check_openvpn: Update to ba01f5f
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e5a659f339
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@ -2,10 +2,12 @@
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# Check if an OpenVPN server runs on a given UDP or TCP port.
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#
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# Copyright 2013 Roland Wolters
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# Copyright 2016 Alarig Le Lay
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# (C) 2013, Roland Wolters
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#
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# Version 20160803
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# Contributors:
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# - Andreas Stefl
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# - Alarig Le Lay
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# - Roland Wolters
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#
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# Permission is hereby granted, free of charge, to any person obtaining
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# a copy of this software and associated documentation files (the
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@ -36,92 +38,168 @@ import socket
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import argparse
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import binascii
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HMAC_CLIENT_KEY_START = 192
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P_CONTROL_HARD_RESET_CLIENT_V2 = 7
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P_CONTROL_HARD_RESET_SERVER_V2 = 8
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MAX_P_CONTROL_SIZE = 128 # TODO: adopt
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MAX_CIPHER_KEY_LENGTH = 64
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MAX_HMAC_KEY_LENGTH = 64
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BUFFER_SIZE = 1024
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ALGORITHMS_AVAILABLE = hashlib.algorithms_available \
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if hasattr(hashlib, "algorithms_available") else hashlib.algorithms
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ALGORITHMS_AVAILABLE = hashlib.algorithms_available if hasattr(hashlib, "algorithms_available") else hashlib.algorithms
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def ok(msg):
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print('OK: %s' % msg)
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return 0
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def warning(msg):
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print('WARN: %s' % msg)
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return 1
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def critical(msg):
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print('CRIT: %s' % msg)
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return 2
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def buildpacket(tcp, key, digestmod):
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packet = 1
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ts = int(time.time())
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session = os.urandom(8)
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def build_p_control_hard_reset_client_v2(sid, digest, key):
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# see openvpn source code "src/openvpn/crypto.c" function openvpn_decrypt_v1
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pid = 1 # packet id
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ts = int(time.time()) # net time
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if key:
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# hmac
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h = hmac.new(key, digestmod=digestmod)
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h.update(struct.pack('>I', packet)) # packet id
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# generate hmac
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h = hmac.new(key, digestmod=digest)
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h.update(struct.pack('>I', pid)) # packet id
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h.update(struct.pack('>I', ts)) # net time
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h.update(b'\x38') # type
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h.update(session) # session id
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h.update(struct.pack('>B', P_CONTROL_HARD_RESET_CLIENT_V2 << 3)) # packet type
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h.update(sid) # session id
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h.update(struct.pack('>B', 0)) # message packet id array length
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h.update(struct.pack('>I', 0)) # message packet id
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# packet
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# build packet
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result = b''
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result += b'\x38' # type
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result += session # session id
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result += struct.pack('>B', P_CONTROL_HARD_RESET_CLIENT_V2 << 3) # packet type
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result += sid # session id
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if key: result += h.digest() # hmac
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result += struct.pack('>I', packet) # packet id
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result += struct.pack('>I', ts) # net time
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if key: result += struct.pack('>I', pid) # packet id
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if key: result += struct.pack('>I', ts) # net time
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result += struct.pack('>B', 0) # message packet id array length
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result += struct.pack('>I', 0) # message packet id
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if tcp: result = struct.pack('>H', len(result)) + result
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return result
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def checkserver(host, port, tcp, timeout, key, digest):
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packet = buildpacket(tcp, key, digest)
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check = checkserver_tcp if tcp else checkserver_udp
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return check(host, port, timeout, packet)
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def validate_p_control_hard_reset_server_v2(packet, query_sid, digest, digest_size, key):
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# see openvpn source code "src/openvpn/crypto.c" function openvpn_decrypt_v1
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# identify packet
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if False: pass
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elif len(packet) - struct.unpack('>B', packet[9:10])[0] * 4 == 14: plen = 0 # type sid mpida mpid
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elif len(packet) - struct.unpack('>B', packet[9:10])[0] * 4 == 22: plen = 1 # type sid mpida rsid mpid
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elif len(packet) - struct.unpack('>B', packet[17+digest_size:18+digest_size])[0] * 4 == 30+digest_size: plen = 2 # type sid hmac pid ts mpida rsid mpid
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else: return 20
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# parse packet
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ptype = struct.unpack('>B', packet[:1])[0] # packet type
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packet = packet[1:]
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sid = packet[:8] # session id
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packet = packet[8:]
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if plen >= 2:
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phmac = packet[:digest_size] # hmac
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packet = packet[digest_size:]
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pid = struct.unpack('>I', packet[:4])[0] # packet id
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packet = packet[4:]
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ts = struct.unpack('>I', packet[:4])[0] # net time
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packet = packet[4:]
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mpidlen = struct.unpack('>B', packet[:1])[0] # message packet id array length
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packet = packet[1:]
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mpidarray = [] # packet id array
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for i in range(mpidlen):
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mpidarray.append(struct.unpack('>I', packet[:4])[0]) # message packet id array element
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packet = packet[4:]
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if plen >= 1:
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rsid = packet[:8] # remote session id
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packet = packet[8:]
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mpid = struct.unpack('>I', packet[:4])[0] # message packet id
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# validate packet
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if ptype != P_CONTROL_HARD_RESET_SERVER_V2 << 3: return 20
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if mpid != 0: return 20
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if plen >= 1 and rsid != query_sid: return 20
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if plen >= 2 and key:
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if pid != 1: return 20
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# generate hmac
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h = hmac.new(key, digestmod=digest)
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h.update(struct.pack('>I', pid)) # packet id
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h.update(struct.pack('>I', ts)) # net time
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h.update(struct.pack('>B', ptype)) # packet type
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h.update(sid) # session id
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h.update(struct.pack('>B', mpidlen)) # message packet id array length
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for e in mpidarray: h.update(struct.pack('>I', e)) # message packet id array element
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h.update(rsid) # remote session id
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h.update(struct.pack('>I', mpid)) # message packet id
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if phmac != h.digest(): return 10
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return 1
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return 0
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def check(host, port, tcp, timeout, digest, digest_size, client_key, server_key, retrycount, validate):
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sid = os.urandom(8) # session id
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packet = build_p_control_hard_reset_client_v2(sid, digest, client_key)
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query_server = query_tcp_server if tcp else query_udp_server
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def checkserver_udp(host, port, timeout, packet):
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# thanks to glucas for the idea
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try:
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af, socktype, proto, canonname, sa = socket.getaddrinfo(host, port, \
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socket.AF_UNSPEC, socket.SOCK_DGRAM)[0]
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s = create_socket(host, port, tcp, timeout)
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except socket.error:
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return critical('Unable to create socket')
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try:
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response = query_server(s, host, port, packet, retrycount)
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except RuntimeError:
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return critical('Invalid response')
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except:
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return critical('Not responding')
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finally:
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s.close()
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if response is None:
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return critical('Not responding')
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# for debugging purpose
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# response = binascii.hexlify(response)
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if not validate: return ok('Responded')
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valid = validate_p_control_hard_reset_server_v2(response, sid, digest, digest_size, server_key)
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if valid == 0: return ok('Response validated')
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if valid == 1: return ok('Response validated, checked HMAC')
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if valid == 10: return warning('Invalid HMAC')
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return critical('Invalid response')
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def create_socket(host, port, tcp, timeout):
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# thanks to glucas for the idea
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sock_type = socket.SOCK_STREAM if tcp else socket.SOCK_DGRAM
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af, socktype, proto, canonname, sa = socket.getaddrinfo(host, port, socket.AF_UNSPEC, sock_type)[0]
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s = socket.socket(af, socktype, proto)
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s.settimeout(timeout)
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except socket.error:
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return critical('Unable to create UDP socket')
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return s
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def query_udp_server(s, host, port, packet, retrycount):
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# Send up to 'retrycount' UDP packets with 'timeout' secs between each.
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# Return data after receiving first UDP packet.
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for i in range(retrycount):
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try:
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s.sendto(packet, (host, port))
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# TODO: check response address
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data, _ = s.recvfrom(BUFFER_SIZE)
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reply = binascii.hexlify(data)
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return ok('OpenVPN UDP server response (hex): %s' % reply)
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return data
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except socket.timeout:
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pass
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except:
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return critical('OpenVPN UDP server not responding')
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finally:
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s.close()
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return None
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return None
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def checkserver_tcp(host, port, timeout, packet):
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try:
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af, socktype, proto, canonname, sa = socket.getaddrinfo(host, port, \
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socket.AF_UNSPEC, socket.SOCK_STREAM)[0]
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s = socket.socket(af, socktype, proto)
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s.settimeout(timeout)
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except socket.error:
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return critical('Unable to create TCP socket')
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try:
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def query_tcp_server(s, host, port, packet, retrycount):
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# ignore retrycount
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s.connect((host, port))
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s.send(packet)
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data = s.recv(BUFFER_SIZE)
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if len(data) <= 0: raise RuntimeError
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reply = binascii.hexlify(data)
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return ok('OpenVPN TCP server response (hex): %s' % reply)
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except:
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return critical('OpenVPN TCP server not responding')
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finally:
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s.close()
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s.send(struct.pack('>H', len(packet)) + packet)
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length = struct.unpack('>H', s.recv(2))[0]
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if length > MAX_P_CONTROL_SIZE: raise RuntimeError
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data = s.recv(length)
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if len(data) != length: raise RuntimeError
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return data
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def readkey(path):
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key = None
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@ -135,17 +213,23 @@ def readkey(path):
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return None
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index_start += 2
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key = key[index_start:index_end].replace('\n', '').replace('\r', '')
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key = binascii.unhexlify(key)
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return key
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def optionsparser(argv=None):
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parser = argparse.ArgumentParser()
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parser.add_argument('-p', '--port', help='set port number (default is %(default)d)', type=int, default=1194)
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parser.add_argument('-t', '--tcp', help='use tcp instead of udp', action='store_true')
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parser.add_argument('--timeout', help='set timeout (default is %(default)d)', type=int, default=5)
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parser.add_argument('--digest', help='set HMAC digest (default is "%(default)s")', default='sha1')
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parser.add_argument('--timeout', help='set timeout in seconds, for udp counted per packet (default is %(default)d)', type=int, default=2)
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parser.add_argument('--digest', help='set digest algorithm (default is "%(default)s")', default='sha1')
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parser.add_argument('--digest-size', help='set HMAC digest size', type=int)
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parser.add_argument('--digest-key', help='set HMAC key')
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parser.add_argument('--digest-key-client', help='set client HMAC key')
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parser.add_argument('--digest-key-server', help='set server HMAC key for packet validation')
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parser.add_argument('--tls-auth', help='set tls-auth file')
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# TODO: direction argument (normal, inverse)
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parser.add_argument('--tls-auth-inverse', help='set tls-auth file direction to inverse (1)', action='store_true')
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parser.add_argument('--retrycount', help='number of udp retries before giving up (default is %(default)d)', type=int, default=3)
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parser.add_argument('--no-validation', help='do not validate response', action='store_true')
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parser.add_argument('host', help='the OpenVPN host name or IP')
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return parser.parse_args(argv)
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@ -154,10 +238,13 @@ def main(argv=None):
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if args.digest_size and args.digest_size < 0:
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critical('digest size must be positive')
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if args.tls_auth and args.digest_key:
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if args.retrycount < 1:
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critical('retry count must be positive')
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if args.tls_auth and (args.digest_key_client or args.digest_key_server):
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critical('--tls-auth cannot go with --digest-key')
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key = args.digest_key
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client_key = binascii.unhexlify(args.digest_key_client) if args.digest_key_client else None
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server_key = binascii.unhexlify(args.digest_key_server) if args.digest_key_server else None
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digest = args.digest
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digest_size = args.digest_size
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@ -171,15 +258,22 @@ def main(argv=None):
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return critical('digest creation failed')
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if args.tls_auth:
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# see openvpn source code "src/openvpn/crypto.h", "src/openvpn/crypto.c" and "src/openvpn/crypto_backend.h"
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# 64 byte cipher direction 0, 64 byte hmac direction 0, 64 byte cipher direction 1, 64 byte hmac direction 1 (=> 2048 bit)
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key = readkey(args.tls_auth)
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if key == None: return critical('cannot read tls auth file')
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index_start = HMAC_CLIENT_KEY_START * 2
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index_end = (HMAC_CLIENT_KEY_START + digest_size) * 2
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key = key[index_start:index_end]
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index_start = MAX_CIPHER_KEY_LENGTH + MAX_HMAC_KEY_LENGTH + MAX_CIPHER_KEY_LENGTH
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index_end = index_start + MAX_HMAC_KEY_LENGTH
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client_key = key[index_start:index_end]
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index_start = MAX_CIPHER_KEY_LENGTH
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index_end = index_start + MAX_HMAC_KEY_LENGTH
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server_key = key[index_start:index_end]
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if args.tls_auth_inverse: client_key, server_key = server_key, client_key
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# reduce key size to required size
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client_key = client_key[:digest_size]
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server_key = server_key[:digest_size]
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if key: key = binascii.unhexlify(key)
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return checkserver(args.host, args.port, args.tcp, args.timeout, key, digest)
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return check(args.host, args.port, args.tcp, args.timeout, digest, digest_size, client_key, server_key, args.retrycount, not args.no_validation)
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if __name__ == '__main__':
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code = main()
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