Module: Msf::Auxiliary::CRand

Defined in:
lib/msf/core/auxiliary/crand.rb

Overview

This module provides a complete port of the libc rand() and srand() functions. It is used by the NETGEAR WNR2000v5 auxiliary and exploit modules, but might be useful for any other module that needs to emulate C's random number generator.

Author: Pedro Ribeiro ([email protected]) / Agile Information Security

Constant Summary collapse

TYPE_3 =
3
BREAK_3 =
128
DEG_3 =
31
SEP_3 =
3

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#randtblObject

Returns the value of attribute randtbl


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# File 'lib/msf/core/auxiliary/crand.rb', line 14

def randtbl
  @randtbl
end

#unsafe_stateObject

Returns the value of attribute unsafe_state


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# File 'lib/msf/core/auxiliary/crand.rb', line 15

def unsafe_state
  @unsafe_state
end

Instance Method Details

#initialize(info = {}) ⇒ Object


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# File 'lib/msf/core/auxiliary/crand.rb', line 26

def initialize(info = {})
  super

  @randtbl =
  [
    # we omit TYPE_3 from here, not needed
    -1726662223, 379960547, 1735697613, 1040273694, 1313901226,
    1627687941, -179304937, -2073333483, 1780058412, -1989503057,
    -615974602, 344556628, 939512070, -1249116260, 1507946756,
    -812545463, 154635395, 1388815473, -1926676823, 525320961,
    -1009028674, 968117788, -123449607, 1284210865, 435012392,
    -2017506339, -911064859, -370259173, 1132637927, 1398500161,
    -205601318,
  ]

  @unsafe_state = {
    "fptr" => SEP_3,
    "rptr" => 0,
    "state" => 0,
    "rand_type" => TYPE_3,
    "rand_deg" => DEG_3,
    "rand_sep" => SEP_3,
    "end_ptr" => DEG_3
  }
end

#random_rObject

Emulate the behaviour of C's rand


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# File 'lib/msf/core/auxiliary/crand.rb', line 86

def random_r
  buf = @unsafe_state
  state = buf['state']

  fptr = buf['fptr']
  rptr = buf['rptr']
  end_ptr = buf['end_ptr']
  val = @randtbl[fptr] += @randtbl[rptr]

  result = (val >> 1) & 0x7fffffff
  fptr += 1
  if (fptr >= end_ptr)
    fptr = state
    rptr += 1
  else
    rptr += 1
    if (rptr >= end_ptr)
      rptr = state
    end
  end
  buf['fptr'] = fptr
  buf['rptr'] = rptr

  result
end

#srandom_r(seed) ⇒ Object

Emulate the behaviour of C's srand


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# File 'lib/msf/core/auxiliary/crand.rb', line 53

def srandom_r (seed)
  state = @randtbl
  if seed == 0
    seed = 1
  end
  state[0] = seed

  dst = 0
  word = seed
  kc = DEG_3
  for i in 1..(kc-1)
    hi = word / 127773
    lo = word % 127773
    word = 16807 * lo - 2836 * hi
    if (word < 0)
      word += 2147483647
    end
    dst += 1
    state[dst] = word
  end

  @unsafe_state['fptr'] = @unsafe_state['rand_sep']
  @unsafe_state['rptr'] = 0

  kc *= 10
  kc -= 1
  while (kc >= 0)
    random_r
    kc -= 1
  end
end