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TROJ_VKHOST.SMA

March 25, 2013
 Analysis by: Sabrina Lei Sioting
 ALIASES:

Trojan:Win32/Meredrop (Microsoft), Packed.Generic.366 (Symantec), PWS-Zbot.gen.hv (McAfee), Mal/Katusha-J (Sophos), Trojan.Win32.Zbot.hv (Sunbelt), W32/ZeroAccess.B!tr (Fortinet), Trojan-Downloader.Win32.Cbeplay (Ikarus),

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • 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 executes the files it drops, prompting the affected system to exhibit the malicious routines they contain.

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size:

54,272 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

20 Sep 2012

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 non-malicious files:

  • %User Temp%\b.ico
  • %User Temp%\dumb13145
  • %User Temp%\{random} - saves strings to be written to system's HOSTS file

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

Its DLL component is injected to the following process(es):

  • iexplore.exe
  • chrome.exe
  • opera.exe
  • firefox.exe

Autostart Technique

This Trojan drops the following shortcut pointing to its copy in the User Startup folder to enable its automatic execution at every system startup:

  • {random}.lnk

Dropping Routine

This Trojan drops the following files:

  • %User Temp%\{random}.vbs - detected as VBS_VKHOST.SMB

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

It executes the files it drops, prompting the affected system to exhibit the malicious routines they contain.

Download Routine

This Trojan connects to the following website(s) to download and execute a malicious file:

  • http://{BLOCKED}rikpres.info/js/data/ex.dll

It saves the files it downloads using the following names:

  • %User Temp%\{random1}
  • %User Temp%\{random}.dll

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

As of this writing, the said sites are inaccessible.

NOTES:

This Trojan modifies the affected system's HOSTS files to prevent a user from accessing certain websites. It does this by copying the following strings from %User Temp%\{random}:

  • {BLOCKED}22.41 odnoklassniki.ru
  • {BLOCKED}22.41 www.facebook.com
  • {BLOCKED}22.41 www.twitter.com
  • {BLOCKED}22.41 vkontakte.ru
  • {BLOCKED}22.41 ru-ru.facebook.com
  • {BLOCKED}22.41 www.odnoklassniki.ru
  • {BLOCKED}22.41 vk.com
  • {BLOCKED}22.41 www.vkontakte.ru
  • {BLOCKED}22.41 www.vk.com
  • {BLOCKED}22.41 facebook.com
  • {BLOCKED}22.41 twitter.com

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.410.03

FIRST VSAPI PATTERN DATE:

20 Sep 2012

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

Restart in Safe Mode

[ Learn More ]

Step 3

Remove the malware/grayware file dropped/downloaded by TROJ_VKHOST.SMA

    VBS_VKHOST.SMB

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.
  • %User Temp%\b.ico
  • %User Temp%\dumb13145
  • %User Temp%\{random}
  • %User Temp%\{random1}
  • %User Temp%\{random}.dll
  • %User Startup%\{random}.lnk

Step 5

Remove these strings added by the malware/grayware/spyware in the HOSTS file

[ Learn More ]
     
    • {BLOCKED}22.41 odnoklassniki.ru
    • {BLOCKED}22.41 www.facebook.com
    • {BLOCKED}22.41 www.twitter.com
    • {BLOCKED}22.41 vkontakte.ru
    • {BLOCKED}22.41 ru-ru.facebook.com
    • {BLOCKED}22.41 www.odnoklassniki.ru
    • {BLOCKED}22.41 vk.com
    • {BLOCKED}22.41 www.vkontakte.ru
    • {BLOCKED}22.41 www.vk.com
    • {BLOCKED}22.41 facebook.com
    • {BLOCKED}22.41 twitter.com
"

Step 6

Scan your computer with your Trend Micro product to delete files detected as TROJ_VKHOST.SMA. 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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