BKDR_SHELL.AS

October 09, 2012
 Analysis by: Abraham Latimer Camba
 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Backdoor

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel:

Dropped by other malware

This backdoor may be dropped by other malware.

It executes commands from a remote malicious user, effectively compromising the affected system.

  TECHNICAL DETAILS

File Size:

28,754 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

22 Aug 2012

Arrival Details

This backdoor may be dropped by the following malware:

Installation

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

  • %User Profile%\Application Data\2019\svchost .exe

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

It creates the following folders:

  • %User Profile%\Application Data\2019

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

Autostart Technique

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
Shell Folders
Startup = "%User Profile%\Application Data\2019"

(Note: The default value data of the said registry entry is %User Startup%.)

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer\
User Shell Folders
Startup = "%User Profile%\Application Data\2019"

(Note: The default value data of the said registry entry is %User Startup%.)

Backdoor Routine

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

  • Perform remote shell commands

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

  • https://baqiwailu.{BLOCKED}o.org

It posts the following information to its command and control (C&C) server:

  • Computer name
  • OEMCP
  • User name

NOTES:

This backdoor copies all files in the following folders:

  • From: %User Startup%
  • To: %User Profile%\Application Data\2019

  SOLUTION

Minimum Scan Engine:

9.200

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

Remove the malware/grayware file that dropped/downloaded BKDR_SHELL.AS

Step 3

Restart in Safe Mode

[ Learn More ]

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders
    • From: Startup = "%User Profile%\Application Data\2019"
      To: Startup = %User Startup%
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders
    • From: Startup = "%User Profile%\Application Data\2019"
      To: Startup = %User Startup%

Step 5

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.
  • %User Profile%\Application Data\2019

Step 6

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