PureBasic

Hunt Hypothesis

This rule identifies the presence of PureBasic, a lightweight interpreted language often used by threat actors to create compact, obfuscated payloads or downloaders that may evade traditional static analysis. Proactively hunting for this indicator in Azure Sentinel allows the SOC to detect potential footholds or staging activities where adversaries leverage this niche toolchain to execute malicious code or establish persistence before triggering more complex behavioral alerts.

YARA Rule

rule PureBasic : Neil Hodgson
{
      	meta:
		author="_pusher_"
		date="2016-07"
	strings:
		//make check for msvrt.dll
		$c0 = { 55 8B EC 6A 00 68 00 10 00 00 6A ?? FF 15 ?? ?? ?? ?? A3 ?? ?? ?? ?? C7 05 ?? ?? ?? ?? 00 00 00 00 C7 05 ?? ?? ?? ?? 10 00 00 00 A1 ?? ?? ?? ?? 50 6A ?? 8B 0D ?? ?? ?? ?? 51 FF 15 ?? ?? ?? ?? A3 ?? ?? ?? ?? 5D C3 CC CC CC CC CC CC CC CC CC }
		$c1 = { 68 ?? ?? 00 00 68 00 00 00 00 68 ?? ?? ?? 00 E8 ?? ?? ?? 00 83 C4 0C 68 00 00 00 00 E8 ?? ?? ?? 00 A3 ?? ?? ?? 00 68 00 00 00 00 68 00 10 00 00 68 00 00 00 00 E8 ?? ?? ?? 00 A3 }
		$aa0 = "\x00MSVCRT.dll\x00" ascii
		$aa1 = "\x00CRTDLL.dll\x00" ascii
	condition:
		(for any of ($c0,$c1) : ( $ at pe.entry_point  )) and 
		(any of ($aa*) ) and
		((pe.linker_version.major == 2) and (pe.linker_version.minor == 50 ))
}

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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Legacy Internal Tooling Maintenance: Developers or system administrators maintaining custom internal utilities written in PureBasic (often used for lightweight GUI tools or system diagnostics on Windows) may compile or execute .exe files that match the YARA signature. Filter/Exclusion: Exclude files located in specific development directories (e.g., C:\Dev\PureBasicProjects\) or processes spawned by known IDEs like PBIDE.exe or CodeBlocks.exe.
• Automated Backup or Cleanup Scripts: Scheduled tasks (Task Scheduler) that run custom PureBasic-based scripts to clean temporary files, rotate logs, or perform disk maintenance in legacy server environments. Filter/Exclusion: Exclude processes where the parent process is svchost.exe (specifically the Task Scheduler service) and the executable path resides in a known service directory (e.g., C:\Program Files\InternalTools\ or C:\Scripts\).
• Third-Party Application Components: Some older or niche third-party applications (e.g., specialized media converters, small utility suites, or legacy POS systems) may bundle PureBasic-compiled helper executables for specific sub-tasks. Filter/Exclusion: Exclude executables whose parent process is a known third-party application binary (e.g., MediaConverter.exe, LegacyPOS.exe) and where the file hash or path matches a verified allowlist of known-good binaries.
• CI/CD Build Artifacts: Continuous Integration pipelines that build or test legacy components may temporarily extract or execute PureBasic-compiled test binaries in build agent directories. Filter/Exclusion: Exclude files located in standard CI/CD workspace directories (e.g., C:\agent\work\, D:\Jenkins\workspace\) or processes spawned by build agents like jenkins.exe or vstsagent.exe.
• Legacy Driver or Firmware Update Utilities: Vendor-provided update