Magniber ransomware now infects Windows users via JavaScript files

A recent malicious campaign delivering Magniber ransomware has been targeting Windows home users with fake security updates.

Threat actors created in September websites that promoted fake antivirus and security updates for Windows 10. The downloaded malicious files (ZIP archives) contained JavaScript that initiated an intricate infection with the file-encrypting malware.

A report from HP’s threat intelligence team notes that Magniber ransomware operators demanded payment of up to $2,500 for home users to receive a decryption tool and recover their files. The strain focuses explicitly on Windows 10 and Windows 11 builds.

Windows builds targeted by Magniber
Windows builds targeted by Magniber (HP)

In April 2022, Magniber was seen distributed as a Windows 10 update via a network of malicious websites.

In January, the its operators used Chrome and Edge browser updates to push malicious Windows application package files (.APPX).

Magniber’s new infection chain

In previous campaign, the threat actor used MSI and EXE files. For the recent on, it switched to JavaScript files that had the following names:

  • SYSTEM.Critical.Upgrade.Win10.0.ba45bd8ee89b1.js
  • SYSTEM.Security.Database.Upgrade.Win10.0.jse
  • Antivirus_Upgrade_Cloud.29229c7696d2d84.jse
  • ALERT.System.Software.Upgrade.392fdad9ebab262cc97f832c40e6ad2c.js

These files are obfuscated and use a variation of the “DotNetToJScript” technique to execute a .NET file in the system memory, lowering the risk of detection by antivirus products available on the host.

The .NET file decodes shellcode that uses its own wrapper to make stealthy syscalls, and injects it into a new process before terminating its own.

The shellcode deletes shadow copy files via WMI and disables backup and recovery features through “bcdedit” and “wbadmin.” This increases the chances of getting paid as victims have one less option to recover their files.

To perform this action, Magniber uses a bypass for the User Account Control (UAC) feature in Windows.

It relies on a mechanism that involves creating of a new registry key that allows specifying a shell command. In a later step, the “fodhelper.exe” utility is executed to run a script for deleting the shadow copies.

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