def handle_ul(self, ipbuf):
# check if we have a TCP SYN
ip_proto, ip_pay = ord(ipbuf[9:10]), ipbuf[20:]
if ip_proto != 6:
# not TCP
return
if ip_pay[13:14] != b'\x02':
# not SYN
return
# build the TCP SYN-ACK: invert src / dst ports, seq num (random),
# ack num (SYN seq num + 1)
tcpsrc, tcpdst, seq = unpack('!HHI', ip_pay[:8])
tcp_synack = TCP(val={
'seq': randint(1, 4294967295),
'ack': (1 + seq) % 4294967296,
'src': tcpdst,
'dst': tcpsrc,
'SYN': 1,
'ACK': 1,
'win': 0x1000
},
hier=1)
# build the IPv4 header: invert src / dst addr
ipsrc, ipdst = inet_ntoa(ipbuf[12:16]), inet_ntoa(ipbuf[16:20])
iphdr = IPv4(val={'src': ipdst, 'dst': ipsrc}, hier=0)
#
pkt = Envelope('p', GEN=(iphdr, tcp_synack))
# send back the TCP SYN-ACK
self.GTPUd.transfer_to_int(pkt.to_bytes())
def handle_ul(self, ipbuf):
# check if we have an UDP/53 request
ip_proto, (udpsrc, udpdst) = ord(ipbuf[9]), unpack('!HH', ipbuf[20:24])
if ip_proto != 17:
# not UDP
return
if udpdst != 53:
# not DNS
return
# build the UDP / DNS response: invert src / dst UDP ports
if self.UDP_CS:
udp = UDP(val={'src': udpdst, 'dst': udpsrc}, hier=1)
else:
udp = UDP(val={'src': udpdst, 'dst': udpsrc, 'cs': 0}, hier=1)
# DNS request: transaction id, flags, questions, queries
dnsreq = ipbuf[28:]
transac_id, questions, queries = dnsreq[0:2], \
unpack('!H', dnsreq[4:6])[0], \
dnsreq[12:]
if questions > 1:
# not supported
self._log('WNG', '%i questions, unsupported' % questions)
# DNS response: transaction id, flags, questions, answer RRs,
# author RRs, add RRs, queries, answers, autor nameservers, add records
if self.RAND:
ip_resp = _urandom(4)
else:
ip_resp = inet_aton(self.IP_RESP)
dnsresp = b''.join(
(transac_id, b'\x81\x80\0\x01\0\x01\0\0\0\0', queries,
b'\xc0\x0c\0\x01\0\x01\0\0\0\x20\0\x04', ip_resp))
# build the IPv4 header: invert src / dst addr
ipsrc, ipdst = inet_ntoa(ipbuf[12:16]), inet_ntoa(ipbuf[16:20])
iphdr = IPv4(val={'src': ipdst, 'dst': ipsrc}, hier=0)
#
pkt = Envelope('p', GEN=(iphdr, udp, Buf('dns', val=dnsresp, hier=2)))
# send back the DNS response
self.GTPUd.transfer_to_int(pkt.to_bytes())
