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JS_NEMUCOD.SMOBFUS

October 08, 2016
 Analysis by: Cris Nowell Pantanilla
 ALIASES:

TrojanDownloader:JS/Nemucod.FG (Microsoft), Trojan.JS.Downloader.FUS (F-Secure), JS/TrojanDownloader.Nemucod.BCR (ESET-NOD32)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 REPORTED INFECTION:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Spammed via email


This Trojan arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

It executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

  TECHNICAL DETAILS

File Size:

17,856 bytes

File Type:

JS

Memory Resident:

No

Initial Samples Received Date:

05 Oct 2016

Payload:

Downloads files, Connects to URLs/IPs, Executes files

Arrival Details

This Trojan arrives as an attachment to email messages spammed by other malware/grayware or malicious users.

Installation

This Trojan drops the following non-malicious file:

  • %Desktop%\DECRYPT.txt - Ransom Note
  • %User Temp%\a.txt - Ransom Note

(Note: %Desktop% is the desktop folder, where it usually is C:\Documents and Settings\{user name}\Desktop in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\Desktop in Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

Other System Modifications

This Trojan adds the following registry entries:

HKEY_CLASSES_ROOT\.crypted
(Default) = "Crypted"

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
.crypted
(Default) = "Crypted"

HKEY_CLASSES_ROOT\Crypted\shell\
open\command
(Default) = "notepad.exe "%User Temp%\a.txt""

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
Crypted\shell\open\
command
(Default) = "notepad.exe "%User Temp%\a.txt""

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
Crypted = "%User Temp%\a.txt"

Download Routine

This Trojan accesses the following websites to download files:

  • http://{BLOCKED}iou.com/counter/?ad={data}&id={id}&rnd={number}
  • http://{BLOCKED}kino.ru/counter/?ad={data}&id={id}&rnd={number}
  • http://{BLOCKED}kolkata.org.in/counter/?ad={data}&id={id}&rnd={number}
  • http://{BLOCKED}iajeans.com/counter/?ad={data}&id={id}&rnd={number}
  • http://{BLOCKED}itovik.ru/counter/?ad={data}&id={id}&rnd={number}

It saves the files it downloads using the following names:

  • %User Temp%\a.exe
  • %User Temp%\a.php
  • %User Temp%\a1.exe
  • %User Temp%\a2.exe
  • %User Temp%\php4ts.dll

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It then executes the downloaded files. As a result, malicious routines of the downloaded files are exhibited on the affected system.

  SOLUTION

Minimum Scan Engine:

9.800

FIRST VSAPI PATTERN FILE:

12.818.08

FIRST VSAPI PATTERN DATE:

05 Oct 2016

VSAPI OPR PATTERN File:

12.819.00

VSAPI OPR PATTERN Date:

06 Oct 2016

Step 1

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

Step 2

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_CLASSES_ROOT
    • .crypted
  • In HKEY_CLASSES_ROOT
    • Crypted
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Classes
    • .crypted
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Classes
    • Crypted

Step 3

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
    • Crypted = "%User Temp%\a.txt"

Step 4

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.
%Desktop%\DECRYPT.txt
%User Temp%\a.txt
%User Temp%\a.exe
%User Temp%\a.php
%User Temp%\a1.exe
%User Temp%\a2.exe
%User Temp%\php4ts.dll

Step 5

Scan your computer with your Trend Micro product to delete files detected as JS_NEMUCOD.SMOBFUS. 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.


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