Added client audit functionality. (#3)

ssh-audit.py

@@ -28,6 +28,7 @@ from __future__ import print_function
 import binascii, os, io, sys, socket, struct, random, errno, getopt, re, hashlib, base64
 
 VERSION = 'v2.1.0-dev'
+SSH_HEADER = 'SSH-{0}-OpenSSH_8.0' # SSH software to impersonate
 
 if sys.version_info.major < 3:
         print("\n!!!! NOTE: Python 2 is being considered for deprecation.  If you have a good reason to need continued Python 2 support, please e-mail jtesta@positronsecurity.com with your rationale.\n\n")
@@ -69,6 +70,7 @@ def usage(err=None):
 	uout.info('   -6,  --ipv6             enable IPv6 (order of precedence)')
 	uout.info('   -p,  --port=<port>      port to connect')
 	uout.info('   -b,  --batch            batch output')
+	uout.info('   -c,  --client-audit     starts a server on port 2222 to audit client\n                               software config (use -p to change port)')
 	uout.info('   -n,  --no-colors        disable colors')
 	uout.info('   -v,  --verbose          verbose output')
 	uout.info('   -l,  --level=<level>    minimum output level (info|warn|fail)')
@@ -86,6 +88,7 @@ class AuditConf(object):
 		self.ssh1 = True
 		self.ssh2 = True
 		self.batch = False
+		self.client_audit = False
 		self.colors = True
 		self.verbose = False
 		self.level = 'info'
@@ -97,7 +100,7 @@ class AuditConf(object):
 	def __setattr__(self, name, value):
 		# type: (str, Union[str, int, bool, Sequence[int]]) -> None
 		valid = False
-		if name in ['ssh1', 'ssh2', 'batch', 'colors', 'verbose']:
+		if name in ['ssh1', 'ssh2', 'batch', 'client_audit', 'colors', 'verbose']:
 			valid, value = True, True if bool(value) else False
 		elif name in ['ipv4', 'ipv6']:
 			valid = False
@@ -144,9 +147,9 @@ class AuditConf(object):
 		# pylint: disable=too-many-branches
 		aconf = cls()
 		try:
-			sopts = 'h1246p:bnvl:t:'
+			sopts = 'h1246p:bcnvl:t:'
 			lopts = ['help', 'ssh1', 'ssh2', 'ipv4', 'ipv6', 'port',
-			         'batch', 'no-colors', 'verbose', 'level=', 'timeout=']
+			         'batch', 'client-audit', 'no-colors', 'verbose', 'level=', 'timeout=']
 			opts, args = getopt.getopt(args, sopts, lopts)
 		except getopt.GetoptError as err:
 			usage_cb(str(err))
@@ -168,6 +171,8 @@ class AuditConf(object):
 			elif o in ('-b', '--batch'):
 				aconf.batch = True
 				aconf.verbose = True
+			elif o in ('-c', '--client-audit'):
+				aconf.client_audit = True
 			elif o in ('-n', '--no-colors'):
 				aconf.colors = False
 			elif o in ('-v', '--verbose'):
@@ -178,8 +183,9 @@ class AuditConf(object):
 				aconf.level = a
 			elif o in ('-t', '--timeout'):
 				aconf.timeout = float(a)
-		if len(args) == 0:
+		if len(args) == 0 and aconf.client_audit == False:
 			usage_cb()
+		if aconf.client_audit == False:
 			if oport is not None:
 				host = args[0]
 			else:
@@ -192,9 +198,13 @@ class AuditConf(object):
 						host, oport = args[0], '22'
 					else:
 						host, oport = s[0], s[1] if len(s) > 1 else '22'
-		port = utils.parse_int(oport)
 			if not host:
 				usage_cb('host is empty')
+		else:
+			host = None
+			if oport is None:
+				oport = '2222'
+		port = utils.parse_int(oport)
 		if port <= 0 or port > 65535:
 			usage_cb('port {0} is not valid'.format(oport))
 		aconf.host = host
@@ -343,6 +353,7 @@ class SSH2(object):  # pylint: disable=too-few-public-methods
 				'rsa1024-sha1': [[], [], [WARN_MODULUS_SIZE, WARN_HASH_WEAK]],
 				'rsa2048-sha256': [[]],
                                 'sntrup4591761x25519-sha512@tinyssh.org': [['8.0'], [], [WARN_EXPERIMENTAL]],
+                                'ext-info-c': [[]], # Extension negotiation (RFC 8308)
 			},
 			'key': {
 				'rsa-sha2-256': [['7.2']],
@@ -1217,6 +1228,7 @@ class SSH(object):  # pylint: disable=too-few-public-methods
 		DropbearSSH = 'Dropbear SSH'
 		LibSSH = 'libssh'
 		TinySSH = 'TinySSH'
+		PuTTY = 'PuTTY'
 	
 	class Software(object):
 		def __init__(self, vendor, product, version, patch, os_version):
@@ -1420,6 +1432,9 @@ class SSH(object):  # pylint: disable=too-few-public-methods
 			mx = re.match(r'^tinyssh_(.*)', software)
 			if bool(mx):
 				return cls(None, SSH.Product.TinySSH, mx.group(1), None, None)
+			mx = re.match(r'^PuTTY_Release_(.*)', software)
+			if bool(mx):
+				return cls(None, SSH.Product.PuTTY, mx.group(1), None, None)
 			return None
 	
 	class Banner(object):
@@ -1910,7 +1925,19 @@ class SSH(object):  # pylint: disable=too-few-public-methods
 				['3.0',     '3.0p1',   1, 'CVE-2001-1507',  7.5, 'bypass authentication'],
 				['1.2.3',   '3.0.1p1', 5, 'CVE-2001-0872',  7.2, 'privilege escalation via crafted environment variables'],
 				['1.2.3',   '2.1.1',   1, 'CVE-2001-0361',  4.0, 'recover plaintext from ciphertext'],
-				['1.2',     '2.1',     1, 'CVE-2000-0525', 10.0, 'execute arbitrary code (improper privileges)']]
+				['1.2',     '2.1',     1, 'CVE-2000-0525', 10.0, 'execute arbitrary code (improper privileges)']],
+			'PuTTY': [
+				['0.0', '0.71', 2, 'CVE-2019-XXXX', 5.0, 'undefined vulnerability in obsolete SSHv1 protocol handling'],
+				['0.0', '0.71', 6, 'CVE-2019-XXXX', 5.0, 'local privilege escalation in Pageant'],
+				['0.0', '0.70', 2, 'CVE-2019-9898', 7.5, 'potential recycling of random numbers'],
+				['0.0', '0.70', 2, 'CVE-2019-9897', 5.0, 'multiple denial-of-service issues from writing to the terminal'],
+				['0.0', '0.70', 6, 'CVE-2019-9896', 4.6, 'local application hijacking through malicious Windows help file'],
+				['0.0', '0.70', 2, 'CVE-2019-9894', 6.4, 'buffer overflow in RSA key exchange'],
+				['0.0', '0.69', 6, 'CVE-2016-6167', 4.4, 'local application hijacking through untrusted DLL loading'],
+				['0.0', '0.67', 2, 'CVE-2017-6542', 7.5, 'buffer overflow in UNIX client that can result in privilege escalation or denial-of-service'],
+				['0.0', '0.66', 2, 'CVE-2016-2563', 7.5, 'buffer overflow in SCP command-line utility'],
+				['0.0', '0.65', 2, 'CVE-2015-5309', 4.3, 'integer overflow in terminal-handling code'],
+			]
 		}  # type: Dict[str, List[List[Any]]]
 		TXT = {
 			'Dropbear SSH': [
@@ -1931,12 +1958,13 @@ class SSH(object):  # pylint: disable=too-few-public-methods
 			# type: (Optional[str], int) -> None
 			super(SSH.Socket, self).__init__()
 			self.__sock = None  # type: Optional[socket.socket]
+			self.__sock_server = None
 			self.__block_size = 8
 			self.__state = 0
 			self.__header = []  # type: List[text_type]
 			self.__banner = None  # type: Optional[SSH.Banner]
-			if host is None:
+#			if host is None:
-				raise ValueError('undefined host')
+#				raise ValueError('undefined host')
 			nport = utils.parse_int(port)
 			if nport < 1 or nport > 65535:
 				raise ValueError('invalid port: {0}'.format(port))
@@ -1972,6 +2000,25 @@ class SSH(object):  # pylint: disable=too-few-public-methods
 				out.fail('[exception] {0}'.format(e))
 				sys.exit(1)
 
+
+		# Listens on a server socket and accepts one connection (used for
+		# auditing client connections).
+		def listen_and_accept(self):
+			s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+			s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+			self.__sock_server = s
+
+			# TODO: listen on IPv6 address if necessary.
+			s.bind(('0.0.0.0', self.__port))
+			s.listen()
+
+			c, addr = s.accept()
+			self.client_host = addr[0]
+			self.client_port = addr[1]
+			c.settimeout(self.__timeout)
+			self.__sock = c
+
+
 		def connect(self):
 			# type: () -> None
 			err = None
@@ -1998,15 +2045,15 @@ class SSH(object):  # pylint: disable=too-few-public-methods
 			# type: (int) -> Tuple[Optional[SSH.Banner], List[text_type], Optional[str]]
 			if self.__sock is None:
 				return self.__banner, self.__header, 'not connected'
-			banner = 'SSH-{0}-OpenSSH_7.4'.format('1.5' if sshv == 1 else '2.0')
+			banner = SSH_HEADER.format('1.5' if sshv == 1 else '2.0')
-			rto = self.__sock.gettimeout()
-			self.__sock.settimeout(0.7)
-			s, e = self.recv()
-			self.__sock.settimeout(rto)
-			if s < 0:
-				return self.__banner, self.__header, e
 			if self.__state < self.SM_BANNER_SENT:
 				self.send_banner(banner)
+#			rto = self.__sock.gettimeout()
+#			self.__sock.settimeout(0.7)
+			s, e = self.recv()
+#			self.__sock.settimeout(rto)
+			if s < 0:
+				return self.__banner, self.__header, e
 			e = None
 			while self.__banner is None:
 				if not s > 0:
@@ -2163,6 +2210,7 @@ class SSH(object):  # pylint: disable=too-few-public-methods
 		def __cleanup(self):
 			# type: () -> None
 			self._close_socket(self.__sock)
+			self._close_socket(self.__sock_server)
 			self.__sock = None
 
 
@@ -2643,8 +2691,13 @@ def output_algorithm(alg_db, alg_type, alg_name, unknown_algs, alg_max_len=0, al
 				f(' ' * len(prefix + alg_name) + comment)
 
 
-def output_compatibility(algs, for_server=True):
+def output_compatibility(algs, client_audit, for_server=True):
 	# type: (SSH.Algorithms, bool) -> None
+
+	# Don't output any compatibility info if we're doing a client audit.
+	if client_audit:
+		return
+
 	ssh_timeframe = algs.get_ssh_timeframe(for_server)
 	comp_text = []
 	for ssh_prod in [SSH.Product.OpenSSH, SSH.Product.DropbearSSH]:
@@ -2669,7 +2722,7 @@ def output_compatibility(algs, for_server=True):
 		out.good('(gen) compatibility: ' + ', '.join(comp_text))
 
 
-def output_security_sub(sub, software, padlen):
+def output_security_sub(sub, software, client_audit, padlen):
 	# type: (str, Optional[SSH.Software], int) -> None
 	secdb = SSH.Security.CVE if sub == 'cve' else SSH.Security.TXT
 	if software is None or software.product not in secdb:
@@ -2680,9 +2733,11 @@ def output_security_sub(sub, software, padlen):
 			continue
 		target, name = line[2:4]  # type: int, str
 		is_server = target & 1 == 1
-		# is_client = target & 2 == 2
+		is_client = target & 2 == 2
 		# is_local = target & 4 == 4
-		if not is_server:
+
+		# If this security entry applies only to servers, but we're testing a client, then skip it.  Similarly, skip entries that apply only to clients, but we're testing a server.
+		if (is_server and not is_client and client_audit) or (is_client and not is_server and not client_audit):
 			continue
 		p = '' if out.batch else ' ' * (padlen - len(name))
 		if sub == 'cve':
@@ -2698,13 +2753,13 @@ def output_security_sub(sub, software, padlen):
 			out.fail('(sec) {0}{1} -- {2}'.format(name, p, descr))
 
 
-def output_security(banner, padlen):
+def output_security(banner, client_audit, padlen):
 	# type: (Optional[SSH.Banner], int) -> None
 	with OutputBuffer() as obuf:
 		if banner is not None:
 			software = SSH.Software.parse(banner)
-			output_security_sub('cve', software, padlen)
+			output_security_sub('cve', software, client_audit, padlen)
-			output_security_sub('txt', software, padlen)
+			output_security_sub('txt', software, client_audit, padlen)
 	if len(obuf) > 0:
 		out.head('# security')
 		obuf.flush()
@@ -2749,8 +2804,39 @@ def output_fingerprints(algs, sha256=True):
 		out.sep()
 
 
+# Returns True if no warnings or failures encountered in configuration.
 def output_recommendations(algs, software, padlen=0):
 	# type: (SSH.Algorithms, Optional[SSH.Software], int) -> None
+
+	ret = True
+	# PuTTY's algorithms cannot be modified, so there's no point in issuing recommendations.
+	if software.product == SSH.Product.PuTTY:
+		max_vuln_version = 0.0
+		max_cvssv2_severity = 0.0
+		# Search the CVE database for the most recent vulnerable version and the max CVSSv2 score.
+		for cve_list in SSH.Security.CVE['PuTTY']:
+			vuln_version = float(cve_list[1])
+			cvssv2_severity = cve_list[4]
+
+			if vuln_version > max_vuln_version:
+				max_vuln_version = vuln_version
+			if cvssv2_severity > max_cvssv2_severity:
+				max_cvssv2_severity = cvssv2_severity
+
+		fn = out.warn
+		if max_cvssv2_severity > 8.0:
+			fn = out.fail
+
+		# Assuming that PuTTY versions will always increment by 0.01, we can calculate the first safe version by adding 0.01 to the latest vulnerable version.
+		current_version = float(software.version)
+		upgrade_to_version = max_vuln_version + 0.01
+		if current_version < upgrade_to_version:
+			out.head('# recommendations')
+			fn('(rec) Upgrade to PuTTY v%.2f' % upgrade_to_version)
+			out.sep()
+			ret = False
+		return ret
+
 	for_server = True
 	with OutputBuffer() as obuf:
 		software, alg_rec = algs.get_recommendations(software, for_server)
@@ -2768,12 +2854,14 @@ def output_recommendations(algs, software, padlen=0):
 						chg_additional_info = ''
 						if action == 'del':
 							an, sg, fn = 'remove', '-', out.warn
+							ret = False
 							if alg_rec[sshv][alg_type][action][name] >= 10:
 								fn = out.fail
 						elif action == 'add':
 							an, sg, fn = 'append', '+', out.good
 						elif action == 'chg':
 							an, sg, fn = 'change', '!', out.fail
+							ret = False
 							chg_additional_info = ' (increase modulus size to 2048 bits or larger)'
 						b = '(SSH{0})'.format(sshv) if sshv == 1 else ''
 						fm = '(rec) {0}{1}{2}-- {3} algorithm to {4}{5} {6}'
@@ -2786,9 +2874,27 @@ def output_recommendations(algs, software, padlen=0):
 		out.head('# algorithm recommendations {0}'.format(title))
 		obuf.flush(True) # Sort the output so that it is always stable (needed for repeatable testing).
 		out.sep()
+	return ret
 
 
-def output(banner, header, kex=None, pkm=None):
+# Output additional information & notes.
+def output_info(algs, software, client_audit, any_problems, padlen=0):
+	with OutputBuffer() as obuf:
+		# Tell user that PuTTY cannot be hardened at the protocol-level.
+		if client_audit and (software.product == SSH.Product.PuTTY):
+			out.warn('(nfo) PuTTY does not have the option of restricting any algorithms during the SSH handshake.')
+
+		# If any warnings or failures were given, print a link to the hardening guides.
+		if any_problems:
+			out.warn('(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>')
+
+	if len(obuf) > 0:
+		out.head('# additional info')
+		obuf.flush()
+		out.sep()
+
+
+def output(banner, header, client_audit=False, kex=None, pkm=None):
 	# type: (Optional[SSH.Banner], List[text_type], Optional[SSH2.Kex], Optional[SSH1.PublicKeyMessage]) -> None
 	sshv = 1 if pkm is not None else 2
 	algs = SSH.Algorithms(pkm, kex)
@@ -2807,7 +2913,7 @@ def output(banner, header, kex=None, pkm=None):
 				out.good('(gen) software: {0}'.format(software))
 		else:
 			software = None
-		output_compatibility(algs)
+		output_compatibility(algs, client_audit)
 		if kex is not None:
 			compressions = [x for x in kex.server.compression if x != 'none']
 			if len(compressions) > 0:
@@ -2820,7 +2926,7 @@ def output(banner, header, kex=None, pkm=None):
 		obuf.flush()
 		out.sep()
 	maxlen = algs.maxlen + 1
-	output_security(banner, maxlen)
+	output_security(banner, client_audit, maxlen)
 	unknown_algorithms = []  # Filled in by output_algorithms() with unidentified algs.
 	if pkm is not None:
 		adb = SSH1.KexDB.ALGORITHMS
@@ -2843,7 +2949,9 @@ def output(banner, header, kex=None, pkm=None):
 		title, atype = 'message authentication code algorithms', 'mac'
 		output_algorithms(title, adb, atype, kex.server.mac, unknown_algorithms, maxlen)
 	output_fingerprints(algs, True)
-	output_recommendations(algs, software, maxlen)
+	perfect_config = output_recommendations(algs, software, maxlen)
+	output_info(algs, software, client_audit, not perfect_config)
+
 
 	# If we encountered any unknown algorithms, ask the user to report them.
 	if len(unknown_algorithms) > 0:
@@ -2979,6 +3087,9 @@ def audit(aconf, sshv=None):
 	out.level = aconf.level
 	out.use_colors = aconf.colors
 	s = SSH.Socket(aconf.host, aconf.port, aconf.ipvo, aconf.timeout)
+	if aconf.client_audit:
+		s.listen_and_accept()
+	else:
 		s.connect()
 	if sshv is None:
 		sshv = 2 if aconf.ssh2 else 1
@@ -3023,9 +3134,10 @@ def audit(aconf, sshv=None):
 		output(banner, header, pkm=pkm)
 	elif sshv == 2:
 		kex = SSH2.Kex.parse(payload)
+		if aconf.client_audit is False:
 			SSH2.HostKeyTest.run(s, kex)
 			SSH2.GEXTest.run(s, kex)
-		output(banner, header, kex=kex)
+		output(banner, header, client_audit=aconf.client_audit, kex=kex)
 
 
 utils = Utils()

test/docker/expected_results/dropbear_2019.78_test1.txt

@@ -80,3 +80,6 @@
 (rec) -diffie-hellman-group14-sha1   -- kex algorithm to remove 
 (rec) -hmac-sha1                     -- mac algorithm to remove 
 
+# additional info
+(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>
+

test/docker/expected_results/openssh_4.0p1_test1.txt

@@ -134,3 +134,6 @@
 (rec) -rijndael-cbc@lysator.liu.se        -- enc algorithm to remove 
 (rec) -ssh-dss                            -- key algorithm to remove 
 
+# additional info
+(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>
+

test/docker/expected_results/openssh_5.6p1_test1.txt

@@ -143,3 +143,6 @@
 (rec) -ssh-dss                              -- key algorithm to remove 
 (rec) -diffie-hellman-group14-sha1          -- kex algorithm to remove 
 
+# additional info
+(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>
+

test/docker/expected_results/openssh_5.6p1_test2.txt

@@ -141,3 +141,6 @@
 (rec) -rijndael-cbc@lysator.liu.se          -- enc algorithm to remove 
 (rec) -diffie-hellman-group14-sha1          -- kex algorithm to remove 
 
+# additional info
+(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>
+

test/docker/expected_results/openssh_5.6p1_test3.txt

@@ -141,3 +141,6 @@
 (rec) -rijndael-cbc@lysator.liu.se          -- enc algorithm to remove 
 (rec) -diffie-hellman-group14-sha1          -- kex algorithm to remove 
 
+# additional info
+(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>
+

test/docker/expected_results/openssh_5.6p1_test4.txt

@@ -139,3 +139,6 @@
 (rec) -rijndael-cbc@lysator.liu.se          -- enc algorithm to remove 
 (rec) -diffie-hellman-group14-sha1          -- kex algorithm to remove 
 
+# additional info
+(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>
+

test/docker/expected_results/openssh_5.6p1_test5.txt

@@ -137,3 +137,6 @@
 (rec) -rijndael-cbc@lysator.liu.se          -- enc algorithm to remove 
 (rec) -diffie-hellman-group14-sha1          -- kex algorithm to remove 
 
+# additional info
+(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>
+

test/docker/expected_results/openssh_8.0p1_test1.txt

@@ -77,3 +77,6 @@
 (rec) -umac-64-etm@openssh.com              -- mac algorithm to remove 
 (rec) -umac-64@openssh.com                  -- mac algorithm to remove 
 
+# additional info
+(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>
+

test/docker/expected_results/openssh_8.0p1_test2.txt

@@ -73,3 +73,6 @@
 (rec) -umac-64-etm@openssh.com              -- mac algorithm to remove 
 (rec) -umac-64@openssh.com                  -- mac algorithm to remove 
 
+# additional info
+(nfo) For hardening guides on common OSes, please see: <https://www.ssh-audit.com/hardening_guides.html>
+