Add user-desc module
Add the user-desc module that obtains user descriptions from Active Directory.main
TNeitzel
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from pathlib import Path
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from datetime import datetime
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from impacket.ldap import ldap, ldapasn1
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from impacket.ldap.ldap import LDAPSearchError
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class CMEModule:
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'''
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Get user descriptions stored in Active Directory.
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Module by Tobias Neitzel (@qtc_de)
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'''
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name = 'user-desc'
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description = 'Get user descriptions stored in Active Directory'
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supported_protocols = ['ldap']
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opsec_safe = True
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multiple_hosts = True
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def options(self, context, module_options):
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'''
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LDAP_FILTER Custom LDAP search filter (fully replaces the default search)
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DESC_FILTER An additional seach filter for descriptions (supports wildcard *)
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DESC_INVERT An additional seach filter for descriptions (shows non matching)
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USER_FILTER An additional seach filter for usernames (supports wildcard *)
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USER_INVERT An additional seach filter for usernames (shows non matching)
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KEYWORDS Use a custom set of keywords (comma separated)
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ADD_KEYWORDS Add additional keywords to the default set (comma separated)
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'''
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self.log_file = None
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self.desc_count = 0
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self.context = context
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self.account_names = set()
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self.keywords = {'pass', 'creds', 'creden', 'key', 'secret', 'default'}
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if 'LDAP_FILTER' in module_options:
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self.search_filter = module_options['LDAP_FILTER']
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else:
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self.search_filter = '(&(objectclass=user)'
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if 'DESC_FILTER' in module_options:
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self.search_filter += '(description={})'.format(module_options['DESC_FILTER'])
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if 'DESC_INVERT' in module_options:
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self.search_filter += '(!(description={}))'.format(module_options['DESC_INVERT'])
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if 'USER_FILTER' in module_options:
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self.search_filter += '(sAMAccountName={})'.format(module_options['USER_FILTER'])
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if 'USER_INVERT' in module_options:
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self.search_filter += '(!(sAMAccountName={}))'.format(module_options['USER_INVERT'])
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self.search_filter += ')'
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if 'KEYWORDS' in module_options:
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self.keywords = set(module_options['KEYWORDS'].split(','))
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elif 'ADD_KEYWORDS' in module_options:
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add_keywords = set(module_options['ADD_KEYWORDS'].split(','))
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self.keywords = self.keywords.union(add_keywords)
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def __del__(self):
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'''
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Destructor - closes the log file.
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'''
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try:
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self.log_file.close()
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info = 'Saved {} user descriptions to {}'.format(self.desc_count, self.log_file.name)
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self.context.log.highlight(info)
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except AttributeError:
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pass
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def on_login(self, context, connection):
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'''
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On successful LDAP login we perform a search for all user objects that have a description.
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Users can specify additional LDAP filters that are applied to the query.
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'''
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self.create_log_file(connection.conn.getRemoteHost(), datetime.now().strftime("%Y%m%d_%H%M%S"))
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context.log.debug("Starting LDAP search with search filter '{}'".format(self.search_filter))
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try:
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sc = ldap.SimplePagedResultsControl()
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connection.ldapConnection.search(searchFilter=self.search_filter,
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attributes=['sAMAccountName', 'description'],
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sizeLimit=0, searchControls=[sc],
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perRecordCallback=self.process_record)
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except LDAPSearchError as e:
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context.log.error('Obtained unexpected exception: {}'.format(str(e)))
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def create_log_file(self, host, time):
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'''
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Create a log file for dumping user descriptions.
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'''
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logfile = 'UserDesc-{}-{}.log'.format(host, time)
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logfile = Path.home().joinpath('.cme').joinpath('logs').joinpath(logfile)
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self.context.log.debug("Creating log file '{}'".format(logfile))
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self.log_file = open(logfile, 'w')
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self.append_to_log("User:", "Description:")
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def append_to_log(self, user, description):
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'''
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Append a new entry to the log file. Helper function that is only used to have an
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unified padding on the user field.
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'''
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print(user.ljust(25), description, file=self.log_file)
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def process_record(self, item):
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'''
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Function that is called to process the items obtained by the LDAP search. All items are
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written to the log file per default. Items that contain one of the keywords configured
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within this module are also printed to stdout.
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On large Active Directories there seems to be a problem with duplicate user entries. For
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some reason the process_record function is called multiple times with the same user entry.
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Not sure whether this is a fault by this module or by impacket. As a workaround, this
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function adds each new account name to a set and skips accounts that have already been added.
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'''
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if not isinstance(item, ldapasn1.SearchResultEntry):
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return
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sAMAccountName = ''
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description = ''
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try:
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for attribute in item['attributes']:
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if str(attribute['type']) == 'sAMAccountName':
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sAMAccountName = attribute['vals'][0].asOctets().decode('utf-8')
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elif str(attribute['type']) == 'description':
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description = attribute['vals'][0].asOctets().decode('utf-8')
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except Exception as e:
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entry = sAMAccountName or 'item'
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self.context.error("Skipping {}, cannot process LDAP entry due to error: '{}'".format(entry, str(e)))
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if description and sAMAccountName not in self.account_names:
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self.desc_count += 1
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self.append_to_log(sAMAccountName, description)
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if self.highlight(description):
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self.context.log.highlight('User: {} - Description: {}'.format(sAMAccountName, description))
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self.account_names.add(sAMAccountName)
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def highlight(self, description):
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'''
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Check for interesting entries. Just checks whether certain keywords are contained within the
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user description. Keywords are configured at the top of this class within the options function.
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It is tempting to implement more logic here (e.g. catch all strings that are longer than seven
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characters and contain 3 different character classes). Such functionality is nice when playing
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CTF in small AD environments. When facing a real AD, such functionality gets annoying, because
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it generates to much output with 99% of it being false positives.
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The recommended way when targeting user descriptions is to use the keyword filter to catch low
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hanging fruites. More dedicated searches for sensitive information should be done using the logfile.
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This allows you to refine your search query at any time without having to pull data from AD again.
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'''
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for keyword in self.keywords:
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if keyword.lower() in description.lower():
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return True
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return False
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