Add support for dropbear sshd:

- send client banner first
- use data read in first chunk (buffer data)

ssh-audit.py

@@ -77,36 +77,64 @@ class Kex(object):
 	@classmethod
 	def parse(cls, payload):
 		kex = cls()
-		buf = io.BytesIO(payload)
-		kex.cookie = buf.read(16)
-		kex.kex_algorithms = read_list(buf)
-		kex.key_algorithms = read_list(buf)
-		kex.client.encryption = read_list(buf)
-		kex.server.encryption = read_list(buf)
-		kex.client.mac = read_list(buf)
-		kex.server.mac = read_list(buf)
-		kex.client.compression = read_list(buf)
-		kex.server.compression = read_list(buf)
-		kex.client.languages = read_list(buf)
-		kex.server.languages = read_list(buf)
-		kex.follows = read_bool(buf)
-		kex.unused = read_int(buf)
+		buf = ReadBuf(payload)
+		kex.cookie = buf.read_raw(16)
+		kex.kex_algorithms = buf.read_list()
+		kex.key_algorithms = buf.read_list()
+		kex.client.encryption = buf.read_list()
+		kex.server.encryption = buf.read_list()
+		kex.client.mac = buf.read_list()
+		kex.server.mac = buf.read_list()
+		kex.client.compression = buf.read_list()
+		kex.server.compression = buf.read_list()
+		kex.client.languages = buf.read_list()
+		kex.server.languages = buf.read_list()
+		kex.follows = buf.read_bool()
+		kex.unused = buf.read_int()
 		return kex
 
-def read_int(buf):
-	return struct.unpack('>I', buf.read(4))[0]
+class ReadBuf(object):
+	def __init__(self, data = None):
+		self._buf = io.BytesIO(data) if data else io.BytesIO()
+		self._len = len(data) if data else 0
 	
-def read_bool(buf):
-	return struct.unpack('b', buf.read(1))[0] != 0
+	@property
+	def unread_len(self):
+		return self._len - self._buf.tell()
+	
+	def read_raw(self, size):
+		return self._buf.read(size)
+	
+	def read_line(self):
+		return self._buf.readline().rstrip().decode('utf-8')
+	
+	def read_int(self):
+		return struct.unpack('>I', self._buf.read(4))[0]
+	
+	def read_bool(self):
+		return struct.unpack('b', self._buf.read(1))[0] != 0
+	
+	def read_list(self):
+		list_size = self.read_int()
+		return self._buf.read(list_size).decode().split(',')
+
+class SockBuf(ReadBuf):
+	def __init__(self, s):
+		super(SockBuf, self).__init__()
+		self.__sock = s
+	
+	def recv(self, size = 2048):
+		data = self.__sock.recv(size)
+		pos = self._buf.tell()
+		self._buf.seek(0, 2)
+		self._buf.write(data)
+		self._len += len(data)
+		self._buf.seek(pos, 0)
 
-def read_list(buf):
-	list_size = read_int(buf)
-	return buf.read(list_size).decode().split(',')
 
 def get_ssh_ver(v):
 	return 'available since OpenSSH {0}'.format(v)
 
-
 WARN_OPENSSH72_LEGACY = 'removed (in client) since OpenSSH 7.2, legacy algorithm'
 WARN_OPENSSH70_LEGACY = 'removed since OpenSSH 7.0, legacy algorithm'
 FAIL_OPENSSH70_WEAK   = 'removed (in server) and disabled (in client) since OpenSSH 7.0, weak algorithm'
@@ -246,9 +274,9 @@ def process_kex(kex):
 	process_algorithms('mac', kex.server.mac, maxlen)
 	out.sep()
 
-def read_ssh_packet(s):
+def read_ssh_packet(sbuf):
 	block_size = 8
-	header = s.recv(block_size)
+	header = sbuf.read_raw(block_size)
 	packet_size = struct.unpack('>I', header[:4])[0]
 	rest = header[4:]
 	lrest = len(rest)
@@ -257,7 +285,7 @@ def read_ssh_packet(s):
 	if (packet_size - lrest) % block_size != 0:
 		out.fail('[exception] invalid ssh packet (block size)')
 		sys.exit(1)
-	buf = s.recv(packet_size - lrest)
+	buf = sbuf.read_raw(packet_size - lrest)
 	packet = rest[2:] + buf[0:packet_size - lrest]
 	payload = packet[0:packet_size - padding]
 	return packet_type, payload
@@ -291,13 +319,17 @@ def main():
 	try:
 		s = socket.create_connection((host, port), SOCK_CONN_TIMEOUT)
 		s.settimeout(SOCK_READ_TIMEOUT)
-		banner = s.recv(1024).strip()
-		out.head('# general')
-		out.good('[info] banner: ' + banner.decode())
-		if banner.decode().startswith('SSH-1.99-'):
-			out.fail('[fail] protocol SSH1 enabled')
+		sbuf = SockBuf(s)
 		s.send(SSH_BANNER.encode() + b'\r\n')
-		packet_type, payload = read_ssh_packet(s)
+		sbuf.recv()
+		banner = sbuf.read_line()
+		out.head('# general')
+		out.good('[info] banner: ' + banner)
+		if banner.startswith('SSH-1.99-'):
+			out.fail('[fail] protocol SSH1 enabled')
+		if sbuf.unread_len == 0:
+			sbuf.recv()
+		packet_type, payload = read_ssh_packet(sbuf)
 		if packet_type != 20:
 			out.fail('[exception] did not receive MSG_KEXINIT (20), instead received unknown message ({0})'.format(packet_type))
 			sys.exit(1)