Cmy3U

Overview

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.

Known aliases

Threat reports may refer to this family under multiple names:

• Ransom:Win32/Cmy3u
• Trojan-Ransom.Win32.Cmy3u
• Win32/Cmy3u
• Cmy3u Ransomware
• Ransom.Cmy3u

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.
• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Tiered Detection Rules (Cisco CAIRN Model)

Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:

rule MALWARE_WIN_CMY3U_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Cmy3U"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "cmy3u" ascii wide nocase
        $s2 = "ransom:win32/cmy3u" ascii wide nocase
        $s3 = "trojan-ransom.win32.cmy3u" ascii wide nocase
        $s4 = "win32/cmy3u" ascii wide nocase
        $s5 = "cmy3u ransomware" ascii wide nocase
        $s6 = "ransom.cmy3u" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Cmy3u (Ransomware) Execution & Triage
id: c3e6bcde-3ee7-51e8-a2a9-197d808f2f52
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Cmy3u malware family. Detects volume shadow copy deletion, boot status
  tampering, and recovery inhibition characteristic of modern ransomware operations.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/cmy3u
- https://malware-families-catalog.systemhelpdesk.com/defensive/ransomware-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.ransomware
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1486
- attack.t1490
- attack.t1083
- attack.t1135
- attack.t1059_003
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \vssadmin.exe
    - \wmic.exe
    - \wbadmin.exe
    - \bcdedit.exe
    CommandLine|contains:
    - delete shadows
    - shadowcopy delete
    - resize shadowstorage
    - recoveryenabled no
    - ignoreallfailures
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: critical

rule MALWARE_WIN_CMY3U_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Cmy3U tradecraft"
        tier = "T3 - Attribution Fingerprint"
        confidence = "High (Confirmed Family Signature)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        // Core family identifier & heuristic payload signatures
        $attrib_str = "cmy3u" ascii wide nocase
        $pe_magic = "MZ" ascii
        $net_marker = "http" ascii nocase
    condition:
        uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. Isolate the endpoint immediately to prevent Cmy3u from downloading and executing its secondary payloads (e.g., ransomware).
2. Audit the Windows Task Scheduler and Registry Run keys to identify and remove the Cmy3u persistence mechanisms.
3. Review firewall and proxy logs to identify the C2 domains Cmy3u attempted to contact, and block them enterprise-wide.
4. Capture a live memory image (RAM dump) to extract the injected Cmy3u modules and identify the secondary payloads.

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not close an incident simply because the initial Cmy3u dropper was quarantined; always verify if secondary payloads were downloaded.
2. Avoid relying solely on manual file deletion, as the injected processes will likely just recreate the dropped binaries.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - Ransom:Win32/Cmy3u
• Kaspersky Threat Intelligence - Trojan-Ransom Overview
• MITRE ATT&CK - Data Encrypted for Impact (T1486)
• Search "cmy3u" on VirusTotal (External Analysis)
• Search "cmy3u" on Any.Run (Sandbox Sandbox)
• Search "cmy3u" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Ransomware)

Explore other documented threats in the same operational category:

• Killmbr
• Cinmus
• Genericrxgm
• Elevate
• Isnev
• Wiliky
• Phny
• Vehidis

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/cmy3u.json

Ecosystem & Interactive Environments

This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.