metasploit-framework/modules/encoders/x86/add_sub.rb

150 lines
3.5 KiB
Ruby

##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##
require 'msf/core'
class Metasploit3 < Msf::Encoder
Rank = ManualRanking
def initialize
super(
'Name' => 'Add/Sub Encoder',
'Description' => %q{
Encodes payload with add or sub instructions. This idea came
from (offensive-security) muts' hp nnm 7.5.1 exploit.
},
'Author' => 'Melih Sarica <ms[at]sevure.com>',
'Arch' => ARCH_X86,
'License' => MSF_LICENSE,
'Decoder' =>
{
'BlockSize' => 4
})
end
def add_or_sub(avchars)
add = [0x05, 0x50, 0x58, 0x25, 0x54, 0x5C]
sub = [0x2D, 0x50, 0x58, 0x25, 0x54, 0x5C]
return 1 if add.all?{|ch|avchars.include?ch.chr}
return 2 if sub.all?{|ch|avchars.include?ch.chr}
return 0
end
def write_inst(inst, mcode)
@data << inst
if mcode != 0
for i in 0...4
t = mcode & 0x000000FF;
@data << t
mcode = mcode >> 8;
end
end
end
def rand_with_av_chars()
t2 = 0
for i in 0...4
c = @avchars[rand(@avchars.size)].ord.to_i()
t2 = t2 <<8
t2 += c
end
return t2
end
def check_non_av_chars(target)
for i in 0...4
t = target & 0x000000FF;
return true if not @avchars.include?t.chr
target = target >> 8;
end
return false
end
def encode_inst(target)
begin
a = rand_with_av_chars()
b = rand_with_av_chars()
c = target - a - b if @set == 1
c = 0 - target - a - b if @set == 2
c = c%(0xFFFFFFFF+1)
end while check_non_av_chars(c) == true
write_inst(@inst["opcode"], a)
write_inst(@inst["opcode"], b)
write_inst(@inst["opcode"], c)
end
def encode_shellcode(target, z1, z2)
write_inst(@inst["and"], z1);
write_inst(@inst["and"], z2);
encode_inst(target);
write_inst(@inst["push"], 0);
end
def decoder_stub(state)
buf = ""
shellcode = state.buf.split(//)
while shellcode.size>0
buf << shellcode.pop(4).join
end
state.buf = buf
@data = ""
@avchars = ""
for i in 0..255
@avchars = @avchars + i.chr.to_s if not state.badchars.include?i.chr.to_s
end
offset = (datastore['BufferOffset'] || 0).to_i
@inst = {}
@set = add_or_sub(@avchars)
if @set == 0 then
raise EncodingError, "Bad character list includes essential characters."
exit
elsif @set == 1 then #add
@inst["opcode"] = 0x05
else #sub
@inst["opcode"] = 0x2d
end
@inst["push"] = 0x50
@inst["pop"] = 0x58
@inst["and"] = 0x25
@inst["push_esp"] = 0x54
@inst["pop_esp"] = 0x5c
if state.buf.size%4 != 0 then
raise EncodingError, "Shellcode size must be divisible by 4, try nop padding."
exit
end
#init
write_inst(@inst["push_esp"], 0)
write_inst(@inst["pop"], 0)
encode_inst(offset)
write_inst(@inst["push"], 0)
write_inst(@inst["pop_esp"], 0)
#zeroing registers
begin
@z1 = rand_with_av_chars()
@z2 = rand_with_av_chars()
end while @z1&@z2 != 0
decoder = @data
return decoder
end
def encode_block(state, block)
#encoding shellcode
@data = ""
target = block.split(//)
return if target.size<4
t = 0
for i in 0..3
t1 = target[3-i][0].ord.to_i
t = t<<8
t = t + t1
end
encode_shellcode(t, @z1, @z2);
encoded = @data
return encoded
end
end