kryptor6

Hunt Hypothesis

This hypothesis targets the presence of the Kryptor6 malware family, a known ransomware strain that often leverages obfuscated payloads to encrypt files and establish persistence on compromised hosts. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify early-stage infections or dormant backdoors before they progress to active encryption or lateral movement within the cloud environment.

YARA Rule

rule kryptor6
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 03 [3] E9 EB 68 58 33 D2 74 02 E9 E9 40 42 75 02 }

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 DevOps engineer executes a custom Python script using pyinstaller to create a standalone executable for a CI/CD pipeline tool, where the resulting binary contains a specific header pattern or string that matches the kryptor6 heuristic.
  • Filter/Exclusion: Exclude processes where the parent process is python.exe or pip.exe and the file path resides in a known build directory (e.g., C:\builds\ or C:\artifacts\).
• Scenario: An IT administrator runs 7z.exe (7-Zip) to extract a large archive containing mixed file types, and the YARA rule triggers on a specific embedded resource or metadata field within the extracted files that coincidentally matches the kryptor6 signature.
  • Filter/Exclusion: Exclude alerts where the file extension is .7z, .zip, or .rar and the process name is 7z.exe, WinRAR.exe, or tar.exe.
• Scenario: A security team performs a routine vulnerability scan using Nessus or Qualys, which spawns temporary worker processes that write small configuration or state files to disk; these files contain a specific GUID or version string that overlaps with the kryptor6 pattern.
  • Filter/Exclusion: Exclude files located in standard scanner temp directories (e.g., C:\ProgramData\Tenable\Nessus\ or C:\Program Files\Qualys\) and processes with names like nessusd.exe or qagent.exe.
• Scenario: A developer uses Visual Studio Code with the C/C++ extension to compile a small C++ utility, and the generated .obj or intermediate .pdb file contains a specific compiler banner or debug section that matches the rule’s byte sequence.