Query
rule t1547_012_print_processor_abuse {
meta:
author = "Argus Detection Engineering"
description = "Detects T1547.012 - Print Processor abuse for persistence and privilege escalation via registry modification, DLL drops in spool directory, or suspicious spoolsv.exe child processes"
severity = "HIGH"
mitre_attack_technique = "T1547.012"
mitre_attack_tactic = "Persistence, Privilege Escalation"
reference = "https://attack.mitre.org/techniques/T1547/012/"
created = "2026-04-20"
events:
(
// Signal 1: Registry modification to Print Processors path
(
$e.metadata.event_type = "REGISTRY_MODIFICATION"
and re.regex($e.target.registry.registry_key, `(?i)Control\\Print\\Environments.*Print Processors`)
)
or
// Signal 2: DLL created in print processor spool directory
(
$e.metadata.event_type = "FILE_CREATION"
and re.regex($e.target.file.full_path, `(?i)\\spool\\prtprocs\\.*\.dll$`)
)
or
// Signal 3: Unexpected child process from spoolsv.exe
(
$e.metadata.event_type = "PROCESS_LAUNCH"
and $e.principal.process.file.full_path = /(?i)spoolsv\.exe$/
and not $e.target.process.file.full_path = /(?i)(splwow64|PrintIsolationHost|printfilterpipelinesvc|conhost)\.exe$/
)
)
condition:
$e
}Chronicle YARA-L 2.0 rule detecting T1547.012 Print Processor persistence through three distinct UDM event patterns: registry modifications targeting the Windows Print Processor registry path, file creation of DLLs in the print spooler processor directory, and anomalous process launches where spoolsv.exe is the parent. The print spooler runs under SYSTEM, making this a critical privilege escalation path.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate OEM printer driver installations from vendors such as HP, Canon, or Xerox that include custom print processors registered during driver setup
- Enterprise print management platforms (PaperCut MF, Pharos, uniFLOW) that deploy proprietary print processor DLLs across managed endpoints
- Windows servicing operations during OS updates that modify or recreate print processor registry entries as part of component store servicing
Other platforms for T1547.012
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Print Processor Registry Key Creation
Expected signal: Sysmon Event ID 12: Registry Key Created for TestProcessor_df00tech subkey. Sysmon Event ID 13: Registry Value Set for Driver value with Details=winprint.dll. Security Event ID 4688 with CommandLine containing reg add and the full registry path.
- Test 2DLL Drop in Print Processor Directory
Expected signal: Sysmon Event ID 11: File Create with TargetFilename=C:\Windows\System32\spool\prtprocs\x64\df00tech_test_printproc.dll, Image=cmd.exe. DeviceFileEvents with ActionType=FileCreated in the prtprocs directory.
- Test 3PowerShell Print Processor Registration (Earth Lusca Style)
Expected signal: Sysmon Event ID 1: Process Create for powershell.exe with full command line. Sysmon Event ID 12: Registry Key Created. Sysmon Event ID 13: Registry Value Set. PowerShell ScriptBlock Log Event ID 4104 capturing the registry manipulation.
- Test 4Enumerate Existing Print Processors for Reconnaissance
Expected signal: Sysmon Event ID 1: Process Create for reg.exe with CommandLine containing reg query and Print Processors path. Security Event ID 4688 with same details. No registry modification events (read-only operation).
References (7)
- https://attack.mitre.org/techniques/T1547/012/
- https://docs.microsoft.com/en-us/windows/win32/printdocs/addprintprocessor
- https://learn.microsoft.com/windows-hardware/drivers/print/introduction-to-print-processors
- https://www.welivesecurity.com/2020/05/21/no-game-over-winnti-group/
- https://www.trendmicro.com/en_us/research/22/a/earth-lusca-employs-sophisticated-infrastructure-varied-tools-and-techniques.html
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1547.012/T1547.012.md
- https://github.com/SigmaHQ/sigma/tree/master/rules/windows/registry/registry_set
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