{
  "family": "jenxcus",
  "sample_count": 4,
  "category": "trojan",
  "description": "Worm:VBS/Jenxcus (often referred to as Houdini or Dinihu) is a prolific, script-based worm and Remote Access Trojan (RAT) written entirely in Visual Basic Script (VBScript). It is notorious for its ability to rapidly propagate across networks via removable media (USB drives) and for providing attackers with a highly persistent, fileless-style backdoor that relies almost entirely on built-in Windows administrative tools (Living off the Land).<br><br><b>Understanding Jenxcus (VBScript Worms)</b><br>To an end-user, a Jenxcus infection often starts when they plug in a USB drive and click what appears to be a folder, but is actually a malicious shortcut (`.lnk` file). For a SOC analyst, Jenxcus is a frustrating threat because it is highly evasive; the entire malware payload is often just a few lines of obfuscated text running inside the legitimate `wscript.exe` process, making it difficult for traditional, file-based AV to detect.<br><br><b>Execution and Spreading Mechanics</b><br>Jenxcus typically arrives via spear-phishing or infected USB drives (`T1091`). When executed (`T1059.005`), the VBScript heavily obfuscates its core logic to evade static analysis (`T1027`). It establishes persistence by dropping a copy of the VBS script into the `%AppData%` or `Startup` folder and creating a Registry Run key pointing to it (`T1547.001`). For propagation, it constantly monitors the system for new removable drives. When a USB is inserted, it copies its VBScript to the drive, hides all legitimate folders on the drive (`T1564.001`), and creates malicious Windows Shortcut (`.lnk`) files (`T1102.001`) with the same names and icons as the hidden folders. When the next victim clicks the 'folder', the shortcut executes the VBScript and then opens the hidden folder, maintaining the deception. Once active, the script beacons out to a C2 server (often using dynamic DNS services) allowing the attacker to download and execute arbitrary files, run shell commands, or update the worm itself (`T1105`).<br><br><b>Indicators of Compromise & Impact</b><br>The impact is a persistent backdoor and the rapid spread of infection across air-gapped or segmented networks via USBs. Host-based IoCs include EDR alerts for `wscript.exe` or `cscript.exe` executing scripts from the `%AppData%` or `%Temp%` directories, or `wscript.exe` making outbound network connections. The presence of hidden folders and corresponding `.lnk` files on USB drives is a definitive indicator.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1091",
    "T1547.001",
    "T1059.005",
    "T1564.001"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1059.005",
      "name": "Command and Scripting Interpreter: Visual Basic",
      "tactic": "Execution"
    },
    {
      "id": "T1091",
      "name": "Replication Through Removable Media (USB Spreading)",
      "tactic": "Lateral Movement"
    },
    {
      "id": "T1564.001",
      "name": "Hide Artifacts: Hidden Files and Directories (Hiding USB folders)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1547.001",
      "name": "Boot or Logon Autostart Execution",
      "tactic": "Persistence"
    }
  ],
  "containment_steps": [
    "Enforce strict Group Policies to disable Windows AutoRun/AutoPlay and restrict the execution of `.vbs` and `.vbe` files (via Windows Script Host) by standard users.",
    "Use the command line (`attrib -h -s /s /d driveletter:\\*.*`) to unhide the legitimate files on infected USB drives, and then delete the malicious `.lnk` and `.vbs` files.",
    "Identify the Dynamic DNS domains the script is contacting in the VBS code and block them at the corporate proxy/firewall.",
    "Audit the Registry Run keys and Startup folders across the network to identify and remove the persistence mechanisms."
  ],
  "what_to_avoid": [
    "Do not allow the use of unencrypted, unmanaged USB drives, as they are the primary vector for Jenxcus.",
    "Avoid relying solely on file-based antivirus; heavily obfuscated VBScript requires behavioral monitoring (EDR) of the `wscript.exe` process."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}