kryptor9

Hunt Hypothesis

This hypothesis targets the execution of the Kryptor9 malware family, a known threat actor tool often used for initial access or lateral movement via PowerShell or script-based payloads. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify compromised endpoints before the malware establishes persistence or exfiltrates data, leveraging YARA scanning capabilities to catch low-severity threats that may evade traditional signature-based detections.

YARA Rule

rule kryptor9
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 [4] 5E B9 [4] 2B C0 02 04 0E D3 C0 49 79 F8 41 8D 7E 2C 33 46 ?? 66 B9 }

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 encryption utility (e.g., GPG, OpenSSL, or a custom internal tool named kryptor) to encrypt sensitive configuration files or secrets before committing them to a repository or uploading them to a secure storage bucket.

  • Filter/Exclusion: Exclude processes where the parent process is a known version control client (e.g., git.exe, svn.exe) or a CI/CD agent (e.g., jenkins-agent.exe, gitlab-runner.exe), or exclude file paths under specific development directories (e.g., C:\dev\, D:\projects\) if the rule triggers on file creation/modification.

• Scenario: An IT administrator runs a scheduled PowerShell script or batch job to encrypt backup archives (e.g., .zip or .tar.gz files) using a custom encryption wrapper script that invokes a binary or DLL with a name matching the YARA signature (e.g., kryptor9.dll or kryptor.exe) as part of a nightly backup encryption routine.

  • Filter/Exclusion: Exclude executions where the command line contains keywords like backup, encrypt, or archive, or exclude processes spawned by Task Scheduler (svchost.exe with specific service names) or cron-like schedulers on Linux/WSL environments.

• Scenario: A security team performs a periodic vulnerability scan or integrity check using a tool that bundles a lightweight encryption module for hashing or encrypting scan results, where the module’s binary name or internal string matches the YARA pattern kryptor9.

  • Filter/Exclusion: Exclude processes where the parent process is a known security scanner (e.g., nmap.exe, qualys_agent.exe, tenable_agent.exe) or where the working