BKDR_SMALL.USCZ

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

It gathers certain information on the affected computer.

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 files:

• %User Temp%\{random}_tmp.cmd

(Note: %User Temp% is the user's temporary folder, where it usually is C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Local\Temp on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It adds the following mutexes to ensure that only one of its copies runs at any one time:

• T2015010901
• T2015012802

Propagation

This backdoor does not have any propagation routine.

Backdoor Routine

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

• Gather Information
• Get Drives Information
• Get File Information
• Find Files
• Create Folder
• Execute Files
• Move File
• Create Files
• Modify Files
• Empty Recycle Bin
• Terminate Process
• Shutdown
• Send Gathered Information
• Perform Remote Shell
• Sleep

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

• http://{BLOCKED}z.{BLOCKED}l.net/{random values}.{random format}
• https://{BLOCKED}z.{BLOCKED}l.net/{random values}.{random format}
  
  where {random format} may be any of the following:
  • asp
  • php
  • jsp
  • aspx
  • htm
  • html
  • shtm
  • shtml
  • cgi
  • xml

As of this writing, the said sites are inaccessible.

Information Theft

This backdoor gathers the following information on the affected computer:

• Volume Information
• Computer Name
• User Name
• OS Version
• Drive Information
• File Information