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record_sslv2.py
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record_sslv2.py
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# SPDX-License-Identifier: GPL-2.0-only
# This file is part of Scapy
# See https://scapy.net/ for more information
# Copyright (C) 2017 Maxence Tury
"""
SSLv2 Record.
"""
import struct
from scapy.config import conf
from scapy.error import log_runtime
from scapy.compat import orb, raw
from scapy.packet import Raw
from scapy.layers.tls.session import _GenericTLSSessionInheritance
from scapy.layers.tls.record import _TLSMsgListField, TLS
from scapy.layers.tls.handshake_sslv2 import _sslv2_handshake_cls
from scapy.layers.tls.basefields import (_SSLv2LengthField, _SSLv2PadField,
_SSLv2PadLenField, _TLSMACField)
###############################################################################
# SSLv2 Record Protocol #
###############################################################################
class _SSLv2MsgListField(_TLSMsgListField):
def __init__(self, name, default, length_from=None):
if not length_from:
length_from = lambda pkt: ((pkt.len & 0x7fff) -
(pkt.padlen or 0) -
len(pkt.mac))
super(_SSLv2MsgListField, self).__init__(name, default,
length_from=length_from)
def m2i(self, pkt, m):
cls = Raw
if len(m) >= 1:
msgtype = orb(m[0])
cls = _sslv2_handshake_cls.get(msgtype, Raw)
if cls is Raw:
return Raw(m)
else:
return cls(m, tls_session=pkt.tls_session)
def i2m(self, pkt, p):
cur = b""
if isinstance(p, _GenericTLSSessionInheritance):
p.tls_session = pkt.tls_session
if not pkt.tls_session.frozen:
cur = p.raw_stateful()
p.post_build_tls_session_update(cur)
else:
cur = raw(p)
else:
cur = raw(p)
return cur
def addfield(self, pkt, s, val):
res = b""
for p in val:
res += self.i2m(pkt, p)
return s + res
class SSLv2(TLS):
"""
The encrypted_data is the encrypted version of mac+msg+pad.
"""
__slots__ = ["with_padding", "protected_record"]
name = "SSLv2"
fields_desc = [_SSLv2LengthField("len", None),
_SSLv2PadLenField("padlen", None),
_TLSMACField("mac", b""),
_SSLv2MsgListField("msg", []),
_SSLv2PadField("pad", "")]
def __init__(self, *args, **kargs):
self.with_padding = kargs.get("with_padding", False)
self.protected_record = kargs.get("protected_record", None)
super(SSLv2, self).__init__(*args, **kargs)
# Parsing methods
def _sslv2_mac_verify(self, msg, mac):
secret = self.tls_session.rcs.cipher.key
if secret is None:
return True
mac_len = self.tls_session.rcs.mac_len
if mac_len == 0: # should be TLS_NULL_WITH_NULL_NULL
return True
if len(mac) != mac_len:
return False
read_seq_num = struct.pack("!I", self.tls_session.rcs.seq_num)
alg = self.tls_session.rcs.hash
h = alg.digest(secret + msg + read_seq_num)
return h == mac
def pre_dissect(self, s):
if len(s) < 2:
raise Exception("Invalid record: header is too short.")
msglen = struct.unpack("!H", s[:2])[0]
if msglen & 0x8000:
hdrlen = 2
msglen_clean = msglen & 0x7fff
else:
hdrlen = 3
msglen_clean = msglen & 0x3fff
hdr = s[:hdrlen]
efrag = s[hdrlen:hdrlen + msglen_clean]
self.protected_record = s[:hdrlen + msglen_clean]
r = s[hdrlen + msglen_clean:]
mac = pad = b""
# Decrypt (with implicit IV if block cipher)
mfrag = self._tls_decrypt(efrag)
# Extract MAC
maclen = self.tls_session.rcs.mac_len
if maclen == 0:
mac, pfrag = b"", mfrag
else:
mac, pfrag = mfrag[:maclen], mfrag[maclen:]
# Extract padding
padlen = 0
if hdrlen == 3:
padlen = orb(s[2])
if padlen == 0:
cfrag, pad = pfrag, b""
else:
cfrag, pad = pfrag[:-padlen], pfrag[-padlen:]
# Verify integrity
is_mac_ok = self._sslv2_mac_verify(cfrag + pad, mac)
if not is_mac_ok:
pkt_info = self.firstlayer().summary()
log_runtime.info("SSLv2: record integrity check failed [%s]", pkt_info) # noqa: E501
reconstructed_body = mac + cfrag + pad
return hdr + reconstructed_body + r
def post_dissect(self, s):
"""
SSLv2 may force us to commit the write connState here.
"""
if self.tls_session.triggered_prcs_commit:
if self.tls_session.prcs is not None:
self.tls_session.rcs = self.tls_session.prcs
self.tls_session.prcs = None
self.tls_session.triggered_prcs_commit = False
if self.tls_session.triggered_pwcs_commit:
if self.tls_session.pwcs is not None:
self.tls_session.wcs = self.tls_session.pwcs
self.tls_session.pwcs = None
self.tls_session.triggered_pwcs_commit = False
if self.tls_session.prcs is not None:
self.tls_session.prcs.seq_num += 1
self.tls_session.rcs.seq_num += 1
return s
def do_dissect_payload(self, s):
if s:
try:
p = SSLv2(s, _internal=1, _underlayer=self,
tls_session=self.tls_session)
except KeyboardInterrupt:
raise
except Exception:
if conf.debug_dissector:
raise
p = conf.raw_layer(s, _internal=1, _underlayer=self)
self.add_payload(p)
# Building methods
def _sslv2_mac_add(self, msg):
secret = self.tls_session.wcs.cipher.key
if secret is None:
return msg
write_seq_num = struct.pack("!I", self.tls_session.wcs.seq_num)
alg = self.tls_session.wcs.hash
h = alg.digest(secret + msg + write_seq_num)
return h + msg
def _sslv2_pad(self, s):
padding = b""
block_size = self.tls_session.wcs.cipher.block_size
padlen = block_size - (len(s) % block_size)
if padlen == block_size:
padlen = 0
padding = b"\x00" * padlen
return s + padding
def post_build(self, pkt, pay):
if self.protected_record is not None:
# we do not update the tls_session
return self.protected_record + pay
if self.padlen is None:
cfrag = pkt[2:]
else:
cfrag = pkt[3:]
if self.pad == b"" and self.tls_session.wcs.cipher.type == 'block':
pfrag = self._sslv2_pad(cfrag)
else:
pad = self.pad or b""
pfrag = cfrag + pad
padlen = self.padlen
if padlen is None:
padlen = len(pfrag) - len(cfrag)
hdr = pkt[:2]
if padlen > 0:
hdr += struct.pack("B", padlen)
# Integrity
if self.mac == b"":
mfrag = self._sslv2_mac_add(pfrag)
else:
mfrag = self.mac + pfrag
# Encryption
efrag = self._tls_encrypt(mfrag)
if self.len is not None:
tmp_len = self.len
if not self.with_padding:
tmp_len |= 0x8000
hdr = struct.pack("!H", tmp_len) + hdr[2:]
else:
# Update header with the length of TLSCiphertext.fragment
msglen_new = len(efrag)
if padlen:
if msglen_new > 0x3fff:
raise Exception("Invalid record: encrypted data too long.")
else:
if msglen_new > 0x7fff:
raise Exception("Invalid record: encrypted data too long.")
msglen_new |= 0x8000
hdr = struct.pack("!H", msglen_new) + hdr[2:]
# Now we commit the pending write state if it has been triggered (e.g.
# by an underlying TLSChangeCipherSpec or a SSLv2ClientMasterKey). We
# update nothing if the pwcs was not set. This probably means that
# we're working out-of-context (and we need to keep the default wcs).
# SSLv2 may force us to commit the reading connState here.
if self.tls_session.triggered_pwcs_commit:
if self.tls_session.pwcs is not None:
self.tls_session.wcs = self.tls_session.pwcs
self.tls_session.pwcs = None
self.tls_session.triggered_pwcs_commit = False
if self.tls_session.triggered_prcs_commit:
if self.tls_session.prcs is not None:
self.tls_session.rcs = self.tls_session.prcs
self.tls_session.prcs = None
self.tls_session.triggered_prcs_commit = False
if self.tls_session.pwcs is not None:
self.tls_session.pwcs.seq_num += 1
self.tls_session.wcs.seq_num += 1
return hdr + efrag + pay