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https://github.com/jtesta/ssh-audit.git
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Initial SSH1 support (packet reading, SMSG_PUBLIC_KEY, CRC32, etc) #6.
This commit is contained in:
Andris Raugulis
parent
d6980242ba
commit
9030e71892
254
ssh-audit.py
254
ssh-audit.py
@ -26,8 +26,7 @@
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from __future__ import print_function
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import os, io, sys, socket, struct, random, errno, getopt, re
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VERSION = 'v1.0.20160908'
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SSH_BANNER = 'SSH-2.0-OpenSSH_7.3'
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VERSION = 'v1.0.20160915'
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def usage(err=None):
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@ -142,6 +141,121 @@ class Kex(object):
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return kex
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class SSH1(object):
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class CRC32(object):
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def __init__(self):
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self._table = [0] * 256
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for i in range(256):
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crc = 0
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n = i
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for j in range(8):
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x = (crc ^ n) & 1
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crc = (crc >> 1) ^ (x * 0xedb88320)
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n = n >> 1
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self._table[i] = crc
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def calc(self, v):
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crc, l = 0, len(v)
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for i in range(l):
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n = ord(v[i:i + 1])
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n = n ^ (crc & 0xff)
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crc = (crc >> 8) ^ self._table[n]
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return crc
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_crc32 = CRC32()
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CIPHERS = [None, 'idea', 'des', '3des', 'tss', 'rc4', 'blowfish']
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AUTHS = [None, 'rhosts', 'rsa', 'password', 'rhosts_rsa', 'tis', 'kerberos']
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@classmethod
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def crc32(cls, v):
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return cls._crc32.calc(v)
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class PublicKeyMessage(object):
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def __init__(self, cookie, skey, hkey, pflags, cmask, amask):
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assert len(skey) == 3
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assert len(hkey) == 3
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self.__cookie = cookie
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self.__server_key = skey
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self.__host_key = hkey
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self.__protocol_flags = pflags
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self.__supported_ciphers_mask = cmask
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self.__supported_authentications_mask = amask
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@property
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def cookie(self):
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return self.__cookie
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@property
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def server_key_bits(self):
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return self.__server_key[0]
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@property
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def server_key_public_exponent(self):
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return self.__server_key[1]
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@property
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def server_key_public_modulus(self):
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return self.__server_key[2]
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@property
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def host_key_bits(self):
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return self.__host_key[0]
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@property
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def host_key_public_exponent(self):
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return self.__host_key[1]
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@property
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def host_key_public_modulus(self):
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return self.__host_key[2]
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@property
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def protocol_flags(self):
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return self.__protocol_flags
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@property
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def supported_ciphers_mask(self):
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return self.__supported_ciphers_mask
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@property
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def supported_ciphers(self):
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ciphers = []
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for i in range(len(SSH1.CIPHERS)):
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if self.__supported_ciphers_mask & (1 << i) != 0:
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ciphers.append(SSH1.CIPHERS[i])
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return ciphers
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@property
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def supported_authentications_mask(self):
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return self.__supported_authentications_mask
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@property
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def supported_authentications(self):
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auths = []
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for i in range(len(SSH1.AUTHS)):
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if self.__supported_authentications_mask & (1 << i) != 0:
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auths.append(SSH1.AUTHS[i])
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return auths
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@classmethod
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def parse(cls, payload):
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buf = ReadBuf(payload)
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cookie = buf.read(8)
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server_key_bits = buf.read_int()
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server_key_exponent = buf.read_mpint1()
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server_key_modulus = buf.read_mpint1()
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skey = (server_key_bits, server_key_exponent, server_key_modulus)
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host_key_bits = buf.read_int()
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host_key_exponent = buf.read_mpint1()
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host_key_modulus = buf.read_mpint1()
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hkey = (host_key_bits, host_key_exponent, host_key_modulus)
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pflags = buf.read_int()
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cmask = buf.read_int()
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amask = buf.read_int()
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pkm = cls(cookie, skey, hkey, pflags, cmask, amask)
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return pkm
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class ReadBuf(object):
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def __init__(self, data=None):
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super(ReadBuf, self).__init__()
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@ -269,6 +383,7 @@ class WriteBuf(object):
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class SSH(object):
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class Protocol(object):
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SMSG_PUBLIC_KEY = 2
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MSG_KEXINIT = 20
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MSG_NEWKEYS = 21
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MSG_KEXDH_INIT = 30
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@ -516,6 +631,9 @@ class SSH(object):
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}
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class Socket(ReadBuf, WriteBuf):
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class InsufficientReadException(Exception):
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pass
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SM_BANNER_SENT = 1
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def __init__(self, host, port, cto=3.0, rto=5.0):
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@ -534,7 +652,8 @@ class SSH(object):
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def __enter__(self):
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return self
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def get_banner(self):
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def get_banner(self, sshv=2):
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banner = 'SSH-{0}-OpenSSH_7.3'.format('1.5' if sshv == 1 else '2.0')
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rto = self.__sock.gettimeout()
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self.__sock.settimeout(0.7)
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s, e = self.recv()
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@ -542,7 +661,7 @@ class SSH(object):
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if s < 0:
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return self.__banner, self.__header
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if self.__state < self.SM_BANNER_SENT:
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self.send_banner()
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self.send_banner(banner)
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while self.__banner is None:
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if not s > 0:
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s, e = self.recv()
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@ -586,41 +705,67 @@ class SSH(object):
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return (-1, e)
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self.__sock.send(data)
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def send_banner(self, banner=SSH_BANNER):
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def send_banner(self, banner):
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self.send(banner.encode() + b'\r\n')
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if self.__state < self.SM_BANNER_SENT:
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self.__state = self.SM_BANNER_SENT
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def read_packet(self):
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while self.unread_len < self.__block_size:
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def ensure_read(self, size):
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while self.unread_len < size:
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s, e = self.recv()
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if s < 0:
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if e is None:
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e = self.read(self.unread_len).strip()
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return -1, e
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header = self.read(self.__block_size)
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if len(header) == 0:
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out.fail('[exception] empty ssh packet (no data)')
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sys.exit(1)
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packet_size = struct.unpack('>I', header[:4])[0]
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rest = header[4:]
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lrest = len(rest)
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padding = ord(rest[0:1])
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packet_type = ord(rest[1:2])
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if (packet_size - lrest) % self.__block_size != 0:
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out.fail('[exception] invalid ssh packet (block size)')
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sys.exit(1)
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rlen = packet_size - lrest
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while self.unread_len < rlen:
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s, e = self.recv()
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if s < 0:
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if e is None:
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e = (header + self.read(self.unread_len)).strip()
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return -1, e
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buf = self.read(rlen)
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packet = rest[2:] + buf[0:packet_size - lrest]
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payload = packet[0:packet_size - padding]
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return packet_type, payload
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raise SSH.Socket.InsufficientReadException(e)
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def read_packet(self, sshv=2):
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try:
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header = WriteBuf()
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self.ensure_read(4)
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packet_length = self.read_int()
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header.write_int(packet_length)
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# XXX: validate length
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if sshv == 1:
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padding_length = (8 - packet_length % 8)
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self.ensure_read(padding_length)
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padding = self.read(padding_length)
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header.write(padding)
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payload_length = packet_length
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check_size = padding_length + payload_length
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else:
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self.ensure_read(1)
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padding_length = self.read_byte()
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header.write_byte(padding_length)
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payload_length = packet_length - padding_length - 1
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check_size = 4 + 1 + payload_length + padding_length
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if check_size % self.__block_size != 0:
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out.fail('[exception] invalid ssh packet (block size)')
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sys.exit(1)
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self.ensure_read(payload_length)
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if sshv == 1:
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payload = self.read(payload_length - 4)
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header.write(payload)
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crc = self.read_int()
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header.write_int(crc)
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else:
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payload = self.read(payload_length)
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header.write(payload)
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packet_type = ord(payload[0:1])
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if sshv == 1:
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rcrc = SSH1.crc32(padding + payload)
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if crc != rcrc:
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out.fail('[exception] packet checksum CRC32 mismatch.')
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sys.exit(1)
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else:
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self.ensure_read(padding_length)
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padding = self.read(padding_length)
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payload = payload[1:]
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return packet_type, payload
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except SSH.Socket.InsufficientReadException as ex:
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if ex.args[0] is None:
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header.write(self.read(self.unread_len))
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e = header.write_flush().strip()
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else:
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e = ex.args[0]
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return (-1, e)
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def send_packet(self):
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payload = self.write_flush()
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@ -961,13 +1106,14 @@ def output_security(banner, padlen):
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out.sep()
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def output(banner, header, kex):
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def output(banner, header, kex=None, pkm=None):
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sshv = 1 if pkm else 2
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with OutputBuffer() as obuf:
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if len(header) > 0:
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out.info('(gen) header: ' + '\n'.join(header))
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if banner is not None:
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out.good('(gen) banner: {0}'.format(banner))
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if banner.protocol[0] == 1:
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if sshv == 1 or banner.protocol[0] == 1:
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out.fail('(gen) protocol SSH1 enabled')
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software = SSH.Software.parse(banner)
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if software is not None:
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@ -1045,26 +1191,44 @@ def parse_args():
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return host, port
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def main():
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host, port = parse_args()
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def audit(host, port, sshv=2):
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s = SSH.Socket(host, port)
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err = None
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banner, header = s.get_banner()
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banner, header = s.get_banner(sshv)
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if banner is None:
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err = '[exception] did not receive banner.'
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if err is None:
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packet_type, payload = s.read_packet()
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packet_type, payload = s.read_packet(sshv)
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if packet_type < 0:
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if payload == b'Protocol major versions differ.':
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if sshv == 2:
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audit(host, port, 1)
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return
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err = '[exception] error reading packet ({0})'.format(payload)
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elif packet_type != SSH.Protocol.MSG_KEXINIT:
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err = '[exception] did not receive MSG_KEXINIT (20), ' + \
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'instead received unknown message ({0})'.format(packet_type)
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else:
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if sshv == 1 and packet_type != SSH.Protocol.SMSG_PUBLIC_KEY:
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err = ('SMSG_PUBLIC_KEY', SSH.Protocol.SMSG_PUBLIC_KEY)
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elif sshv == 2 and packet_type != SSH.Protocol.MSG_KEXINIT:
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err = ('MSG_KEXINIT', SSH.Protocol.MSG_KEXINIT)
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if err is not None:
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fmt = '[exception] did not receive {0} ({1}), ' + \
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'instead received unknown message ({2})'
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err = fmt.format(err[0], err[1], packet_type)
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if err:
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output(banner, header, None)
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output(banner, header)
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out.fail(err)
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sys.exit(1)
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kex = Kex.parse(payload)
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output(banner, header, kex)
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if sshv == 1:
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pkm = SSH1.PublicKeyMessage.parse(payload)
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output(banner, header, pkm=pkm)
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elif sshv == 2:
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kex = Kex.parse(payload)
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output(banner, header, kex=kex)
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def main():
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host, port = parse_args()
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audit(host, port)
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if __name__ == '__main__':
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