BKDR_THOPER.AB

 Analysis by: Mark Joseph Manahan

 ALIASES:

TrojanDownloader:Win32/Thoper.D (Microsoft), BackDoor-FANI!90C57F5CACD3 (McAfee)

 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: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Downloaded from the Internet, Dropped by other malware

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 executes then deletes itself afterward.

It does not have any propagation routine.

It executes commands from a remote malicious user, effectively compromising the affected system. It connects to a website to send and receive information.

It does not have any downloading capability.

  TECHNICAL DETAILS

File Size:

160,400 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

25 Apr 2013

Payload:

Steals information,Connects to URLs/IPs, Compromises network 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 and executes the following files:

  • %All Users Profile%\Application Data\mspool.DLL - also detected as BKDR_THOPER.AB

(Note: %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 non-malicious file:

  • %User Temp%\3.doc

(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 then deletes itself afterward.

Autostart Technique

This backdoor registers its dropped component as a system service to ensure its automatic execution at every system startup. It does this by creating the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\mspool

Propagation

This backdoor does not have any propagation routine.

Backdoor Routine

This backdoor executes the following commands from a remote malicious user:

  • File Manipulation
  • Registry Management
  • Service Management
  • Process Management
  • Get System Information (Disk Information, OS Version, Computer Name, Drive Information, Volume Information, Network Information)
  • Retrieve cache passwords
  • Perform shell command
  • Donwload and execute arbitrary file
  • Microsoft Database Query
  • Remote desktop connection
  • Shutdown, Restart and Lock Workstation
  • Display a message box
  • Manage Application Windows
  • Log keystrokes
  • Capture screenshots

It connects to the following websites to send and receive information:

  • {BLOCKED}m.{BLOCKED}-show.org:443

Download Routine

This backdoor does not have any downloading capability.

Other Details

This backdoor connects to the following URL(s) to check for an Internet connection:

  • download.windowsupdate.com

NOTES:

It does not have rootkit capabilities.

It does not exploit any vulnerability.

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.876.06

FIRST VSAPI PATTERN DATE:

25 Apr 2013

VSAPI OPR PATTERN File:

9.877.00

VSAPI OPR PATTERN Date:

25 Apr 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 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\mspool

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%\3.doc

Step 5

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