def udp_decoder():
manager = AuditManager()
conf = manager.get_configuration(UDP_NAME)
checksum_check = conf['checksum_check']
def udp(mpkt):
mpkt.l4_len = UDP_LENGTH
mpkt.l4_src, \
mpkt.l4_dst = mpkt.get_fields('udp', ('sport', 'dport'))
load = mpkt.get_field('udp')[mpkt.l4_len:]
if load:
mpkt.data = load
if checksum_check:
udpraw = mpkt.get_field('udp')
if udpraw:
if mpkt.payload_len == len(udpraw):
psdhdr = pack("!4s4sHH",
inet_aton(mpkt.l3_src),
inet_aton(mpkt.l3_dst),
mpkt.l4_proto,
mpkt.payload_len)
chksum = checksum(psdhdr + udpraw[:6] + \
'\x00\x00' + udpraw[8:])
if mpkt.get_field('udp.chksum') != chksum:
mpkt.set_cfield('good_checksum', hex(chksum))
manager.user_msg(
_("Invalid UDP packet from %s to %s : " \
"wrong checksum %s instead of %s") % \
(mpkt.l3_src, mpkt.l3_dst, \
hex(mpkt.get_field('udp.chksum', 0)), \
hex(chksum)), \
5, UDP_NAME)
manager.run_decoder(APP_LAYER, PL_DEFAULT, mpkt)
if mpkt.flags & MPKT_MODIFIED and \
mpkt.flags & MPKT_FORWARDABLE:
mpkt.set_field('udp.chksum', None)
return None
return udp
def udp_decoder():
manager = AuditManager()
conf = manager.get_configuration(UDP_NAME)
checksum_check = conf['checksum_check']
def udp(mpkt):
mpkt.l4_len = UDP_LENGTH
mpkt.l4_src, \
mpkt.l4_dst = mpkt.get_fields('udp', ('sport', 'dport'))
load = mpkt.get_field('udp')[mpkt.l4_len:]
if load:
mpkt.data = load
if checksum_check:
udpraw = mpkt.get_field('udp')
if udpraw:
if mpkt.payload_len == len(udpraw):
psdhdr = pack("!4s4sHH", inet_aton(mpkt.l3_src),
inet_aton(mpkt.l3_dst), mpkt.l4_proto,
mpkt.payload_len)
chksum = checksum(psdhdr + udpraw[:6] + \
'\x00\x00' + udpraw[8:])
if mpkt.get_field('udp.chksum') != chksum:
mpkt.set_cfield('good_checksum', hex(chksum))
manager.user_msg(
_("Invalid UDP packet from %s to %s : " \
"wrong checksum %s instead of %s") % \
(mpkt.l3_src, mpkt.l3_dst, \
hex(mpkt.get_field('udp.chksum', 0)), \
hex(chksum)), \
5, UDP_NAME)
manager.run_decoder(APP_LAYER, PL_DEFAULT, mpkt)
if mpkt.flags & MPKT_MODIFIED and \
mpkt.flags & MPKT_FORWARDABLE:
mpkt.set_field('udp.chksum', None)
return None
return udp
def icmp_decoder():
manager = AuditManager()
conf = manager.get_configuration('decoder.icmp')
checksum_check = conf['checksum_check']
def icmp(mpkt):
if not checksum_check:
return None
if mpkt.get_field('ip.flags', 0) & 1:
# Only a fragment
return None
payload = mpkt.cfields.get('reassembled_payload', None)
if not payload:
payload = mpkt.get_field('icmp')
if not payload:
return None
cur_chksum = hex(unpack("!H", payload[2:4])[0])
icmpraw = payload[0:2] + '\x00\x00' + payload[4:]
com_chksum = hex(checksum(icmpraw))
if com_chksum != cur_chksum:
mpkt.set_cfield('good_checksum', com_chksum)
manager.user_msg(_("Invalid ICMP packet from %s to %s : " \
"wrong checksum %s instead of %s") % \
(mpkt.get_field('ip.src'), \
mpkt.get_field('ip.dst'), \
cur_chksum, com_chksum),
5, 'decoder.icmp')
return None
return icmp
def icmp_decoder():
manager = AuditManager()
conf = manager.get_configuration('decoder.icmp')
checksum_check = conf['checksum_check']
def icmp(mpkt):
if not checksum_check:
return None
if mpkt.get_field('ip.flags', 0) & 1:
# Only a fragment
return None
payload = mpkt.cfields.get('reassembled_payload', None)
if not payload:
payload = mpkt.get_field('icmp')
if not payload:
return None
cur_chksum = hex(unpack("!H", payload[2:4])[0])
icmpraw = payload[0:2] + '\x00\x00' + payload[4:]
com_chksum = hex(checksum(icmpraw))
if com_chksum != cur_chksum:
mpkt.set_cfield('good_checksum', com_chksum)
manager.user_msg(_("Invalid ICMP packet from %s to %s : " \
"wrong checksum %s instead of %s") % \
(mpkt.get_field('ip.src'), \
mpkt.get_field('ip.dst'), \
cur_chksum, com_chksum),
5, 'decoder.icmp')
return None
return icmp
def ip_decoder():
manager = AuditManager()
conf = manager.get_configuration('decoder.ip')
checksum_check, reassemble, max_len, max_frags = \
conf['checksum_check'], conf['reassemble'], \
conf['reassemble_max_fraglist'], conf['reassemble_max_fragments']
reas_dict = {}
def ip_reassemble(mpkt):
# Here we have to check for fragmentation
# by creating a dict to holds id of ip packets
# and set mpkt.lock() on it if mpkg is MF
# until the resegmentation is done.
# If it's a fragment we have to return None
# to break the chain.
# TODO: check ip.flags standard name in UMPA
ts = time.time()
mf = mpkt.get_field('ip.flags', 0) & 1
frag_off = mpkt.get_field('ip.frag', 0) * 8
if not mf and frag_off == 0:
return False
ipid = mpkt.get_field('ip.id')
if ipid in reas_dict:
plist = reas_dict[ipid]
if len(plist) >= max_frags:
del reas_dict[ipid]
manager.user_msg(_('Dropping out the sequence with ID: '
'%s due reassemble_max_fragments') %
ipid, 7, 'decoder.ip')
return False
ret = 0
idx = 0
inserted = False
while idx < len(plist):
ts2, frag_off2, mpkt2 = plist[idx]
if frag_off2 == frag_off:
plist[idx] = (ts, frag_off, mpkt.copy())
break
elif frag_off2 < frag_off:
ret += frag_off2
idx += 1
continue
inserted = True
plist.insert(idx, (ts, frag_off, mpkt.copy()))
break
if not inserted:
plist.append((ts, frag_off, mpkt.copy()))
# Now let's get the last packet and see if MF = 0
# EVASION!
if plist[-1][-1].get_field('ip.flags') & 1 == 0:
if idx == len(plist) -1:
ret = frag_off - ret
else:
while idx < len(plist) - 1:
ts2, frag_off2, mpkt2 = plist[idx]
ret += frag_off2
idx += 1
ret = plist[-1][1] - ret
if ret == 0:
log.debug('Reassembling sequence with ID: %s' % \
ipid)
reas_payload = ''
for ts2, frag_off2, mpkt2 in plist:
try:
ihl = mpkt2.l3_len
reas_payload += mpkt2.get_field('ip')[ihl:]
except:
pass
# Ok check that we have a complete payload
ihl = mpkt.l3_len
p_len = frag_off + mpkt.get_field('ip.len') - ihl
if len(reas_payload) != p_len:
mpkt.set_cfield('reassembled_payload', None)
manager.user_msg(_('Reassemble of IP packet ' \
'from %s to %s failed') % \
(mpkt.l3_src, mpkt.l3_dst), \
4, 'decoder.ip')
# Nice drop out everythin!
del reas_dict[ipid]
mpkt.set_cfield('reassembled_payload', reas_payload)
return True
else:
if len(reas_dict) >= max_len:
# Ok just drop the list with the minor ts (the oldest)
min_k = min([(v, k) for k, v in reas_dict.items()])[1]
del reas_dict[min_k]
# Debug
manager.user_msg(_('Dropping out the oldest sequence '
'with ID: %s') % min_k,
7, 'decoder.ip')
log.debug('First packet of the sequence with ID: %s' % ipid)
reas_dict[ipid] = [(ts, frag_off, mpkt)]
return False
def ip(mpkt):
mpkt.l3_src, \
mpkt.l3_dst, \
mpkt.l4_proto = mpkt.get_fields('ip', ('src', 'dst', 'proto'))
# TODO: handle IPv6
ipraw = mpkt.get_field('ip')
if not ipraw:
return
mpkt.l3_len = mpkt.get_field('ip.ihl') * 4
mpkt.payload_len = mpkt.get_field('ip.len') - mpkt.l3_len
if mpkt.context:
mpkt.context.check_forwarded(mpkt)
if mpkt.flags & MPKT_FORWARDED:
return None
mpkt.context.set_forwardable(mpkt)
iplen = min(20, len(ipraw))
if mpkt.get_field('ip.len') > len(ipraw):
# Probably we are capturing with low snaplen
# so the packets are not fully captured. Avoid
# further calculation.
return PROTO_LAYER, mpkt.l4_proto
if checksum_check:
ihl = max(20, mpkt.l3_len)
pkt = ipraw[:10] + '\x00\x00' + ipraw[12:ihl]
chksum = checksum(pkt)
# Probably here it's better to set also a cfield
# and to turn False the checksum_check default value
if mpkt.get_field('ip.chksum') != chksum:
mpkt.set_cfield('good_checksum', hex(chksum))
manager.user_msg(_("Invalid IP packet from %s to %s : " \
"wrong checksum %s instead of %s") % \
(mpkt.l3_src, mpkt.l3_dst, \
hex(mpkt.get_field('ip.chksum')), \
hex(chksum)),
5, 'decoder.ip')
elif reassemble:
ip_reassemble(mpkt)
ident = IPIdent.create(mpkt)
sess = SessionManager().get_session(ident)
if not sess:
sess = Session(ident)
sess.data = IPStatus()
SessionManager().put_session(sess)
sess.prev = mpkt.session
mpkt.session = sess
status = sess.data
status.last_id = mpkt.get_field('ip.id', 0)
manager.run_decoder(PROTO_LAYER, mpkt.l4_proto, mpkt)
if mpkt.flags & MPKT_DROPPED:
status.id_adj -= 1
elif mpkt.flags & MPKT_MODIFIED or status.id_adj != 0:
mpkt.set_field('ip.id', mpkt.get_field('ip.id', 0) + status.id_adj)
mpkt.set_field('ip.len', mpkt.get_field('ip.len', 0) + mpkt.inj_delta)
mpkt.set_field('ip.chksum', None)
return ip
class TCPDecoder(Plugin, PassiveAudit):
def start(self, reader):
self.checksum_check = True
self.reassembler = None
self.manager = None
def stop(self):
manager = AuditManager()
manager.remove_decoder(PROTO_LAYER, NL_TYPE_TCP, self._process_tcp)
manager.remove_injector(1, NL_TYPE_TCP, self._inject_tcp)
try:
manager.remove_decoder_hook(PROTO_LAYER, NL_TYPE_ICMP,
self.reassembler.process_icmp, 1)
except:
pass
def register_decoders(self):
self.manager = AuditManager()
conf = self.manager.get_configuration('decoder.tcp')
self.checksum_check = conf['checksum_check']
self.manager.add_decoder(PROTO_LAYER, NL_TYPE_TCP, self._process_tcp)
self.manager.add_injector(1, NL_TYPE_TCP, self._inject_tcp)
if conf['enable_reassemble']:
self.reassembler = Reassembler(conf['reassemble_workarounds'],
conf['reassemble_maxstreams'])
self.manager.add_decoder_hook(PROTO_LAYER, NL_TYPE_ICMP,
self.reassembler.process_icmp, 1)
def _inject_tcp(self, context, mpkt, length):
"""
Function that manages injection of fragments in active TCP connection
"""
ident = TCPIdent.create(mpkt)
sess = SessionManager().get_session(ident)
if not sess:
log.debug("No TCP session found.")
return False, length
if ident.l3_src == sess.ident.l3_src:
status = sess.data[1]
ostatus = sess.data[0]
else:
status = sess.data[0]
ostatus = sess.data[1]
mpkt.set_fields('tcp', {
'sport' : mpkt.l4_src,
'dport' : mpkt.l4_dst,
'dataofs' : 5,
'chksum' : None,
'urgptr' : 0,
'flags' : TH_PSH,
'options' : {}})
if status.injectable & INJ_FIN or \
not status.injectable & INJ_FWD or \
not ostatus.injectable & INJ_FWD:
log.debug("Session is not injectable.")
return False, length
mpkt.set_fields('tcp', {
'seq' : status.last_seq + status.seq_adj,
'ack' : status.last_ack - ostatus.seq_adj})
if status.last_ack != 0:
mpkt.set_field('tcp.flags', mpkt.l4_flags | TH_ACK)
mpkt.session = sess.prev
length += 20 + mpkt.l2_len
injector = AuditManager().get_injector(0, mpkt.session.ident.magic)
is_ok, length = injector(context, mpkt, length)
if not is_ok:
return is_ok, length
length = context.get_mtu() - length
if length > mpkt.inject_len:
length = mpkt.inject_len
payload = mpkt.inject[:length]
payload_pkt = MetaPacket.new('raw')
payload_pkt.set_field('raw.load', payload)
mpkt.add_to('tcp', payload_pkt)
status.seq_adj += length
mpkt.data_len = length
return True, length
def _process_tcp(self, mpkt):
mpkt.l4_src, \
mpkt.l4_dst, \
mpkt.l4_ack, \
mpkt.l4_seq, \
mpkt.l4_flags = mpkt.get_fields('tcp', ('sport', 'dport', 'ack', \
'seq', 'flags'))
mpkt.l4_len = mpkt.get_field('tcp.dataofs', 5) * 4
if mpkt.l4_src is None:
return None
tcpraw = mpkt.get_field('tcp')
if tcpraw:
mpkt.data_len = mpkt.payload_len - mpkt.l4_len
mpkt.data = tcpraw[mpkt.l4_len:]
wrong = False
if self.checksum_check and tcpraw:
if mpkt.payload_len == len(tcpraw):
ip_src = mpkt.l3_src
ip_dst = mpkt.l3_dst
psdhdr = pack("!4s4sHH",
inet_aton(ip_src),
inet_aton(ip_dst),
mpkt.l4_proto,
mpkt.payload_len)
chksum = checksum(psdhdr + tcpraw[:16] + \
"\x00\x00" + tcpraw[18:])
if mpkt.get_field('tcp.chksum', 0) != chksum:
wrong = True
mpkt.set_cfield('good_checksum', hex(chksum))
self.manager.user_msg(
_("Invalid TCP packet from %s to %s : " \
"wrong checksum %s instead of %s") % \
(ip_src, ip_dst, \
hex(mpkt.get_field('tcp.chksum', 0)), \
hex(chksum)),
5, 'decoder.tcp')
if wrong:
self.manager.run_decoder(APP_LAYER, PL_DEFAULT, mpkt)
return None
if self.reassembler:
self.reassembler.process_tcp(mpkt)
ident = TCPIdent.create(mpkt)
sess = SessionManager().get_session(ident)
if not sess:
sess = Session(ident)
sess.data = (TCPStatus(), TCPStatus())
SessionManager().put_session(sess)
sess.prev = mpkt.session
mpkt.session = sess
if ident.l3_src == sess.ident.l3_src:
status = sess.data[1]
ostatus = sess.data[0]
else:
status = sess.data[0]
ostatus = sess.data[1]
status.last_seq = mpkt.l4_seq + mpkt.data_len
if mpkt.l4_flags & TH_ACK:
status.last_ack = mpkt.l4_ack
if mpkt.l4_flags & TH_SYN:
status.last_seq += 1
if mpkt.l4_flags & TH_RST:
status.injectable |= INJ_FIN
ostatus.injectable |= INJ_FIN
if mpkt.flags & MPKT_FORWARDABLE:
status.injectable |= INJ_FWD
elif status.injectable & INJ_FWD:
status.injectable ^= INJ_FWD
self.manager.run_decoder(APP_LAYER, PL_DEFAULT, mpkt)
if mpkt.l4_flags & TH_FIN:
status.injectable |= INJ_FIN
if mpkt.flags & MPKT_DROPPED and mpkt.flags & MPKT_FORWARDABLE:
status.seq_adj += mpkt.inj_delta
elif (mpkt.flags & MPKT_MODIFIED or \
status.seq_adj != 0 or ostatus != 0) and \
mpkt.flags & MPKT_FORWARDABLE:
mpkt.set_field('tcp.seq', mpkt.l4_seq + status.seq_adj)
mpkt.set_field('tcp.ack', mpkt.l4_ack - ostatus.seq_adj)
status.seq_adj += mpkt.inj_delta
mpkt.set_field('tcp.chksum', None)
return None
def ip_decoder():
manager = AuditManager()
conf = manager.get_configuration('decoder.ip')
checksum_check, reassemble, max_len, max_frags = \
conf['checksum_check'], conf['reassemble'], \
conf['reassemble_max_fraglist'], conf['reassemble_max_fragments']
reas_dict = {}
def ip_reassemble(mpkt):
# Here we have to check for fragmentation
# by creating a dict to holds id of ip packets
# and set mpkt.lock() on it if mpkg is MF
# until the resegmentation is done.
# If it's a fragment we have to return None
# to break the chain.
# TODO: check ip.flags standard name in UMPA
ts = time.time()
mf = mpkt.get_field('ip.flags', 0) & 1
frag_off = mpkt.get_field('ip.frag', 0) * 8
if not mf and frag_off == 0:
return False
ipid = mpkt.get_field('ip.id')
if ipid in reas_dict:
plist = reas_dict[ipid]
if len(plist) >= max_frags:
del reas_dict[ipid]
manager.user_msg(
_('Dropping out the sequence with ID: '
'%s due reassemble_max_fragments') % ipid, 7,
'decoder.ip')
return False
ret = 0
idx = 0
inserted = False
while idx < len(plist):
ts2, frag_off2, mpkt2 = plist[idx]
if frag_off2 == frag_off:
plist[idx] = (ts, frag_off, mpkt.copy())
break
elif frag_off2 < frag_off:
ret += frag_off2
idx += 1
continue
inserted = True
plist.insert(idx, (ts, frag_off, mpkt.copy()))
break
if not inserted:
plist.append((ts, frag_off, mpkt.copy()))
# Now let's get the last packet and see if MF = 0
# EVASION!
if plist[-1][-1].get_field('ip.flags') & 1 == 0:
if idx == len(plist) - 1:
ret = frag_off - ret
else:
while idx < len(plist) - 1:
ts2, frag_off2, mpkt2 = plist[idx]
ret += frag_off2
idx += 1
ret = plist[-1][1] - ret
if ret == 0:
log.debug('Reassembling sequence with ID: %s' % \
ipid)
reas_payload = ''
for ts2, frag_off2, mpkt2 in plist:
try:
ihl = mpkt2.l3_len
reas_payload += mpkt2.get_field('ip')[ihl:]
except:
pass
# Ok check that we have a complete payload
ihl = mpkt.l3_len
p_len = frag_off + mpkt.get_field('ip.len') - ihl
if len(reas_payload) != p_len:
mpkt.set_cfield('reassembled_payload', None)
manager.user_msg(_('Reassemble of IP packet ' \
'from %s to %s failed') % \
(mpkt.l3_src, mpkt.l3_dst), \
4, 'decoder.ip')
# Nice drop out everythin!
del reas_dict[ipid]
mpkt.set_cfield('reassembled_payload', reas_payload)
return True
else:
if len(reas_dict) >= max_len:
# Ok just drop the list with the minor ts (the oldest)
min_k = min([(v, k) for k, v in reas_dict.items()])[1]
del reas_dict[min_k]
# Debug
manager.user_msg(
_('Dropping out the oldest sequence '
'with ID: %s') % min_k, 7, 'decoder.ip')
log.debug('First packet of the sequence with ID: %s' % ipid)
reas_dict[ipid] = [(ts, frag_off, mpkt)]
return False
def ip(mpkt):
mpkt.l3_src, \
mpkt.l3_dst, \
mpkt.l4_proto = mpkt.get_fields('ip', ('src', 'dst', 'proto'))
# TODO: handle IPv6
ipraw = mpkt.get_field('ip')
if not ipraw:
return
mpkt.l3_len = mpkt.get_field('ip.ihl') * 4
mpkt.payload_len = mpkt.get_field('ip.len') - mpkt.l3_len
if mpkt.context:
mpkt.context.check_forwarded(mpkt)
if mpkt.flags & MPKT_FORWARDED:
return None
mpkt.context.set_forwardable(mpkt)
iplen = min(20, len(ipraw))
if mpkt.get_field('ip.len') > len(ipraw):
# Probably we are capturing with low snaplen
# so the packets are not fully captured. Avoid
# further calculation.
return PROTO_LAYER, mpkt.l4_proto
if checksum_check:
ihl = max(20, mpkt.l3_len)
pkt = ipraw[:10] + '\x00\x00' + ipraw[12:ihl]
chksum = checksum(pkt)
# Probably here it's better to set also a cfield
# and to turn False the checksum_check default value
if mpkt.get_field('ip.chksum') != chksum:
mpkt.set_cfield('good_checksum', hex(chksum))
manager.user_msg(_("Invalid IP packet from %s to %s : " \
"wrong checksum %s instead of %s") % \
(mpkt.l3_src, mpkt.l3_dst, \
hex(mpkt.get_field('ip.chksum')), \
hex(chksum)),
5, 'decoder.ip')
elif reassemble:
ip_reassemble(mpkt)
ident = IPIdent.create(mpkt)
sess = SessionManager().get_session(ident)
if not sess:
sess = Session(ident)
sess.data = IPStatus()
SessionManager().put_session(sess)
sess.prev = mpkt.session
mpkt.session = sess
status = sess.data
status.last_id = mpkt.get_field('ip.id', 0)
manager.run_decoder(PROTO_LAYER, mpkt.l4_proto, mpkt)
if mpkt.flags & MPKT_DROPPED:
status.id_adj -= 1
elif mpkt.flags & MPKT_MODIFIED or status.id_adj != 0:
mpkt.set_field('ip.id', mpkt.get_field('ip.id', 0) + status.id_adj)
mpkt.set_field('ip.len',
mpkt.get_field('ip.len', 0) + mpkt.inj_delta)
mpkt.set_field('ip.chksum', None)
return ip
