[Mimedefang] MX -> 127.0.0.1

[Matthew.van.Eerde at hbinc.com]

David F. Skoll wrote:
> Les Mikesell wrote:
> 
>> Any MX of 127.0.0.1 is not only broken but malicious
> 
> I would reject mail from a domain that does that.

So in principle...

sub filter_sender
{	...
	if (	any_illegal_mxs_for($sender) )
	{
		# Les-style
		# let's defuse that bomb
		action_discard(...);

		# Matt-style
		# let's throw the bomb back over the wall
		action_reject(
			"MX for $sender " .
			"includes IP $bad_mx " .
			"in illegal subnet $bad_subnet"
		);
	}
	...
}

sub any_illegal_mxs_for($)
{
	my $email = shift;
	my $domain = domain_of($email);
	my @mxs = mxs_for($domain);

	for my $mx (@mxs)
	{
		if (is_illegal($mx))
		{
			$bad_mx = $mx;
			return 1; # yup, there's at least one
		}
	}

	return 0; # nope, they all check out
}

my @bad_subnets = (...);

sub is_illegal($)
{
	my $ip = shift;
	for my $subnet (@bad_subnets)
	{
		if (ip_in_subnet($ip, $subnet))
		{
			$bad_subnet = $subnet;
			return 1; # yup, illegal
		}
	}

	return 0; # nah, this ip is fine
}

-- 
Matthew.van.Eerde (at) hbinc.com               805.964.4554 x902
Hispanic Business Inc./HireDiversity.com       Software Engineer