Class: Rex::Encoder::Alpha2::AlphaMixed

Inherits:
Generic
  • Object
show all
Defined in:
lib/rex/encoder/alpha2/alpha_mixed.rb

Class Method Summary collapse

Methods inherited from Generic

add_terminator, default_accepted_chars, encode, encode_byte, gen_second

Class Method Details

.gen_decoder(reg, offset) ⇒ Object


45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
# File 'lib/rex/encoder/alpha2/alpha_mixed.rb', line 45

def self.gen_decoder(reg, offset)
  decoder =
     gen_decoder_prefix(reg, offset) +
     "jA" +          # push 0x41
     "X" +           # pop eax
     "P" +           # push eax
     "0A0" +         # xor byte [ecx+30], al
     "A" +           # inc ecx                        <---
     "kAAQ" +        # imul eax, [ecx+42], 51 -> 10       |
     "2AB" +         # xor al, [ecx + 42]                 |
     "2BB" +         # xor al, [edx + 42]                 |
     "0BB" +         # xor [edx + 42], al                 |
     "A" +           # inc ecx                            |
     "B" +           # inc edx                            |
     "X" +           # pop eax                            |
     "P" +           # push eax                           |
     "8AB" +         # cmp [ecx + 42], al                 |
     "uJ" +          # jnz short -------------------------
     "I"             # first encoded char, fixes the above J

  return decoder
end

.gen_decoder_prefix(reg, offset) ⇒ Object


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
# File 'lib/rex/encoder/alpha2/alpha_mixed.rb', line 11

def self.gen_decoder_prefix(reg, offset)
  if (offset > 32)
    raise "Critical: Offset is greater than 32"
  end

  # use inc ebx as a nop here so we still pad correctly
  if (offset <= 16)
    nop = 'C' * offset
    mod = 'I' * (16 - offset) + nop + '7QZ'    # dec ecx,,, push ecx, pop edx
    edxmod = 'J' * (17 - offset)
  else
    mod = 'A' * (offset - 16)
    nop = 'C' * (16 - mod.length)
    mod << nop + '7QZ'
    edxmod = 'B' * (17 - (offset - 16))
  end
  regprefix = {
    'EAX'   => 'PY' + mod,                         # push eax, pop ecx
    'ECX'   => 'I' + mod,                          # dec ecx
    'EDX'   =>  edxmod + nop + '7RY',			   # dec edx,,, push edx, pop ecx
    'EBX'   => 'SY' + mod,                         # push ebx, pop ecx
    'ESP'   => 'TY' + mod,                         # push esp, pop ecx
    'EBP'   => 'UY' + mod,                         # push ebp, pop ecx
    'ESI'   => 'VY' + mod,                         # push esi, pop ecx
    'EDI'   => 'WY' + mod,                         # push edi, pop ecx
  }

  reg.upcase!
  if (not regprefix.keys.include? reg)
    raise ArgumentError.new("Invalid register name")
  end
  return regprefix[reg]
end