Analysis by: Alvin Bacani
ALIASES:

Backdoor:Win32/Plimus.2_1 (Microsoft); Backdoor.Win32.Plimus.21 (Kaspersky)

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

  TECHNICAL DETAILS

File Size: 475,965 bytes
Memory Resident: Yes
Initial Samples Received Date: 08 Oct 2013
Payload: Connects to URLs/IPs

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 downloaded from the following remote sites:

  • http://takmabyc.w.{BLOCKED}a.pl/Mario3D.exe

Installation

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

  • %System%\BEKA.exe

(Note: %System% is the Windows system folder, which is usually C:\Windows\System32.)

It drops the following component file(s):

  • %system%\start15.exe

Autostart Technique

This backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
{Blank} = %System%\BEKA.exe

Other System Modifications

This backdoor also creates the following registry entry(ies) as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Except\Data\15
Icon = "{Encrypted Data}"

Backdoor Routine

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

  • Gather System Information
  • List Running Processes
  • Terminate Processes
  • Logout of Windows
  • Perform system reboot
  • Perform system shutdown
  • Capture screen
  • Open / Execute files/URLs
  • Launch command shell
  • Open Telnet
  • Capture Keystrokes
  • Steal email addresses from outlook
  • List Disk and Files
  • Delete Files / Folders
  • Setup FTP Server
  • Upload / Download files

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

  • http://appmsg.{BLOCKED}du.pl/appsvc/appmsg4.asp?

NOTES:

The response from the remote site where this backdoor connects to contains a set of IP addresses with corresponding ports. The IP addresses and ports are used in performing its intended routine.

  SOLUTION

Minimum Scan Engine: 9.700
FIRST VSAPI PATTERN FILE: 10.406.02
FIRST VSAPI PATTERN DATE: 11 Nov 2013
VSAPI OPR PATTERN File: 10.407.00
VSAPI OPR PATTERN Date: 11 Nov 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

Terminate a malware/grayware process

[ Learn More ]

*Note: If the detected process is not displayed in theWindows Task Manager, continue doing the next steps.

     
    • %System%\BEKA.exe

Step 3

Delete this 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_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • {Blank} = %System%\BEKA.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Except\Data\15
    • Icon = "{Encrypted Data}"

Step 4

Search and delete these files

[ 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.
  • %System%\BEKA.exe
  • %System%\start15.exe

Step 5

Scan your computer with your Trend Micro product to delete files detected as BKDR_PLIMUS.M. 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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