Analysis by: James Vargas
ALIASES:

Trojan.JS.Agent (IKARUS); JS/Agent.AX trojan (NOD32)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

  TECHNICAL DETAILS

File Size: 11,197 bytes
File Type: JS
Initial Samples Received Date: 26 Mar 2020
Payload: Drops files, Connects to URLs/IPs

Arrival Details

This Backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Backdoor drops and executes the following files:

  • %User Profile%\ntuser64.dat:WinNTSrv.js

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name} on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

It adds the following processes:

  • schtasks.exe /Create /F /TN \"VPNdriver\" /TR \"wscript C:\Users\{username}\ntuser64.dat:WinNTSrv.js\" /SC Minute /MO 5

Other System Modifications

This Backdoor adds the following registry entries as part of its installation routine:

HKEY_CURRENT_USER\Software\ApplicationContainer\
Appsw64
ShimV4 = {URLs}

HKEY_CURRENT_USER\Software\ApplicationContainer\
Appsw64
SetupServiceKey = {10 Random Characters}

Backdoor Routine

This Backdoor executes the following commands from a remote malicious user:

  • Executes a JavaScript program

It connects to the following websites to send and receive information:

  • http://{BLOCKED}co.info/rss/{base64encoded-string}
  • http://{BLOCKED}a7.info/rss/{base64encoded-string}
  • http://{BLOCKED}3x.info/rss/{base64encoded-string}

Other Details

This Backdoor adds the following registry keys:

HKEY_CURRENT_USER\Software\ApplicationContainer

HKEY_CURRENT_USER\Software\ApplicationContainer\
Appsw64

It does the following:

  • where:
    • {base64encoded-string} - random order of {version, gid, username, pcname, domain, corp, id}

It adds the following scheduled tasks:

  • Task Name = VPNdrivers
    • Trigger = One Time; Repeat every 5 minutes indefinitely
    • Action = wscript %User Profile%\\ntuser64.dat:WinNTSrv.js

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000(32-bit), XP, and Server 2003(32-bit), or C:\Users\{user name} on Windows Vista, 7, 8, 8.1, 2008(64-bit), 2012(64-bit) and 10(64-bit).)

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 15.774.02
FIRST VSAPI PATTERN DATE: 30 Mar 2020
VSAPI OPR PATTERN File: 15.775.00
VSAPI OPR PATTERN Date: 31 Mar 2020

Step 1

Trend Micro Predictive Machine Learning detects and blocks malware at the first sign of its existence, before it executes on your system. When enabled, your Trend Micro product detects this malware under the following machine learning name:

     
    • Downloader.JS.TRX.XXJSE9EFF012

Step 2

Before doing any scans, Windows 7, Windows 8, Windows 8.1, and Windows 10 users must disable System Restore to allow full scanning of their computers.

Step 3

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 4

Restart in Safe Mode

[ Learn More ]

Step 5

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\ApplicationContainer\Appsw64\
    • ShimV4 = {URLs}
  • In HKEY_CURRENT_USER\Software\ApplicationContainer\Appsw64\
    • SetupServiceKey = {random 10 characters}

Step 6

Delete this registry key

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_CURRENT_USER\Software\ApplicationContainer\Appsw64

Step 7

Search and delete this file

[ Learn More ]
There may be some files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the "More advanced options" option to include all hidden files and folders in the search result.
  • %User Profile%\ntuser64.dat:WinNTSrv.js

Step 8

Restart in normal mode and scan your computer with your Trend Micro product for files detected as Backdoor.JS.VALAK.THBFBO. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


Did this description help? Tell us how we did.