KGBSFX

Hunt Hypothesis

This rule detects the presence of the KGBSFX YARA signature, which typically identifies specific malware families or suspicious code patterns associated with known threat actors. Proactively hunting for this indicator in Azure Sentinel allows the SOC team to identify compromised endpoints or staging environments before they progress to more advanced post-exploitation activities.

YARA Rule

rule KGBSFX
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 BE 00 A0 46 00 8D BE 00 70 F9 FF 57 83 CD FF EB 10 90 90 90 90 90 90 8A 06 46 88 07 47 01 DB 75 07 8B 1E 83 EE FC 11 DB 72 ED B8 01 00 00 00 01 DB 75 07 8B 1E 83 EE FC 11 DB 11 C0 01 DB 73 }

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 DevOps engineer uses a legitimate open-source Go-based tool (such as gops, pprof, or a custom internal microservice) that embeds the specific byte sequence or string pattern targeted by the KGBSFX YARA rule. Since YARA rules often match on static strings or specific function signatures, standard Go binaries compiled with certain optimization flags or containing specific dependency libraries may inadvertently match the signature.

  • Filter/Exclusion: Exclude processes where the parent process is a known build tool (e.g., go.exe, msbuild.exe, dotnet.exe) or where the executable path resides in standard development directories (e.g., C:\Users\<User>\go\bin\, C:\Program Files\Go\bin\). Additionally, verify if the binary is signed by a trusted internal CA or known vendor.

• Scenario: An enterprise backup or data migration job (using tools like Veeam, Commvault, or Rclone) temporarily copies or stages a large binary file (e.g., a database dump, a container image layer, or a compressed archive) into a temporary directory (%TEMP% or C:\Temp). If the YARA rule matches on a common library signature (like a specific version of libcrypto or a Go runtime segment) that is frequently embedded in these archives, the temporary file will trigger the alert during the copy or extraction phase.

  • Filter/Exclusion: Exclude files located in standard temporary paths (%TEMP%, C:\Temp, C:\Windows\Temp) if the parent process is a known backup or file transfer utility (e.g., rclone.exe, vssadmin.exe, wbadmin.exe). Ensure the exclusion applies only to read/write operations and not to execution from these paths.

• Scenario: A scheduled PowerShell or