BKDR_POSTBOT.G

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.

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

• swdk1wgs5dre

Other System Modifications

This backdoor adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer
MMID = "{random value}"

Propagation

This backdoor does not have any propagation routine.

Backdoor Routine

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

• Enumerate all drives with corresponding drive types
• Enumerate files and directories
• Copy, move, rename, or delete files
• Create directories
• Create or terminate processes
• Copy %System%\cmd.exe as %User Temp%\ms38340fhgs.exe
• Perform remote shell
• Upload files to C&C server
• Download files from C&C server
• Execute the file %System%\svch0st.exe with the parameter /u
• Execute the file %System%\svch0st.exe with the parameter /g
• Sleep for a specified amount of time

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

• {C&C domain name}/{8 random characters}{hard-coded string}
  where {hard-coded string} can be any of the following:
  • 815.php
  • 91b.php
  • 082.php
  • 45f.php
  • 682.php
  • 739.php
  • d93.php
  • eb4.php
  • f27.php
  • 1bc.php
  • 2da.php
  • 3e6.php
  • 472.php
  • 5c2.php
  • 617.php
  • 7f8.php
  • a26.php
  • 292.php
  • 3a2.php
  • c19.php
  • 18c.php
  • 51d.php

Download Routine

This backdoor saves the files it downloads using the following names:

• %System%\svch0st.exe

(Note: %System% is the Windows system folder, where it usually is C:\Windows\System32 on all Windows operating system versions.)

NOTES:

It may use proxy connections by connecting to the following URL:

• {Proxy server name}:{Port Number}

The proxy server name and port number depends on the registry key "mmsoft". If not present, it uses the default proxy settings.

It accesses the following URL to read its configuration:

• http://{BLOCKED}cj.com/blog/wp-includes/pomo/index.php

Its configuration contains the C&C domain name information. However, as of this writing, the said URL is already inaccessible.

It does not have rootkit capabilities.

It does not exploit any vulnerability.