PassCV Malware mentioned in Cylance Report

Hunt Hypothesis

PassCV malware is likely being used by adversaries to execute arbitrary code and maintain persistence within a network. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential compromise from low-severity, yet potentially stealthy malware activity.

YARA Rule

rule PassCV_Sabre_Malware_3 
{

   meta:
      description = "PassCV Malware mentioned in Cylance Report"
      author = "Florian Roth"
      reference = "https://blog.cylance.com/digitally-signed-malware-targeting-gaming-companies"
      date = "2016-10-20"
      hash1 = "28c7575b2368a9b58d0d1bf22257c4811bd3c212bd606afc7e65904041c29ce1"

   strings:
      $x1 = "NXKILL" fullword wide
      $s1 = "2OLE32.DLL" fullword ascii
      $s2 = "localspn.dll" fullword wide
      $s3 = "!This is a Win32 program." fullword ascii
   
   condition:
      ( uint16(0) == 0x5a4d and filesize < 8000KB and $x1 and 2 of ($s*) )
}

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 4 string patterns in its detection logic.

References

• https://blog.cylance.com/digitally-signed-malware-targeting-gaming-companies
• Source Rule

False Positive Guidance

• Scenario: A system administrator is running a scheduled job to update the Cylance endpoint protection software using the cyUpdate tool.
  Filter/Exclusion: Exclude processes associated with the cyUpdate executable or any process initiated by the Cylance service account.

• Scenario: A security analyst is manually reviewing logs using the logparser tool to investigate a potential security incident.
  Filter/Exclusion: Exclude processes initiated by the logparser tool or any process with a user context of a security analysis team member.

• Scenario: A database administrator is executing a SQL backup job using sqlbackup.exe that includes a script referencing a file named PassCV.exe as part of a legacy system cleanup.
  Filter/Exclusion: Exclude processes initiated by the SQL backup service or any process involving the sqlbackup.exe executable.

• Scenario: A DevOps engineer is deploying a containerized application using Docker, and the Dockerfile includes a placeholder named PassCV for a future module.
  Filter/Exclusion: Exclude processes related to Docker builds or any process initiated by the DevOps CI/CD pipeline.

• Scenario: An IT technician is performing a system cleanup and manually deletes a file named PassCV.exe that was previously used for a legitimate diagnostic tool.
  Filter/Exclusion: Exclude processes initiated by the IT technician’s user account or any process involving file deletion operations on known legitimate diagnostic tools.