Analysis by: Eleazar Valles
ALIASES:

TrojanDownloader:JS/Obfuse.PRWA (MICROSOFT)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

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

It does not have any propagation routine.

It does not have any backdoor routine.

It does not have any information-stealing capability.

  TECHNICAL DETAILS

File Size: 357,402 bytes
File Type: JS
Memory Resident: No
Initial Samples Received Date: 04 Jun 2023

Arrival Details

This Trojan 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 Trojan drops the following files:

  • %Application Data%\[Random characters].txt

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

It adds the following processes:

  • {JRE Directory}\bin\javaw.exe -jar %Application Data%\[Random characters].txt → if JRE is installed
  • %Application Data%\jre7\bin\javaw.exe -jar %Application Data%\[Random characters].txt → if JRE is NOT installed

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

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
ntfsmgr = %Application Data%\jre7\bin\javaw.exe -jar %Application Data%\[Random characters].txt → if JRE is NOT installed

Propagation

This Trojan does not have any propagation routine.

Backdoor Routine

This Trojan does not have any backdoor routine.

Rootkit Capabilities

This Trojan does not have rootkit capabilities.

Information Theft

This Trojan does not have any information-stealing capability.

Other Details

This Trojan does the following:

  • checks if system has Java Runtime Environment (JRE) installed so it could run dropped malicious file (%Application Data%\ntfsmgr.jar) by reading the following registries:
    • HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\JavaSoft\Java Runtime Environment\{JRE Version}\JavaHome
    • HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\{JRE Version}\JavaHome
  • if JRE is not yet installed, it does the following:
    • downloads JRE archive from URL:
      • http://{BLOCKED}t.company/jv/jree.zip
    • saves file as:
      • %Application Data%\jre.zip
    • decompresses it to:
      • %Application Data%\jre7

  SOLUTION

Minimum Scan Engine: 9.800
FIRST VSAPI PATTERN FILE: 18.490.04
FIRST VSAPI PATTERN DATE: 05 Jun 2023
VSAPI OPR PATTERN File: 18.491.00
VSAPI OPR PATTERN Date: 06 Jun 2023

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.XXJSE9EFF047

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

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\Microsoft\Windows\CurrentVersion\Run
    • ntfsmgr = "%Application Data%\jre7\bin\javaw.exe" -jar "%Application Data%\[Random characters].txt"

Step 5

Search and delete this folder

[ Learn More ]
Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden folders in the search result.
  • %Application Data%\jre7

Step 6

Search and delete these files

[ 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.
  • %Application Data%\jre.zip
  • %Application Data%\[Random characters].txt

Step 7

Scan your computer with your Trend Micro product to delete files detected as Trojan.JS.DUNIHI.AMX. 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 the following Trend Micro Support pages for more information:


Did this description help? Tell us how we did.