TROJ_DROPPER.ZKH

July 10, 2013
 Analysis by: Anthony Joe Melgarejo
 ALIASES:

Infostealer.Viwir (Symantec), Riskware/PasswordRecovery (Fortinet)

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

  TECHNICAL DETAILS

File Size:

3,325,952 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

07 Jul 2013

Arrival Details

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

Installation

This Trojan adds the following folders:

  • %System Root%\users\public\Public Document
  • %All Users Profile%\Msn
  • %All Users Profile%\Msn\Msn2

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %All Users Profile% is the All Users or Common profile folder, which is C:\Documents and Settings\All Users in Windows 2000, XP, and Server 2003, and C:\ProgramData in Windows Vista and 7.)

It drops the following files:

  • %System Root%\users\public\Public Document\aatd.bat
  • %System Root%\users\public\Public Document\bms.klm
  • %System Root%\users\public\Public Document\cond.reg
  • %System Root%\users\public\Public Document\dd.vbs
  • %System Root%\users\public\Public Document\icd.bat
  • %System Root%\users\public\Public Document\ictd.bat
  • %System Root%\users\public\Public Document\ied.bat
  • %System Root%\users\public\Public Document\iewed.bat
  • %System Root%\users\public\Public Document\image.exe
  • %System Root%\users\public\Public Document\keeprun.ini
  • %System Root%\users\public\Public Document\msnd.exe
  • %System Root%\users\public\Public Document\picture viewer.exe
  • %System Root%\users\public\Public Document\PIC_{year}{random string}_ _{random value} .{random number 1}
  • %System Root%\users\public\Public Document\PIC_{year}{random string}_ _{random value} .{random number 2}
  • %System Root%\users\public\Public Document\pid.PDF
  • %System Root%\users\public\Public Document\sad.vbs
  • %All Users Profile%\Msn\Msn2\aatd.bat
  • %All Users Profile%\Msn\Msn2\bms.klm
  • %All Users Profile%\Msn\Msn2\cond.reg
  • %All Users Profile%\Msn\Msn2\dd.vbs
  • %All Users Profile%\Msn\Msn2\icd.bat
  • %All Users Profile%\Msn\Msn2\ictd.bat
  • %All Users Profile%\Msn\Msn2\ied.bat
  • %All Users Profile%\Msn\Msn2\iewed.bat
  • %All Users Profile%\Msn\Msn2\image.exe
  • %All Users Profile%\Msn\Msn2\keeprun.ini
  • %All Users Profile%\Msn\Msn2\msnd.exe
  • %All Users Profile%\Msn\Msn2\picture viewer.exe
  • %All Users Profile%\Msn\Msn2\pid.PDF
  • %All Users Profile%\Msn\Msn2\sad.vbs

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %All Users Profile% is the All Users or Common profile folder, which is C:\Documents and Settings\All Users in Windows 2000, XP, and Server 2003, and C:\ProgramData in Windows Vista and 7.)

Autostart Technique

This Trojan creates the following registry entries to enable automatic execution of dropped component at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
stat = "%All Users Profile%\Msn\Msn2\aatd.bat"

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
stat2 = "%All Users Profile%\Msn\Msn2\aatd.bat"

Other System Modifications

This Trojan modifies the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile
EnableFirewall = "0"

(Note: The default value data of the said registry entry is 1.)

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\SharedAccess\Parameters\
FirewallPolicy\StandardProfile
DoNotAllowExceptions = "0"

(Note: The default value data of the said registry entry is 1.)

Other Details

This Trojan connects to the following possibly malicious URL:

  • ftp.{BLOCKED}stia.com

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

10.144.04

FIRST VSAPI PATTERN DATE:

09 Jul 2013

VSAPI OPR PATTERN File:

10.145.00

VSAPI OPR PATTERN Date:

10 Jul 2013

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

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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • stat = "%All Users Profile%\Msn\Msn2\aatd.bat"
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • stat2 = "%All Users Profile%\Msn\Msn2\aatd.bat"

Step 4

Restore this modified 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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile
    • From: EnableFirewall = "0"
      To: EnableFirewall = 1
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\Parameters\FirewallPolicy\StandardProfile
    • From: DoNotAllowExceptions = "0"
      To: DoNotAllowExceptions = 1

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.
  • %System Root%\users\public\Public Document
  • %All Users Profile%\Msn

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_DROPPER.ZKH. 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.


Did this description help? Tell us how we did.