{
  "family": "nemucod",
  "sample_count": 1,
  "category": "ransomware",
  "description": "TrojanDownloader:JS/Nemucod (or VBS/Nemucod) is one of the most prolific and historically significant malware downloaders. Primarily distributed via massive spam campaigns, Nemucod arrives as a tiny, heavily obfuscated JavaScript (`.js`) or VBScript (`.vbs`) file hidden inside a ZIP archive. Its sole purpose is to execute via the Windows Script Host (`wscript.exe`), silently connect to a compromised website, and download a catastrophic secondary payload—most famously, ransomware families like Locky, Cerber, or TeslaCrypt (`T1105`).<br><br><b>Understanding Nemucod (Script Downloaders)</b><br>To an end-user, they receive a fake invoice or shipping notification, extract the ZIP, double-click the seemingly harmless file, and see nothing happen. Minutes later, their files are encrypted. For a security team, Nemucod represents the danger of allowing script execution from user directories. It is an 'Initial Access Broker' that paves the way for total data loss.<br><br><b>Execution and Dropper Mechanics</b><br>The infection chain relies on social engineering (`T1566.001`) to trick the user into extracting and running the script. Because Windows associates `.js` and `.vbs` files with `wscript.exe` by default, double-clicking them executes the code (`T1059.007`). The script itself is heavily obfuscated (using string concatenation, random variables, and encoding) to evade static email filters (`T1027`). Once running, it uses COM objects (like `MSXML2.XMLHTTP`) to download the secondary payload (usually an `.exe` or a `.dll`) to the `%Temp%` folder, and then executes it.<br><br><b>Indicators of Compromise & Impact</b><br>The impact is almost always a severe secondary infection (Ransomware or Banking Trojans). Host-based IoCs include EDR alerts for `wscript.exe` or `cscript.exe` executing from within zip archives or `%Temp%` directories, and `wscript.exe` spawning unexpected child processes (like `cmd.exe` or dropping unknown executables). Network IoCs involve the `wscript.exe` process making outbound HTTP GET requests to compromised WordPress sites or unknown domains to fetch the payload.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [
    {
      "@type": "Question",
      "name": "What is Nemucod and what threat category does it belong to?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Nemucod is classified as a Ransomware. Documented across security telemetry, it is engineered to execute unauthorized operations, establish persistent footholds on target endpoints, and facilitate malicious campaigns targeting enterprise and individual environments."
      }
    },
    {
      "@type": "Question",
      "name": "How does Nemucod establish persistence and evade defensive controls?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Nemucod typically establishes persistence through registry run keys, scheduled tasks, or service installations, while evading signature-based antivirus solutions through code obfuscation, memory injection, or anti-analysis sandbox checks."
      }
    },
    {
      "@type": "Question",
      "name": "What are the essential incident response steps for mitigating a Nemucod compromise?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Security teams responding to Nemucod should immediately isolate affected endpoints from the network, perform memory triage to capture volatile forensic artifacts, audit registry and startup persistence mechanisms, revoke exposed user credentials, and restore systems from verified, clean backups."
      }
    },
    {
      "@type": "Question",
      "name": "What cryptographic algorithms and file targeting techniques does Nemucod employ during execution?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Nemucod typically leverages hybrid cryptographic architectures combining symmetric stream or block ciphers (such as AES-256 or ChaCha20) for rapid file encryption with asymmetric algorithms (such as RSA-2048 or Curve25519) to securely protect the session keys. It aggressively targets sensitive file extensions including corporate documents, databases, virtual disks, and backups while systematically executing commands to delete Volume Shadow Copies (vssadmin delete shadows /all /quiet) and disable system recovery options."
      }
    },
    {
      "@type": "Question",
      "name": "Are decryptors available for Nemucod, and what is the recommended recovery procedure?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Decryption availability for Nemucod depends on whether security researchers or law enforcement (such as the No More Ransom initiative) have recovered the master private keys or discovered flaws in its key generation routines. Victims should never pay the extortion demand, as payment fuels criminal operations without guaranteeing file restoration. The recommended recovery procedure entails isolating infected hosts, conducting forensic disk imaging, identifying the root access vector, and restoring validated systems from immutable offline backups."
      }
    }
  ],
  "faq_count": 5,
  "mitre_attack": [
    "T1105",
    "T1566.001",
    "T1059.007",
    "T1027"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1059.007",
      "name": "Command and Scripting Interpreter: JavaScript/JScript (Executing the obfuscated downloader payload via WScript)",
      "tactic": "Execution"
    },
    {
      "id": "T1105",
      "name": "Ingress Tool Transfer (Downloading the secondary payload, such as Locky ransomware)",
      "tactic": "Command and Control"
    },
    {
      "id": "T1566.001",
      "name": "Phishing: Spearphishing Attachment (Primary distribution method via ZIP files)",
      "tactic": "Initial Access"
    },
    {
      "id": "T1027",
      "name": "Obfuscated Files or Information (Heavy obfuscation of the script to bypass email gateways)",
      "tactic": "Defense Evasion"
    }
  ],
  "containment_steps": [
    "Isolate the endpoint *immediately*; if Nemucod has executed, a ransomware payload is likely actively encrypting files.",
    "Use EDR to trace the execution chain: locate the original spam email, the extracted script, and the domains it contacted.",
    "Block the identified payload delivery domains at the corporate firewall to prevent other users who received the spam from downloading the ransomware.",
    "Change the default Windows file association for `.js` and `.vbs` files to open with Notepad instead of `wscript.exe` via Group Policy (GPO)."
  ],
  "what_to_avoid": [
    "Do not allow `wscript.exe` to execute scripts originating from `%Temp%` or `%Downloads%` directories without strict application control.",
    "Avoid relying solely on email attachment scanning, as the obfuscated scripts are often designed to bypass static signature checks."
  ],
  "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,
  "target_platforms": [
    "Windows 11",
    "Windows 10",
    "Windows Server 2022",
    "Windows Server 2019"
  ]
}