SimbiOZExtranger

Hunt Hypothesis

This YARA rule targets the SimbiOZExtranger malware, a known threat often associated with web-based attacks and credential theft, allowing analysts to identify compromised hosts before lateral movement occurs. Proactively hunting for this signature in Azure Sentinel is critical to detect low-severity intrusions that may evade standard behavioral detections and establish a foothold within the environment.

YARA Rule

rule SimbiOZExtranger
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 60 E8 00 00 00 00 5D 81 ED 07 10 40 00 68 80 0B 00 00 8D 85 1F 10 40 00 50 E8 84 0B 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 DevOps engineer uses a legitimate open-source tool or custom script that embeds the specific byte sequence or string pattern targeted by the SimbiOZExtranger YARA rule (e.g., a specific library header, magic number, or debug string) within a compiled binary or script.

  • Filter/Exclusion: Exclude files located in known development directories (e.g., C:\dev\, C:\src\, C:\projects\) or exclude binaries owned by specific service accounts (e.g., svc-build, dev-team) if the rule targets code artifacts rather than memory.

• Scenario: A scheduled maintenance job runs a third-party utility (e.g., a disk cleaner, log rotator, or backup agent like Veeam or Commvault) that temporarily creates a temporary file or memory region matching the YARA pattern during its operation.

  • Filter/Exclusion: Exclude processes running from standard vendor installation paths (e.g., C:\Program Files\Veeam\, C:\Program Files\Commvault\) or exclude files in temporary directories (%TEMP%, C:\Windows\Temp\) if the detection is file-based.

• Scenario: An administrator manually copies a known-good application installer or patch package to a shared network drive or local admin share for distribution, and the YARA rule matches the installer’s embedded metadata or signature.

  • Filter/Exclusion: Exclude files with specific extensions (.msi, .exe, .zip) located in admin shares (e.g., \\fileserver\share$\, C:\AdminShare\) or exclude files modified within the last 24 hours if the rule is time-sensitive.

• Scenario: A custom internal tool or wrapper script (e.g., a PowerShell or Python script) contains a hardcoded string or