Analysis by: Francis Xavier Antazo
 PLATFORM:

Windows

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

  • 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 may be dropped by other malware.

It executes then deletes itself afterward.

It executes commands from a remote malicious user, effectively compromising the affected system. However, as of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 500,192 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 25 Jun 2015
Payload: Collects system information

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.

It may be dropped by the following malware:

  • CHM_ZXSHELL.B

Installation

This backdoor drops the following component file(s):

  • %System%\WinUser.dat (detected as BKDR_ZXSHELL.B)

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

It drops and executes the following files:

  • %System%\mscorsv.dll (detected as BKDR_ZXSHELL.B)

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

It adds the following processes:

  • rundll32.exe

It executes then deletes itself afterward.

Autostart Technique

This backdoor creates the following service using its DLL component:

  • 6to4

Backdoor Routine

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

  • end current task
  • run arbitrary files
  • show help
  • share shell to other
  • send system info
  • Download or upload files via ftp
  • Uninstall

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

  • {BLOCKED}pan.{BLOCKED}s.info

However, as of this writing, the said sites are inaccessible.

Information Theft

This backdoor gathers the following data:

  • OS version
  • disk space
  • RAM
  • host name
  • organization
  • registered organization
  • owner
  • registered owner
  • drive list and description

  SOLUTION

Minimum Scan Engine: 9.750
FIRST VSAPI PATTERN FILE: 11.752.05
FIRST VSAPI PATTERN DATE: 25 Jun 2015
VSAPI OPR PATTERN File: 11.753.00
VSAPI OPR PATTERN Date: 26 Jun 2015

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

Note that not all files, folders, and registry keys and entries are installed on your computer during this malware's/spyware's/grayware's execution. This may be due to incomplete installation or other operating system conditions. If you do not find the same files/folders/registry information, please proceed to the next step.

Step 3

Restart in Safe Mode

[ Learn More ]

Step 4

Restart in Safe Mode, and then 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
    • 6to4

Step 5

Remove the malware/grayware file that dropped/downloaded BKDR_ZXSHELL.B. (Note: Please skip this step if the threat(s) listed below have already been removed.)

    • CHM_ZXSHELL.B

Step 6

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