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

Automatic action

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Technical Details

Backdoor: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
  • 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.