WARNINGTROJANRobinPE

Hunt Hypothesis

This rule identifies the presence of the RobinPE trojan, a malicious executable often used for initial access or persistence that may evade standard signature-based detections. Proactively hunting for this specific YARA signature allows the SOC team to uncover dormant or low-severity threats that could be leveraged for lateral movement or data exfiltration within the Azure environment.

YARA Rule

rule WARNINGTROJANRobinPE
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 6A 00 6A 20 6A 02 6A 00 6A 03 68 00 00 00 }

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

• Scenario: A developer or system administrator uses a PE packing tool (such as UPX, ASPack, or Themida) to compress or protect a custom internal utility or a third-party plugin before deployment. The WARNINGTROJANRobinPE rule often triggers on specific header patterns, section names, or entropy levels associated with packed executables, mistaking the compressed code structure for a known trojan signature.

  • Filter/Exclusion: Exclude files located in specific development or staging directories (e.g., C:\Dev\, C:\Staging\) or exclude processes where the parent process is a known build tool (e.g., msbuild.exe, dotnet.exe, cmake.exe). Additionally, consider whitelisting specific hash values of known packed internal tools.

• Scenario: A legacy line-of-business application or a specific vendor-provided agent (e.g., a hardware monitoring tool or a niche backup client) is updated via a scheduled task or service. The update process involves writing a new PE file that has been signed but retains specific section alignments or import table characteristics that match the WARNINGTROJANRobinPE heuristic. This is common with older C/C++ applications that do not use modern linking standards.

  • Filter/Exclusion: Exclude files that are digitally signed by a trusted internal CA or known vendor (e.g., Microsoft, VMware, Veeam) and located in standard vendor installation paths (e.g., C:\Program Files\VendorName\). You can also filter based on the presence of a valid Authenticode signature and a specific Signer field.

• Scenario: A CI/CD pipeline or automated deployment script executes a small, self-contained PE executable (often a Go or Rust binary compiled for Windows) that is used for configuration management or log rotation. These binaries may have high entropy or unusual section names