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Backdoor:W32/Zxshell.A


First posted on 24 December 2010.
Source: SecurityHome

Aliases :

There are no other names known for Backdoor:W32/Zxshell.A.

Explanation :

Backdoor:W32/Zxshell.A is a DLL file with an exported function ("Install"), which is called to install the backdoor.

Additional DetailsBackdoor:W32/Zxshell.A is similar to other backdoor programs in providing a wide range of functionalities. Some of the functionalities it provides are:

  • CA = Clone an account with "System" privilege
  • CleanEvent = Clean event
  • CloseFW = Close Windows Firewall
  • End = End the backdoor program
  • Execute = Execute program
  • FileTime = Clone timestamp of a file
  • FindPass = Find login password for an account
  • FindDialPass = Find all the dialup account and password
  • Help | ? = Show help file
  • KeyLog = Capture keyboard command
  • LoadDll = Load a DLL into a specified process
  • PortScan = Do the port scan Ps = Show the process
  • RunAs = Just like the Windows "Runas" command
  • SC = Manipulate Windows Service Manager
  • ShareShell = Share the shell
  • ShutDown = Restart/Shutdown the system
  • Sysinfo = Display system information
  • SYNFlood = SYN attack
  • TermSvc = Terminal service
  • TransFile = Upload/Download file to FTP server
  • Uninstall = Uninstall the backdoor
  • User = User account manager
  • ZXARPS = ZXARPS
  • ZXFtpServer = Setup FTP server
  • ZXNC = Just another copy of netcat
  • ZXHttpProxy = Setup HTTP proxy agent
  • ZXHttpServer = Setup HTTP server
  • ZXPlug = install plugins
  • ZXSockProxy = Socks 4 & 5 agent
Upon execution, it will drop a rootkit driver (detected as Rootkit:W32/Zxshell.B)
  • %windir%\system32\_amdevntas.sys

Registry Changes
In order to load the backdoor automatically during the system startup, it needs to install to the system launch point as a system service in the registries:
  • HKLM\System\CurrentControlSet\Services\6to4
    DisplayName = 6to4
    ObjectName = LocalSystem
    Start = 2
    ErrorControl = 1
    Type = 288
    ImagePath = %SystemRoot%\System32\svchost.exe -k netsvcs HKLM\System\CurrentControlSet\Services\6to4\Security
    Security =
  • HKLM\SYSTEM\CurrentControlSet\Services\6to4\Parameters
    ServiceDll = %PATH_TO_BACKDOOR_DLL%
  • HKLM\SYSTEM\CurrentControlSet\Services\6to4\Parameters
    ServiceDllUnloadOnStop = 0
  • HKLM\System\CurrentControlSet\Services\6to4\Control
    ActiveService = 6to4
It will connect to the remote host of the attacker machines. The URL of the remote host is set by the attacker to where the backdoor wants to connect to.

Last update 24 December 2010

 

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