Auto-generated rule - file b5ef16922e2c76b09edd71471dd837e89811c5e658406a8495c1364d0d9dc690

Hunt Hypothesis

This detection rule identifies anomalous file creation events that may indicate early-stage adversary activity, such as malware deployment or data staging, within the Azure environment. Proactive hunting for these specific file artifacts is essential to uncover silent threats that bypass standard alerting thresholds and to establish a baseline of normal file system behavior before an incident escalates.

YARA Rule

rule GoldenEyeRansomware_Dropper_MalformedZoomit {
   meta:
      description = "Auto-generated rule - file b5ef16922e2c76b09edd71471dd837e89811c5e658406a8495c1364d0d9dc690"
      author = "Florian Roth"
      reference = "https://goo.gl/jp2SkT"
      date = "2016-12-06"
      hash1 = "b5ef16922e2c76b09edd71471dd837e89811c5e658406a8495c1364d0d9dc690"
   strings:
      $s1 = "ZoomIt - Sysinternals: www.sysinternals.com" fullword ascii
      $n1 = "Mark Russinovich" wide
   condition:
      ( uint16(0) == 0x5a4d and filesize < 800KB and $s1 and not $n1 )
}

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.

References

• https://goo.gl/jp2SkT
• Source Rule

False Positive Guidance

Based on the rule title and hash provided, this detection appears to monitor file system activity (likely creation, modification, or execution) of files with specific cryptographic signatures or in sensitive directories. In an enterprise environment, legitimate administrative actions often mimic suspicious file behavior.

Here are 4 specific false positive scenarios with corresponding filters:

• Antivirus and EDR Real-Time Scanning Artifacts

  • Scenario: Endpoint Detection and Response (EDR) agents like CrowdStrike Falcon, Microsoft Defender for Endpoint, or SentinelOne frequently create temporary quarantine files, update signature databases, or generate log artifacts in protected directories (e.g., C:\ProgramData\Antivirus or %TEMP%). These operations often involve writing files with high entropy that match the rule’s hash pattern.
  • Suggested Filter: Exclude file paths containing known EDR installation directories and exclude processes running under the context of the specific security vendor (e.g., ImageName: C:\Program Files\CrowdStrike\csagent.exe). Additionally, filter out files with extensions commonly used for temporary quarantine storage (e.g., .tmp, .qar).

• Scheduled System Patching and Software Updates

  • Scenario: Automated patch management tools such as Microsoft WSUS, Ivanti Neurons, or SCCM (Configuration Manager) routinely download update packages, extract binaries, and write configuration files to system folders during maintenance windows. These activities generate a high volume of file creation events with consistent hashes that may trigger the rule if it monitors for “new” or “unfamiliar” file patterns in critical paths like C:\Windows\SoftwareDistribution.
  • Suggested Filter: Create an exclusion based on the parent process name (e.g., TrustedInstaller, ccmexec.exe) and restrict the alert to specific time windows defined by maintenance schedules. Alternatively