PureBasic4xDLLNeilHodgson

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging custom or obfuscated PureBasic-compiled DLLs to execute stealthy code injection and persistence mechanisms within the environment. Proactive hunting for this signature in Azure Sentinel is essential because standard detection rules often miss niche compiler artifacts that can serve as a covert entry point for advanced threats evading traditional heuristic analysis.

YARA Rule

rule PureBasic4xDLLNeilHodgson
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 83 7C 24 08 01 75 0E 8B 44 24 04 A3 [3] 10 E8 22 00 00 00 83 7C 24 08 02 75 00 83 7C 24 08 00 75 05 E8 ?? 00 00 00 83 7C 24 08 03 75 00 B8 01 00 00 00 C2 0C 00 68 00 00 00 00 68 00 10 00 00 68 00 00 00 00 E8 ?? 0F 00 00 A3 }

condition:
		$a0 at pe.entry_point
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the PureBasic4xDLLNeilHodgson detection rule, along with targeted filters or exclusions:

• Scenario: Automated Deployment via Microsoft Endpoint Configuration Manager (SCCM)

  • Context: The SCCM client service (ccmexec.exe) frequently extracts and loads custom PureBasic-based deployment agents or DLLs during scheduled maintenance windows to push software updates. These artifacts often match the signature of the rule but are part of a trusted, signed enterprise workflow.
  • Filter/Exclusion: Create an exclusion based on the parent process name ccmexec.exe and restrict the scope to specific file paths within the SCCM installation directory (e.g., C:\Program Files\Microsoft Configuration Manager).

• Scenario: Legacy Reporting Tool Execution via Task Scheduler

  • Context: A legacy internal reporting application, built using PureBasic for rapid prototyping, runs nightly via a Windows Scheduled Task (taskschd.exe). The task launches the executable which dynamically loads a DLL containing custom business logic that triggers this detection.
  • Filter/Exclusion: Exclude processes where the parent is svchost.exe (specifically the Schedule service group) or filter by the specific scheduled task name (e.g., \Microsoft\Windows\TaskScheduler\LegacyReportEngine) and the file hash of the known good DLL.

• Scenario: Development Environment Compilation in Visual Studio

  • Context: Internal developers compiling PureBasic projects within Visual Studio (devenv.exe or msbuild.exe) generate temporary DLLs during the build process. The YARA rule may flag these intermediate compilation artifacts as suspicious activity, even though they are transient and expected in a dev environment.
  • Filter/Exclusion: Apply an exclusion for processes running within specific development directories (e.g., `C:\