FSGv110EngdulekxtBorlandDelphiMicrosoftVisualC

Hunt Hypothesis

This hypothesis targets the presence of executable files compiled with Borland Delphi or Microsoft Visual C++ that exhibit specific structural characteristics, potentially indicating the use of custom or obfuscated malware binaries in the environment. Proactively hunting for these artifacts allows the SOC to identify low-severity, potentially stealthy threats that may evade standard signature-based detections by leveraging common development frameworks for code execution.

YARA Rule

rule FSGv110EngdulekxtBorlandDelphiMicrosoftVisualC
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 1B DB E8 02 00 00 00 1A 0D 5B 68 80 [2] 00 E8 01 00 00 00 EA 5A 58 EB 02 CD 20 68 F4 00 00 00 EB 02 CD 20 5E 0F B6 D0 80 CA 5C 8B 38 EB 01 35 EB 02 DC 97 81 EF F7 65 17 43 E8 02 00 00 00 97 CB 5B 81 C7 B2 8B A1 0C 8B D1 83 EF 17 EB 02 0C 65 83 EF 43 13 }
	$a1 = { C1 C8 10 EB 01 0F BF 03 74 66 77 C1 E9 1D 68 83 [2] 77 EB 02 CD 20 5E EB 02 CD 20 2B F7 }

condition:
		$a0 at pe.entry_point or $a1 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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A legacy internal business application (e.g., InventoryManager.exe) compiled with Borland Delphi 7 is deployed via Group Policy to user workstations. The YARA rule matches the specific compiler signature and string patterns embedded in the binary, triggering an alert on every machine where the application is installed or executed.
  • Filter/Exclusion: Exclude files located in the specific application directory (e.g., C:\Program Files\LegacyApps\InventoryManager\) or add a hash-based exclusion for the known good SHA256 of the executable.
• Scenario: An IT administrator runs a standard Microsoft Visual C++ Redistributable installer (vc_redist.x64.exe) during a scheduled patching cycle using a tool like PDQ Deploy or SCCM. The installer binary, while primarily VC++, may contain embedded Delphi-based helper utilities or share common compiler artifacts that satisfy the YARA rule’s conditions, causing a false positive during routine maintenance.
  • Filter/Exclusion: Exclude processes initiated by known deployment services (e.g., PDQDeployService.exe, SCCMClient.exe) or exclude files matching the specific version string of the VC++ Redistributable package in the file path or metadata.
• Scenario: A developer on the R&D team compiles a test utility using a mixed-toolchain approach, linking a Borland Delphi module with a Microsoft Visual C++ wrapper. The resulting hybrid binary (TestHarness.exe) resides in a local development folder (C:\Users\<dev>\Projects\) and is executed for local testing, triggering the rule due to the presence of both compiler signatures.
  • Filter/Exclusion: Exclude files located under user profile directories (e.g., C:\Users\*) or specific development workspace paths (e.g., *\Projects\, *\Workspace\) to avoid alerting on local development