1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
|
# Source:
# http://www.iodigitalsec.com/python-cascading-xor-polymorphic-shellcode-generator/
#
# License:
#; Title Python XOR Shellcode Encoder
#; Author npn <npn at iodigitalsec dot com>
#; License http://creativecommons.org/licenses/by-sa/3.0/
#; Legitimate use and research only
#; This program is distributed in the hope that it will be useful,
#; but WITHOUT ANY WARRANTY; without even the implied warranty of
#; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
from __future__ import absolute_import
from __future__ import division
from pwnlib import shellcraft
from pwnlib.asm import asm
from pwnlib.context import context
from pwnlib.encoders.encoder import Encoder
from pwnlib.util.fiddling import xor_pair
from pwnlib.util.lists import group
# Note shellcode assumes it's based at ecx
class i386XorEncoder(Encoder):
r"""Generates an XOR decoder for i386.
>>> context.clear(arch='i386')
>>> shellcode = asm(shellcraft.sh())
>>> avoid = b'/bin/sh\xcc\xcd\x80'
>>> encoded = pwnlib.encoders.i386.xor.encode(shellcode, avoid)
>>> assert not any(c in encoded for c in avoid)
>>> p = run_shellcode(encoded)
>>> p.sendline(b'echo hello; exit')
>>> p.recvline()
b'hello\n'
>>> encoders.i386.xor.encode(asm(shellcraft.execve('/bin/sh')), avoid=bytearray([0x31]))
b'\xd9\xd0\xd9t$\xf4^\xfcj\x07Y\x83\xc6\x19\x89\xf7\xad\x93\xad1\xd8\xabIu\xf7\x00\x00\x00\x00h\x01\x01\x01\x00\x00\x00\x00\x01\x814$\x00\x00\x00\x00.ri\x01\x00\x00\x00\x00h/bi\x00\x00\x00\x01n\x89\xe30\x00\x01\x00\x00\xc90\xd2j\x00\x00\x00\x00\x0bX\xcd\x80'
"""
arch = 'i386'
stub = None
decoder = '''
start:
fnop
fnstenv [esp-0xc]
pop esi
cld
%s
/* add esi, offset */
.byte 0x83, 0xc6, (end-start)
mov edi, esi
loop:
lodsd
xchg eax, ebx
lodsd
xor eax, ebx
stosd
dec ecx
jnz loop
end:
'''
blacklist = set('\x14$1I^tu\x83\x89\x93\xab\xad\xc6\xd8\xd9\xf4\xf7\xfc')
def __call__(self, raw_bytes, avoid, pcreg=''):
while len(raw_bytes) % context.bytes:
raw_bytes += b'\x00'
a, b = xor_pair(raw_bytes, avoid)
mov_ecx = shellcraft.i386.mov('ecx', len(raw_bytes) // context.bytes)
decoder = self.decoder % mov_ecx
decoder = asm(decoder)
for left, right in zip(group(context.bytes, a), group(context.bytes, b)):
decoder += left
decoder += right
return decoder
encode = i386XorEncoder()
|
