mirror of
https://github.com/jtesta/ssh-audit.git
synced 2024-11-22 10:31:41 +01:00
DH GEX Modulus Size Testing
This commit is contained in:
Adam Russell
Joe Testa
parent
0a6ac5de54
commit
5ac0ffa8f1
@ -59,6 +59,7 @@ class AuditConf:
|
||||
self.lookup = ''
|
||||
self.manual = False
|
||||
self.debug = False
|
||||
self.gex_test = ''
|
||||
|
||||
def __setattr__(self, name: str, value: Union[str, int, float, bool, Sequence[int]]) -> None:
|
||||
valid = False
|
||||
@ -86,7 +87,7 @@ class AuditConf:
|
||||
if value == -1.0:
|
||||
raise ValueError('invalid timeout: {}'.format(value))
|
||||
valid = True
|
||||
elif name in ['ip_version_preference', 'lookup', 'policy_file', 'policy', 'target_file', 'target_list']:
|
||||
elif name in ['ip_version_preference', 'lookup', 'policy_file', 'policy', 'target_file', 'target_list', 'gex_test']:
|
||||
valid = True
|
||||
elif name == "threads":
|
||||
valid, num_threads = True, Utils.parse_int(value)
|
||||
|
||||
@ -33,6 +33,7 @@ from ssh_audit.ssh2_kexdb import SSH2_KexDB
|
||||
from ssh_audit.ssh2_kex import SSH2_Kex
|
||||
from ssh_audit.ssh_socket import SSH_Socket
|
||||
from ssh_audit.outputbuffer import OutputBuffer
|
||||
from ssh_audit import exitcodes
|
||||
|
||||
|
||||
# Performs DH group exchanges to find what moduli are supported, and checks
|
||||
@ -70,6 +71,76 @@ class GEXTest:
|
||||
|
||||
return True
|
||||
|
||||
# Tests for modulus size in bits against the specified target.
|
||||
@staticmethod
|
||||
def modulus_size_test(out: 'OutputBuffer', s: 'SSH_Socket', kex: 'SSH2_Kex', bits_min: int, bits_pref: int, bits_max: int, modulus_dict: Dict[str, List[int]]) -> int:
|
||||
'''
|
||||
Tests for modulus size in bits against the target target.
|
||||
Builds a dictionary, where a key represents a DH algorithm name and the
|
||||
values are the modulus sizes (in bits) that have been returned by the
|
||||
target server.
|
||||
Returns an exitcodes.* flag.
|
||||
'''
|
||||
|
||||
retval = exitcodes.GOOD
|
||||
|
||||
out.d("Starting modulus_size_test...")
|
||||
out.d("Bits Min: " + str(bits_min))
|
||||
out.d("Bits Pref: " + str(bits_pref))
|
||||
out.d("Bits Max: " + str(bits_max))
|
||||
|
||||
if all(x < 0 for x in (bits_min, bits_pref, bits_max)):
|
||||
out.fail("min, pref and max values cannot be negative.")
|
||||
return exitcodes.FAILURE
|
||||
|
||||
GEX_ALGS = {
|
||||
'diffie-hellman-group-exchange-sha1': KexGroupExchange_SHA1,
|
||||
'diffie-hellman-group-exchange-sha256': KexGroupExchange_SHA256,
|
||||
}
|
||||
|
||||
# Check if the server supports any of the group-exchange
|
||||
# algorithms. If so, test each one.
|
||||
for gex_alg in GEX_ALGS:
|
||||
if gex_alg not in kex.kex_algorithms:
|
||||
out.d('Server does not support the algorithm "' + gex_alg + '".', write_now=True)
|
||||
else:
|
||||
kex_group = GEX_ALGS[gex_alg]()
|
||||
out.d('Preparing to perform DH group exchange using ' + gex_alg + ' with min, pref and max modulus sizes of ' + str(bits_min) + ' bits, ' + str(bits_pref) + ' bits and ' + str(bits_max) + ' bits...', write_now=True)
|
||||
|
||||
# It has been observed that reconnecting to some SSH servers
|
||||
# multiple times in quick succession can eventually result
|
||||
# in a "connection reset by peer" error. It may be possible
|
||||
# to recover from such an error by sleeping for some time
|
||||
# before continuing to issue reconnects.
|
||||
if GEXTest.reconnect(out, s, kex, gex_alg) is False:
|
||||
out.fail('Reconnect failed.')
|
||||
return exitcodes.FAILURE
|
||||
try:
|
||||
modulus_size_returned = None
|
||||
kex_group.send_init_gex(s, bits_min, bits_pref, bits_max)
|
||||
kex_group.recv_reply(s, False)
|
||||
modulus_size_returned = kex_group.get_dh_modulus_size()
|
||||
out.d('Modulus size returned by server: ' + str(modulus_size_returned) + ' bits', write_now=True)
|
||||
except Exception as e:
|
||||
out.d('[exception] ' + str(e), write_now=True)
|
||||
# import traceback
|
||||
# print(traceback.format_exc())
|
||||
pass
|
||||
finally:
|
||||
# The server is in a state that is not re-testable,
|
||||
# so there's nothing else to do with this open
|
||||
# connection.
|
||||
s.close()
|
||||
|
||||
if modulus_size_returned is not None:
|
||||
if gex_alg in modulus_dict:
|
||||
if modulus_size_returned not in modulus_dict[gex_alg]:
|
||||
modulus_dict[gex_alg].append(modulus_size_returned)
|
||||
else:
|
||||
modulus_dict[gex_alg] = [modulus_size_returned]
|
||||
|
||||
return retval
|
||||
|
||||
# Runs the DH moduli test against the specified target.
|
||||
@staticmethod
|
||||
def run(out: 'OutputBuffer', s: 'SSH_Socket', kex: 'SSH2_Kex') -> None:
|
||||
@ -88,7 +159,8 @@ class GEXTest:
|
||||
# algorithms. If so, test each one.
|
||||
for gex_alg, kex_group_class in GEX_ALGS.items():
|
||||
if gex_alg in kex.kex_algorithms:
|
||||
out.d('Preparing to perform DH group exchange using ' + gex_alg + '...', write_now=True)
|
||||
weak_sizes = 512, 1024, 1536
|
||||
out.d('Preparing to perform DH group exchange using ' + gex_alg + ' with min, pref and max modulus sizes of ' + str(weak_sizes[0]) + ' bits, ' + str(weak_sizes[1]) + ' bits and ' + str(weak_sizes[2]) + ' bits...', write_now=True)
|
||||
|
||||
if GEXTest.reconnect(out, s, kex, gex_alg) is False:
|
||||
break
|
||||
@ -98,15 +170,17 @@ class GEXTest:
|
||||
|
||||
# First try a range of weak sizes.
|
||||
try:
|
||||
kex_group.send_init_gex(s, 512, 1024, 1536)
|
||||
kex_group.send_init_gex(s, weak_sizes[0], weak_sizes[1], weak_sizes[2])
|
||||
kex_group.recv_reply(s, False)
|
||||
|
||||
# Its been observed that servers will return a group
|
||||
# larger than the requested max. So just because we
|
||||
# got here, doesn't mean the server is vulnerable...
|
||||
smallest_modulus = kex_group.get_dh_modulus_size()
|
||||
out.d('Modulus size returned by server: ' + str(smallest_modulus) + ' bits', write_now=True)
|
||||
|
||||
except Exception:
|
||||
except Exception as e:
|
||||
out.d('[exception] ' + str(e), write_now=True)
|
||||
pass
|
||||
finally:
|
||||
s.close()
|
||||
@ -120,7 +194,7 @@ class GEXTest:
|
||||
if bits >= smallest_modulus > 0:
|
||||
break
|
||||
|
||||
out.d('Preparing to perform DH group exchange using ' + gex_alg + ' with modulus size ' + str(bits) + '...', write_now=True)
|
||||
out.d('Preparing to perform DH group exchange using ' + gex_alg + ' with min, pref and max modulus sizes of ' + str(bits) + ' bits...', write_now=True)
|
||||
|
||||
if GEXTest.reconnect(out, s, kex, gex_alg) is False:
|
||||
reconnect_failed = True
|
||||
@ -130,7 +204,9 @@ class GEXTest:
|
||||
kex_group.send_init_gex(s, bits, bits, bits)
|
||||
kex_group.recv_reply(s, False)
|
||||
smallest_modulus = kex_group.get_dh_modulus_size()
|
||||
except Exception:
|
||||
out.d('Modulus size returned by server: ' + str(smallest_modulus) + ' bits', write_now=True)
|
||||
except Exception as e:
|
||||
out.d('[exception] ' + str(e), write_now=True)
|
||||
# import traceback
|
||||
# print(traceback.format_exc())
|
||||
pass
|
||||
|
||||
@ -87,6 +87,7 @@ def usage(err: Optional[str] = None) -> None:
|
||||
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;\n use -t to change timeout)')
|
||||
uout.info(' -d, --debug debug output')
|
||||
uout.info(' -g, --gex-test=<n[,n,...] | min:pref:max[,min:pref:max,...] | n-n[:step]> dh gex modulus size test')
|
||||
uout.info(' -j, --json JSON output (use -jj to enable indents)')
|
||||
uout.info(' -l, --level=<level> minimum output level (info|warn|fail)')
|
||||
uout.info(' -L, --list-policies list all the official, built-in policies')
|
||||
@ -589,8 +590,8 @@ def process_commandline(out: OutputBuffer, args: List[str], usage_cb: Callable[.
|
||||
# pylint: disable=too-many-branches
|
||||
aconf = AuditConf()
|
||||
try:
|
||||
sopts = 'h1246M:p:P:jbcnvl:t:T:Lmd'
|
||||
lopts = ['help', 'ssh1', 'ssh2', 'ipv4', 'ipv6', 'make-policy=', 'port=', 'policy=', 'json', 'batch', 'client-audit', 'no-colors', 'verbose', 'level=', 'timeout=', 'targets=', 'list-policies', 'lookup=', 'threads=', 'manual', 'debug']
|
||||
sopts = 'h1246M:p:P:jbcnvl:t:T:Lmdg:'
|
||||
lopts = ['help', 'ssh1', 'ssh2', 'ipv4', 'ipv6', 'make-policy=', 'port=', 'policy=', 'json', 'batch', 'client-audit', 'no-colors', 'verbose', 'level=', 'timeout=', 'targets=', 'list-policies', 'lookup=', 'threads=', 'manual', 'debug', 'gex-test=']
|
||||
opts, args = getopt.gnu_getopt(args, sopts, lopts)
|
||||
except getopt.GetoptError as err:
|
||||
usage_cb(str(err))
|
||||
@ -652,6 +653,10 @@ def process_commandline(out: OutputBuffer, args: List[str], usage_cb: Callable[.
|
||||
elif o in ('-d', '--debug'):
|
||||
aconf.debug = True
|
||||
out.debug = True
|
||||
elif o in ('-g', '--gex-test'):
|
||||
if not((any(re.search(regex_str, a) for regex_str in get_permitted_syntax_for_gex_test().values()))):
|
||||
usage_cb('{} {} is not valid'.format(o, a))
|
||||
aconf.gex_test = a
|
||||
|
||||
if len(args) == 0 and aconf.client_audit is False and aconf.target_file is None and aconf.list_policies is False and aconf.lookup == '' and aconf.manual is False:
|
||||
usage_cb()
|
||||
@ -922,6 +927,10 @@ def audit(out: OutputBuffer, aconf: AuditConf, sshv: Optional[int] = None, print
|
||||
|
||||
if aconf.client_audit is False:
|
||||
HostKeyTest.run(out, s, kex)
|
||||
if aconf.gex_test != '':
|
||||
program_retval = invoke_modulus_size_test(out, s, kex, aconf)
|
||||
return program_retval
|
||||
else:
|
||||
GEXTest.run(out, s, kex)
|
||||
|
||||
# This is a standard audit scan.
|
||||
@ -1061,6 +1070,91 @@ def windows_manual(out: OutputBuffer) -> int:
|
||||
return retval
|
||||
|
||||
|
||||
def get_permitted_syntax_for_gex_test() -> Dict[str, str]:
|
||||
syntax = {
|
||||
'RANGE': r'^\d+-\d+(:\d+)?$',
|
||||
'LIST_WITHOUT_MIN_PREF_MAX': r'^\d+(,\d+)*$',
|
||||
'LIST_WITH_MIN_PREF_MAX': r'^\d+:\d+:\d+(,\d+:\d+:\d+)*$'
|
||||
}
|
||||
return syntax
|
||||
|
||||
|
||||
def invoke_modulus_size_test(out: OutputBuffer, s: 'SSH_Socket', kex: 'SSH2_Kex', aconf: AuditConf) -> int:
|
||||
'''Extracts the user specified modulus sizes and submits them for testing against the target target. Returns an exitcodes.* flag.'''
|
||||
|
||||
permitted_syntax = get_permitted_syntax_for_gex_test()
|
||||
|
||||
if not((any(re.search(regex_str, aconf.gex_test) for regex_str in permitted_syntax.values()))):
|
||||
out.fail("Invalid syntax.")
|
||||
return exitcodes.FAILURE
|
||||
|
||||
mod_dict: Dict[str, List[int]] = {}
|
||||
|
||||
# Range syntax.
|
||||
if re.search(permitted_syntax['RANGE'], aconf.gex_test):
|
||||
extracted_digits = re.findall(r'\d+', aconf.gex_test)
|
||||
bits_left_bound = int(extracted_digits[0])
|
||||
bits_right_bound = int(extracted_digits[1])
|
||||
|
||||
if (len(extracted_digits)) == 3:
|
||||
bits_step = int(extracted_digits[2])
|
||||
else:
|
||||
bits_step = 1
|
||||
|
||||
if bits_step <= 0:
|
||||
out.fail("Step value must be greater than zero.")
|
||||
return exitcodes.FAILURE
|
||||
|
||||
if all(x < 0 for x in (bits_left_bound, bits_right_bound)):
|
||||
out.fail("Start and end values cannot be negative.")
|
||||
return exitcodes.FAILURE
|
||||
|
||||
# If the left value is greater than the right value, then the sequence
|
||||
# operates from right to left.
|
||||
if bits_left_bound <= bits_right_bound:
|
||||
bits_in_range_to_test = range(bits_left_bound, bits_right_bound + 1, bits_step)
|
||||
else:
|
||||
bits_in_range_to_test = range(bits_left_bound, bits_right_bound - 1, -abs(bits_step))
|
||||
|
||||
out.v("A separate test will be performed against each of the following modulus sizes: " + ", ".join([str(x) for x in bits_in_range_to_test]) + ".", write_now=True)
|
||||
|
||||
for i_bits in bits_in_range_to_test:
|
||||
program_retval = GEXTest.modulus_size_test(out, s, kex, i_bits, i_bits, i_bits, mod_dict)
|
||||
if program_retval != exitcodes.GOOD:
|
||||
return program_retval
|
||||
|
||||
# Two variations of list syntax.
|
||||
if re.search(permitted_syntax['LIST_WITHOUT_MIN_PREF_MAX'], aconf.gex_test):
|
||||
bits_in_list_to_test = aconf.gex_test.split(',')
|
||||
out.v("A separate test will be performed against each of the following modulus sizes: " + ", ".join([str(x) for x in bits_in_list_to_test]) + ".", write_now=True)
|
||||
for s_bits in bits_in_list_to_test:
|
||||
program_retval = GEXTest.modulus_size_test(out, s, kex, int(s_bits), int(s_bits), int(s_bits), mod_dict)
|
||||
if program_retval != exitcodes.GOOD:
|
||||
return program_retval
|
||||
if re.search(permitted_syntax['LIST_WITH_MIN_PREF_MAX'], aconf.gex_test):
|
||||
sets_of_min_pref_max = aconf.gex_test.split(',')
|
||||
out.v("A separate test will be performed against each of the following sets of 'min:pref:max' modulus sizes: " + ', '.join(sets_of_min_pref_max), write_now=True)
|
||||
for set_of_min_pref_max in sets_of_min_pref_max:
|
||||
bits_in_list_to_test = set_of_min_pref_max.split(':')
|
||||
program_retval = GEXTest.modulus_size_test(out, s, kex, int(bits_in_list_to_test[0]), int(bits_in_list_to_test[1]), int(bits_in_list_to_test[2]), mod_dict)
|
||||
if program_retval != exitcodes.GOOD:
|
||||
return program_retval
|
||||
|
||||
if mod_dict:
|
||||
if aconf.json:
|
||||
json_struct = {'dh-gex-modulus-size': mod_dict}
|
||||
out.info(json.dumps(json_struct, indent=4 if aconf.json_print_indent else None, sort_keys=True))
|
||||
else:
|
||||
out.head('# diffie-hellman group exchange modulus size')
|
||||
max_key_len = len(max(mod_dict, key=len))
|
||||
|
||||
for key, value in mod_dict.items():
|
||||
padding = (max_key_len - len(key)) + 1
|
||||
out.info(key + " " * padding + '--> ' + ', '.join(map(str, value)))
|
||||
|
||||
return program_retval
|
||||
|
||||
|
||||
def main() -> int:
|
||||
out = OutputBuffer()
|
||||
aconf = process_commandline(out, sys.argv[1:], usage)
|
||||
|
||||
65
ssh-audit.1
65
ssh-audit.1
@ -1,4 +1,4 @@
|
||||
.TH SSH-AUDIT 1 "March 2, 2021"
|
||||
.TH SSH-AUDIT 1 "February 13, 2022"
|
||||
.SH NAME
|
||||
\fBssh-audit\fP \- SSH server & client configuration auditor
|
||||
.SH SYNOPSIS
|
||||
@ -51,6 +51,43 @@ Starts a server on port 2222 to audit client software configuration. Use -p/--p
|
||||
.br
|
||||
Enable debug output.
|
||||
|
||||
.TP
|
||||
.B -g, \-\-gex-test=<n[,n,...] | min:pref:max[,min:pref:max,...] | n-n[:step]>
|
||||
.br
|
||||
Runs a Diffie-Hellman Group Exchange modulus size test against a server.
|
||||
|
||||
Diffie-Hellman requires the client and server to agree on a generator value and
|
||||
a modulus value. In the "Group Exchange" implementation of Diffie-Hellman, the
|
||||
client specifies the size of the modulus in bits by providing the server with
|
||||
minimum, preferred and maximum values. The server then finds a group that best
|
||||
matches the client's request, returning the corresponding generator and modulus.
|
||||
For a full explanation of this process see RFC 4419 and its successors.
|
||||
|
||||
This test acts as a client by providing an SSH server with the size of a modulus
|
||||
and then obtains the size of the modulus returned by the server.
|
||||
|
||||
Three types of syntax are supported:
|
||||
|
||||
1. <n[,n,...]>
|
||||
|
||||
A comma delimited list of modulus sizes.
|
||||
A test is performed against each value in the list where it acts as the minimum, preferred and maximum modulus size.
|
||||
|
||||
|
||||
2. <min:pref:max[,min:pref:max,...]>
|
||||
|
||||
A set of three colon delimited values denoting minimum, preferred and maximum modulus size.
|
||||
A test is performed against each set.
|
||||
Multiple sets can specified as a comma separated list.
|
||||
|
||||
3. <n-n[:step]>
|
||||
|
||||
A range of modulus sizes with an optional step value. Step defaults to 1 if omitted.
|
||||
If the left value is greater than the right value, then the sequence operates from right to left.
|
||||
A test is performed against each value in the range where it acts as the minimum, preferred and maximum modulus size.
|
||||
|
||||
Duplicates are excluded from the return value.
|
||||
|
||||
.TP
|
||||
.B -j, \-\-json
|
||||
.br
|
||||
@ -130,7 +167,7 @@ When the -P/--policy option is used, \fBssh-audit\fP performs a policy audit. T
|
||||
Policy auditing is helpful for ensuring a group of related servers are properly hardened to an exact specification.
|
||||
|
||||
.PP
|
||||
The set of official built-in policies can be viewed with -L/--list-policies. Multiple servers can be audited with -T/--targets=<servers.txt>. Custom policies can be made from an ideal target server with -M/--make-policy=<custom_policy.txt>.
|
||||
The set of official built-in policies can be viewed with -L/--list-policies. Multiple servers can be audited with -T/--targets=<servers.txt>. Custom policies can be made from an preferred target server with -M/--make-policy=<custom_policy.txt>.
|
||||
|
||||
|
||||
.SH EXAMPLES
|
||||
@ -219,6 +256,30 @@ ssh-audit -M new_policy.txt targetserver
|
||||
.fi
|
||||
.RE
|
||||
|
||||
.LP
|
||||
To run a Diffie-Hellman Group Exchange modulus size test using the values 2000 bits, 3000 bits, 4000 bits and 5000 bits:
|
||||
.RS
|
||||
.nf
|
||||
ssh-audit targetserver --gex-test=2000,3000,4000,5000
|
||||
.fi
|
||||
.RE
|
||||
|
||||
.LP
|
||||
To run a Diffie-Hellman Group Exchange modulus size test where 2048 bits is the minimum, 3072 bits is the preferred and 5000 bits is the maximum:
|
||||
.RS
|
||||
.nf
|
||||
ssh-audit targetserver --gex-test=2048:3072:5000
|
||||
.fi
|
||||
.RE
|
||||
|
||||
.LP
|
||||
To run a Diffie-Hellman Group Exchange modulus size test from 0 bits to 5120 bits in increments of 1024 bits:
|
||||
.RS
|
||||
.nf
|
||||
ssh-audit targetserver --gex-test=0-5120:1024
|
||||
.fi
|
||||
.RE
|
||||
|
||||
.SH RETURN VALUES
|
||||
When a successful connection is made and all algorithms are rated as "good", \fBssh-audit\fP returns 0. Other possible return values are:
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user