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Top level domains (TLDs) that use wildcards are bad. Or rather, some people consider it poor form. Other people think it's ok. If you think it's bad, the following script will print out the wildcard addresses of all the TLDs that currently employ wildcards.

For instance, try looking up the addresses of the following hosts (at the time of writing, the .museum TLD uses wildcards):

% host has address % host has address

(And I can assure you that these sites do not exists). If you want to know which TLDs use the above trickery, then the following script is for you.

Note: you will need to install Net::DNS and Net::Domain::TLD beforehand.

#! /usr/local/bin/perl -w use strict; use vars '$VERSION'; $VERSION = '1.00'; use Net::DNS; use Net::Domain::TLD; use Socket 'inet_ntoa'; # the script takes a long time to run: set to 1 if you # want to see what is happening. use constant VERBOSE => 0; # look for 4 bogus hostnames (pray they don't really exist) my @bogus = ( join( '' => map { ('a'..'z', 0..9)[rand 36] } 1..24 ), join( '' => map { ('a'..'z', 0..9)[rand 36] } 1..24 ), join( '' => map { ('a'..'z', 0..9)[rand 36] } 1..24 ), join( '' => map { ('a'..'z', 0..9)[rand 36] } 1..24 ), ); my $resolv = Net::DNS::Resolver->new; for my $tld ( sort Net::Domain::TLD->new->All ) { warn ".$tld\n" if VERBOSE; my %ip; for my $dom ( @bogus) { my $host = "$dom.$tld"; if( my $addr = gethostbyname( $host )) { # got an IP address on a hostname $ip{inet_ntoa($addr)}++; } } # skip the rest if all we received were NXDOMAINs. next unless keys %ip; # see the nature of their sins my $domain = "$bogus[0].$tld"; if( my $rr = $resolv->query( $domain, 'MX' )) { for my $mx( $rr->answer ) { next unless $mx->type eq 'MX'; my @addr = get_a( $resolv, $mx->exchange ); @addr or @addr = get_a( $resolv, $domain ); print ".$tld $_\n" for @addr; } } else { # no MX records for the host, try A records. print ".$tld $_\n" for get_a($resolv, $domain); } } sub get_a { my $resolv = shift; my $rec = shift; my @rr; if( my $rr = $resolv->query( $rec, 'A' )) { $_->type eq 'A' and push @rr, $_->address for $rr->answer; } @rr; } =head1 NAME tldwild - list all DNS TLDs that employ wildcards =head1 SYNOPSIS B<tldwild> No command line options are recognised. =head1 DESCRIPTION In the Domain Name System, a query for a host name that does not map to an IP address should return an NXDOMAIN (no such domain) error. Sometimes, within an organisation, it is useful to declare "wildcard" records, in order to map an arbitrary number of host names onto a single server. Some organisations that manage top-level domains (TLDs) also employ such records in an attempt to guide web users who type addresses incorrectly to a single web page where they may find help. (This was the basis of the 2003 Verisign .com/.net wildcard scandal). For small TLDs, this was never much of a problem, but the times they are a-changing. If a spammer uses a sender envelope and HELO connect strings based on inexistent hostnames in these smaller TLDs, and if you perform a lookup on these addresses, they will resolve correctly. The information produced by this script allows you to make better decisions as to whether an address is legitimate or not. This is version 1.00. =head1 EXAMPLES Piping the output of this script through the following one-liner: perl -lane 'print "$F[1]\tREJECT .$F[0] MX wildcard"' ...will produce a Postfix access map suitable for a C<check_sender_mx_access> restriction. Recipes for other MTAs are welcome. =head1 SEE ALSO This script uses code that is documented in L<Net::DNS> and L<Net::Domain::TLD>. RFC 974 - Mail routing and the domain system RFC 1035 - Domain names - implementation and specification =head1 BUGS The script does not deal with MX records that return numeric IP addresses (but this is a violation of the RFC standard anyway, and no TLD appears to do so at present). =head1 AUTHOR David Landgren, eval {join chr(0x40) => qw{david}} =head1 COPYRIGHT Copyright (c) 2005 David Landgren. This script is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

At the time of writing, the script produced the following output:

.cx .mp .museum .nu .nu .ph .pw .tk .tk .ws

- another intruder with the mooring in the heart of the Perl

In reply to tldwild - display TLDs that employ DNS wildcards by grinder

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