Jenxcus

Overview

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).

Understanding Jenxcus (VBScript Worms)
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.

Execution and Spreading Mechanics
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`).

Indicators of Compromise & Impact
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.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Tactical Mitigations

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

• T1059.005: Restrict execution of scripting languages such as PowerShell, VBScript, or Python to authorized administrators. Enforce Script Block Logging.

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_JENXCUS {
    meta:
        description = "Detects Jenxcus (trojan)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "jenxcus" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Jenxcus Activity
id: 481fa697fab862eea4a02d67f59a292e
status: experimental
description: Detects generic indicators of the jenxcus malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*jenxcus*"
    condition: selection
level: medium

Containment & Response Steps

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

1. 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.
2. 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.
3. Identify the Dynamic DNS domains the script is contacting in the VBS code and block them at the corporate proxy/firewall.
4. Audit the Registry Run keys and Startup folders across the network to identify and remove the persistence mechanisms.

What to Avoid

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

1. Do not allow the use of unencrypted, unmanaged USB drives, as they are the primary vector for Jenxcus.
2. Avoid relying solely on file-based antivirus; heavily obfuscated VBScript requires behavioral monitoring (EDR) of the `wscript.exe` process.

References & External Analysis

• Search "jenxcus" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: trojan)

Explore other malware families in the same category:

• Vilsel
• Webdevaz
• Banpak
• 6B47672C
• Amavaldo

Machine-readable

Get this profile as JSON: https://jordanricky1604-ship-it.github.io/malware-families-catalog/api/jenxcus.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.