Detect Print Processors in Sumo Logic CSE
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/
Sumo Detection Query
(_sourceCategory="windows/sysmon" OR _sourceCategory="windows/events")
| json auto
| where EventID in ("1", "11", "12", "13", "14")
| if (EventID == "13" OR EventID == "12",
if (TargetObject matches "*Control\\Print\\Environments*Print Processors*", "registry_hit", "no_match"),
if (EventID == "11",
if (TargetFilename matches "*\\spool\\prtprocs\\*.dll", "file_hit", "no_match"),
if (EventID == "1",
if (ParentImage matches "*\\spoolsv.exe"
AND !(Image matches "*\\splwow64.exe")
AND !(Image matches "*\\PrintIsolationHost.exe")
AND !(Image matches "*\\printfilterpipelinesvc.exe")
AND !(Image matches "*\\conhost.exe"),
"process_hit", "no_match"),
"no_match"))) as detection_type
| where detection_type != "no_match"
| eval dll_known = if (TargetObject matches "*(winprint|filterpipelineprintproc).dll*", "true", "false")
| eval processor_name = if (EventID == "13", replace(TargetObject, ".*Print Processors\\\\(.+?)\\\\.*", "$1"), "N/A")
| fields _messageTime, Computer, User, EventID, detection_type, TargetObject, Details, TargetFilename, Image, ParentImage, CommandLine, dll_known, processor_name
| sort by _messageTime descDetects T1547.012 Print Processor persistence in Sumo Logic by parsing Sysmon events for three behavioral indicators: registry key creation/modification under the Print Processors path (EventID 12/13), DLL file drops into the print spooler directory (EventID 11), and anomalous child processes launched by spoolsv.exe (EventID 1). Enriches results with known-DLL classification and extracted processor name.
Data Sources
Required Tables
False Positives & Tuning
- Enterprise print server deployments may routinely install custom print processors as part of managed print service contracts
- Print monitoring or auditing software may create DLLs in the prtprocs directory during initial setup
- Windows printer compatibility layer (splwow64.exe) interactions during 32-bit application print jobs from spoolsv.exe may produce false alerts if filter list is incomplete
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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