PassCV Malware mentioned in Cylance Report

Hunt Hypothesis

PassCV malware is likely being used by adversaries to establish persistence and exfiltrate data through compromised Azure environments. SOC teams should proactively hunt for this behavior to identify and mitigate potential long-term data breaches and lateral movement in their cloud infrastructure.

YARA Rule

rule PassCV_Sabre_Malware_1 
{

   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 = "24a9bfbff81615a42e42755711c8d04f359f3bf815fb338022edca860ff1908a"
      hash2 = "e61e56b8f2666b9e605127b4fcc7dc23871c1ae25aa0a4ea23b48c9de35d5f55"

   strings:
      $x1 = "F:\\Excalibur\\Excalibur\\Excalibur\\" ascii
      $x2 = "bin\\oSaberSvc.pdb" ascii
      $s1 = "cmd.exe /c MD " fullword ascii
      $s2 = "https://www.baidu.com/s?ie=utf-8&f=8&rsv_bp=0&rsv_idx=1&tn=baidu&wd=ip138" fullword wide
      $s3 = "CloudRun.exe" fullword wide
      $s4 = "SaberSvcB.exe" fullword wide
      $s5 = "SaberSvc.exe" fullword wide
      $s6 = "SaberSvcW.exe" fullword wide
      $s7 = "tianshiyed@iaomaomark1#23mark123tokenmarkqwebjiuga664115" fullword wide
      $s8 = "Internet Connect Failed!" fullword ascii

   condition:
      ( uint16(0) == 0x5a4d and filesize < 1000KB and ( 1 of ($x*) and 5 of ($s*) ) ) or ( all of them )
}

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 10 string patterns in its detection logic.

References

False Positive Guidance

Scenario: A system administrator is using PassCV as part of a legitimate security toolchain to analyze malware samples.
Filter/Exclusion: Exclude processes where the parent process is a known security tool (e.g., CylanceProtect.exe, ProcessMonitor.exe, or Procmon.exe).
Scenario: A scheduled job runs PassCV to scan for malware in a sandboxed environment for threat intelligence purposes.
Filter/Exclusion: Exclude processes running from a known sandbox or virtualization directory (e.g., C:\Windows\System32\vmtools, C:\Program Files (x86)\Sandboxie, or C:\Users\Public\Temp).
Scenario: A system update or patching task triggers a script that temporarily uses PassCV to verify the integrity of system files.
Filter/Exclusion: Exclude processes initiated by a known patching tool (e.g., WindowsUpdate.exe, msiexec.exe, or setup.exe).
Scenario: A developer is using PassCV to test a custom malware analysis tool or script in a controlled development environment.
Filter/Exclusion: Exclude processes running from a development directory (e.g., C:\Dev\Tools, C:\Users\DevUser\Projects, or C:\Code) or where the user is a developer with elevated privileges.
Scenario: A backup or archive tool uses PassCV to scan files during a scheduled backup operation.
Filter/Exclusion: Exclude processes associated with backup software (e.g., VeeamBackup.exe, AcronisTrueImage.exe, or wbadmin.exe) or running from a backup directory (e.g., C:\Backup, D:\Archives).