TROJ_DLOADER.EXTA

 Analysis by: Adrian Cofreros

 ALIASES:

Win32/TrojanDownloader.Small.POU(NOD32),Trojan.Win32.Scar.ibom(Kaspersky),Trojan-PWS.Win32.Executant.d(IKARUS)

 PLATFORM:

Windows

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW


This Trojan may be dropped by other malware.

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

65,536 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

11 Nov 2014

Payload:

Connects to URLs/IPs

Arrival Details

This Trojan may be dropped by the following malware:

  • TROJ_MDROP.EXTA

Installation

This Trojan drops the following copies of itself into the affected system:

  • {All Users' My Music folder}\AcroRd32Info.exe

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
ShStatEXE = "{All Users' My Music folder}\AcroRd32Info.exe"

Download Routine

This Trojan accesses the following websites to download files:

  • http://www.{BLOCKED}estate.com/img/member.php?id={value based on the host name of affected system}{value of language identifier of the affected system}

It saves the files it downloads using the following names:

  • %User Temp%\tmp{random}.dat

(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.)

As of this writing, the said sites are inaccessible.

NOTES:

It drops the following file as part of processing contents(decryption etc.) of 'tmp{random}.dat'.

  • %User Temp%\tmp{random}.b6

It drops the following final output file:

  • %User Temp%\tmp{random}.exe -it can execute this file if file type is executable.

  SOLUTION

Minimum Scan Engine:

9.700

FIRST VSAPI PATTERN FILE:

11.254.01

FIRST VSAPI PATTERN DATE:

03 Nov 2014

VSAPI OPR PATTERN File:

11.255.00

VSAPI OPR PATTERN Date:

04 Nov 2014

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

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 3

Remove malware/grayware files that dropped/downloaded TROJ_DLOADER.EXTA. (Note: Please skip this step if the threats listed below have already been removed.)

     
    • TROJ_MDROP.EXTA

Step 4

Identify and terminate files detected as TROJ_DLOADER.EXTA

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

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\Microsoft\Windows\CurrentVersion\Run
    • ShStatEXE = "{All Users' My Music folder}\AcroRd32Info.exe"

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.  
  • %User Temp%\tmp{random}.dat
  • %User Temp%\tmp{random}.b6
  • %User Temp%\tmp{random}.exe

Step 7

Scan your computer with your Trend Micro product to delete files detected as TROJ_DLOADER.EXTA. 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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