BKDR_THOPER.A

 Analysis by: Michael Cabel

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Dropped by other malware, Downloaded from the Internet


This backdoor arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It does not have any propagation routine.

It opens a random port to allow a remote user to connect to the affected system. Once a successful connection is established, the remote user executes commands on the affected system. It executes commands from a remote malicious user, effectively compromising the affected system.

It does not have any downloading capability.

  TECHNICAL DETAILS

File Size:

155,648 bytes

File Type:

DLL

Memory Resident:

Yes

Initial Samples Received Date:

02 Feb 2012

Payload:

Logs keystrokes, Compromises system security

Arrival Details

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

  • %Application Data%\{Malware File Name}.DLL

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Windows\Profiles\{user name}\Application Data on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Application Data on Windows NT, and C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003.)

It drops the following non-malicious file:

  • %System Root%\Documents and Settings\All Users\Application Data\SSK.LOG

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

Autostart Technique

This backdoor registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{Malware File Name}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\{Malware File Name}\Parameters
ServiceDll = %Application Data%\{Malware File Name}.DLL

Other System Modifications

This backdoor adds the following registry entries as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
LocalService = {Service Name}

It adds the following registry keys as part of its installation routine:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_{Service Name}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Hardware Profiles\0001\System\
CurrentControlSet\Enum\ROOT\
LEGACY_{Service Name}

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Hardware Profiles\Current\System\
CurrentControlSet\Enum\ROOT\
LEGACY_{Service Name}

Propagation

This backdoor does not have any propagation routine.

Backdoor Routine

This backdoor opens a random port to allow a remote user to connect to the affected system. Once a successful connection is established, the remote user executes commands on the affected system.

It executes the following commands from a remote malicious user:

  • Sniff network traffic
  • Gather system information
  • Monitor online activities of the affected user

It connects to the following URL(s) to send and receive commands from a remote malicious user:

  • {BLOCKED}k.ignorelist.com:443
  • pvt.{BLOCKED}c.com:80
  • aicem.{BLOCKED}o.com:80
  • {BLOCKED}c.com:80

Download Routine

This backdoor does not have any downloading capability.

Stolen Information

This backdoor saves the stolen information in the following file:

  • %System Root%\Documents and Settings\All Users\Application Data\SSK.LOG

(Note: %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.)

NOTES:

This Trojan is capable of logging all activities and keystrokes of an infected system.

It does not have rootkit capabilities.

It does not exploit any vulnerability.

  SOLUTION

Minimum Scan Engine:

9.200

FIRST VSAPI PATTERN FILE:

8.750.06

FIRST VSAPI PATTERN DATE:

02 Feb 2012

VSAPI OPR PATTERN File:

8.751.00

VSAPI OPR PATTERN Date:

03 Feb 2012

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Scan your computer with your Trend Micro product and note files detected as BKDR_THOPER.A

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

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 NT\CurrentVersion\SvcHost
    • LocalService = {Service Name}

Step 5

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_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • {Malware File Name}
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root
    • LEGACY_{Service Name}
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware Profiles\0001\System\CurrentControlSet\Enum\ROOT
    • LEGACY_{Service Name}
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Hardware Profiles\Current\System\CurrentControlSet\Enum\ROOT
    • LEGACY_{Service Name}

Step 6

Search and delete this file

[ Learn More ]
There may be some component 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.
  • %System Root%\Documents and Settings\All Users\Application Data\SSK.LOG

Step 7

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


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