Home > Threat descriptions >

Backdoor:W32/PcClient.VK

Classification

Category: Malware

Type: Backdoor

Aliases: Backdoor.Pcclient, Backdoor.Win32.PcClient, Backdoor:Win32/PcClient (Microsoft) , BKDR_PCCLIENT.VK (Trend Micro), Backdoor.Formador (Symantec)

Summary


A remote administration utility which bypasses normal security mechanisms to secretly control a program, computer or network.

Removal


Automatic action

Based on the settings of your F-Secure security product, it will either automatically delete, quarantine or rename the detected program or file, or ask you for a desired action.

Knowledge Base

Find the latest advice in our Community Knowledge Base.

About the product

See the manual for your F-Secure product on the Help Center.

Contact Support

Chat with or call an expert for help.

Submit a sample

Submit a file or URL for further analysis.

Technical Details


Backdoor:W32/PcClient.VK is seen in the wild as the payload file installed on a host machine by a specially crafted Microsoft PowerPoint file that contains exploit code.

When run, PcClient.VK attempts to hide processes, files, registry data and network connections, allows the attacker to perform arbitrary actions on machine, and steals sensitive information from an infected computer.

Installation

Once execution of PcClient.VK been initiated, its executable component will drop the following hard-coded files in the Windows System directory:

  • Ybrcuugm.d1l - Backdoor
  • Ybrcuugm.dll - Keylogger

Note: the file size of Ybrcuugm.d1l might vary due to garbage code appended at the end of the file.

It will also drop the following driver that will communicate with the dll files in order to hide the malware's processes, registry entries and files:

  • %sysdir%\drivers\Ybrcuugm.sys

Moreover it also hides some network traffic that the PcClient.VK uses.

Payload

Part of the malware's payload is that is logs all the keystrokes made by the user and saves it to the following file:

  • %sysdir%\log.txt

It then sends this file to a remote hacker.

Backdoor

The malware's backdoor routine is injected into svchost.exe, which is capable doing the following:

  • updating itself
  • remote execution

This malware connects to the following site:

  • http://baas.8866.org/[BLOCKED]ex.asp
Registry

It modifies the following known registry entry as its autostart technique:

Data before:

  • [HKLM\SYSTEM\CurrentControlSet\Services\dmserver\Parameters] ServiceDll = %sysdir%\dmserver.dll

Data after:

  • [HKLM\SYSTEM\CurrentControlSet\Services\dmserver\Parameters] ServiceDll = %sysdir%\Ybrcuugm.d1l

In order for the system to work normally, Ybrcuugm.dll will execute its malicious routine and then pass the correct parameter to the original dmserver.dll.

It also adds the following autostart registry entry for the driver:

  • [HKLM\System\ControlSet001\Services\Ybrcuugm] ImagePath= C:\WINDOWS\system32\drivers\Ybrcuugm.sys