TROJ_BOKIN.A


 ALIASES:

[leassap.exe]:RDN/Generic Downloader.x!kq (McAfee); BehavesLike.Win32.Malware.wlk (mx-v) (Sunbelt); Found Win32/DH{gRKBEx59IA8iWyU} (AVG)

 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:

  • 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.

  TECHNICAL DETAILS

File Size:

212,757 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

23 Aug 2014

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 creates the following folders:

  • %System Root%\DOCUME~1
  • %System Root%\DOCUME~1\Wilbert
  • %User Profile%\LOCALS~1

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.)

Autostart Technique

This Trojan modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Userinit = "%System%\userinit.exe,%User Temp%\leassap.exe,"

(Note: The default value data of the said registry entry is %Windows%\system32\userinit.exe,.)

Other System Modifications

This Trojan deletes the following files:

  • %User Temp%\tst7.tmp
  • %User Temp%\tst9.tmp
  • %User Temp%\tstB.tmp
  • %User Temp%\tstD.tmp
  • %User Temp%\tstF.tmp

(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 adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets\
Wordpad

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets\
Wordpad\Options

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets\
Wordpad\Text

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets\
Wordpad\RTF

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets\
Wordpad\Word6

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets\
Wordpad\Write

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets\
Wordpad\IP

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets\
Wordpad\Recent File List

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Applets\
Wordpad\Settings

Dropping Routine

This Trojan drops the following files:

  • __tmp_rar_sfx_access_check_57406
  • leassap.exe
  • 20140820.doc

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://www.{BLOCKED}s.willing-net.com
  • {BLOCKED}6.115.72

This report is generated via an automated analysis system.

  SOLUTION

Minimum Scan Engine:

9.700

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

Identify and delete files detected as TROJ_BOKIN.A using either the Startup Disk or Recovery Console

[ Learn More ]

Step 3

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\Microsoft\Windows\CurrentVersion\Applets
    • Wordpad
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Wordpad
    • Options
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Wordpad
    • Text
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Wordpad
    • RTF
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Wordpad
    • Word6
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Wordpad
    • Write
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Wordpad
    • IP
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Wordpad
    • Recent File List
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Wordpad
    • Settings

Step 4

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
    • From: Userinit = "%System%\userinit.exe,%User Temp%\leassap.exe,"
      To: Userinit = ""%Windows%\system32\userinit.exe,""

Step 5

Search and delete these components

[ Learn More ]
There may be some components 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.
  • __tmp_rar_sfx_access_check_57406
  • leassap.exe
  • 20140820.doc

Step 6

Search and delete these folders

[ 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.
  • %System Root%\DOCUME~1
  • %System Root%\DOCUME~1\Wilbert
  • %User Profile%\LOCALS~1

Step 7

Scan your computer with your Trend Micro product to delete files detected as TROJ_BOKIN.A. 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.

Step 8

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %User Temp%\tst7.tmp
  • %User Temp%\tst9.tmp
  • %User Temp%\tstB.tmp
  • %User Temp%\tstD.tmp
  • %User Temp%\tstF.tmp


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