{
  "family": "cmy3u",
  "sample_count": 16,
  "category": "ransomware",
  "description": "Cmy3u (classified across security vendors as Ransom:Win32/Cmy3u, Trojan-Ransom.Win32.Cmy3u, and Win32/Cmy3u) is a targeted crypto-ransomware family engineered to rapidly compromise and encrypt Windows client workstations and file servers. Distributed via spear-phishing emails containing weaponized office documents, malicious downloader scripts, and credential abuse over exposed Remote Desktop Protocol (RDP) connections, Cmy3u establishes execution privileges before initiating local and network storage discovery. The ransomware scans all attached fixed, removable, and SMB network drives, targeting enterprise documents, databases, system backups, and virtual machine disk images while selectively skipping core Windows operating system files to keep the system bootable. It uses AES-256 symmetric encryption to lock files and appends custom extensions, generating ransom instructions in text and HTML formats directing victims to contact threat actors via Tor-hosted negotiation panels. Furthermore, Cmy3u executes administrative shell commands to delete Volume Shadow Copies and disable automated startup repair.",
  "cta": "Published by the SystemHelpdesk Threat Intelligence Team.",
  "aliases": [
    "Ransom:Win32/Cmy3u",
    "Trojan-Ransom.Win32.Cmy3u",
    "Win32/Cmy3u",
    "Cmy3u Ransomware",
    "Ransom.Cmy3u"
  ],
  "enrichment_level": "curated_sourced",
  "faq": [
    {
      "@type": "Question",
      "name": "What is Ransom:Win32/Cmy3u?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Cmy3u is a crypto-ransomware family that encrypts files on Windows workstations and servers using AES-256."
      }
    },
    {
      "@type": "Question",
      "name": "How does Cmy3u target network resources?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "It enumerates mapped network drives and SMB shares, recursively encrypting shared files across the corporate network."
      }
    },
    {
      "@type": "Question",
      "name": "How does Cmy3u prevent file recovery via Windows features?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "It executes vssadmin commands to purge Volume Shadow Copies and uses bcdedit to disable system startup recovery."
      }
    },
    {
      "@type": "Question",
      "name": "What vector is commonly used to distribute Cmy3u?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Spear-phishing emails with malicious attachments, RDP credential brute-forcing, and multi-stage trojan loaders."
      }
    },
    {
      "@type": "Question",
      "name": "What steps should be taken upon detecting a Cmy3u infection?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Isolate affected systems from the network, preserve ransom notes and memory dumps, and restore data from isolated offline backups."
      }
    }
  ],
  "faq_count": 5,
  "mitre_attack": [
    "T1486",
    "T1490",
    "T1083",
    "T1135",
    "T1059.003",
    "T1070.004"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-10-15",
  "mitre_attack_detail": [
    {
      "id": "T1105",
      "name": "Ingress Tool Transfer",
      "tactic": "Command and Control"
    },
    {
      "id": "T1055",
      "name": "Process Injection",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1547.001",
      "name": "Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder",
      "tactic": "Persistence"
    },
    {
      "id": "T1566.001",
      "name": "Phishing: Spearphishing Attachment",
      "tactic": "Initial Access"
    },
    {
      "id": "T1027",
      "name": "Obfuscated Files or Information",
      "tactic": "Defense Evasion"
    }
  ],
  "containment_steps": [
    "Isolate the endpoint immediately to prevent Cmy3u from downloading and executing its secondary payloads (e.g., ransomware).",
    "Audit the Windows Task Scheduler and Registry Run keys to identify and remove the Cmy3u persistence mechanisms.",
    "Review firewall and proxy logs to identify the C2 domains Cmy3u attempted to contact, and block them enterprise-wide.",
    "Capture a live memory image (RAM dump) to extract the injected Cmy3u modules and identify the secondary payloads."
  ],
  "what_to_avoid": [
    "Do not close an incident simply because the initial Cmy3u dropper was quarantined; always verify if secondary payloads were downloaded.",
    "Avoid relying solely on manual file deletion, as the injected processes will likely just recreate the dropped binaries."
  ],
  "target_industries": [
    "Healthcare",
    "Critical Infrastructure",
    "Enterprise"
  ],
  "motivation": "Financial Extortion",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ],
  "attack_stage": [
    "defense_evasion",
    "impact"
  ],
  "ecosystem": [
    "windows_pe"
  ],
  "is_emerging": false,
  "sources": [
    {
      "name": "Microsoft Defender Threat Encyclopedia - Ransom:Win32/Cmy3u",
      "url": "https://www.microsoft.com/en-us/wdsi/threats/malware-encyclopedia-description?Name=Ransom:Win32/Cmy3u"
    },
    {
      "name": "Kaspersky Threat Intelligence - Trojan-Ransom Overview",
      "url": "https://threats.kaspersky.com/en/threat/Trojan-Ransom.Win32/"
    },
    {
      "name": "MITRE ATT&CK - Data Encrypted for Impact (T1486)",
      "url": "https://attack.mitre.org/techniques/T1486/"
    }
  ],
  "target_platforms": [
    "Windows 11",
    "Windows 10",
    "Windows Server 2022",
    "Windows Server 2019"
  ]
}