[Mimedefang] Strip DOC with macros

David F. Skoll dfs at roaringpenguin.com
Wed Feb 25 14:08:55 EST 2015


On Wed, 25 Feb 2015 13:17:42 -0500 (EST)
Justin Edmands <j.edmands at sagedining.com> wrote:

> I wanted to know if I could use mimedefang to strip
> out .DOC, .DOCX, .XLS, and .XLSX files (or any applicable file type)
> if they contain a macro.

Yes.  Stripping attachments is explained in the mimedefang-filter page.
The important part is detecting macros.  Here's code we have to do it.
(This is a code fragment just to give you the idea.  You'll need to modify
it to integrate it with MIMEDefang.)

Regards,

David.


==============================================================================
# These markers were documented at:
# http://blog.rootshell.be/2015/01/08/searching-for-microsoft-office-files-containing-macro/
# as of 2015-01-15
# $entity is a MIME::Entity that's the parsed message

my $marker1 = "\xd0\xcf\x11\xe0";
my $marker2 = "\x00\x41\x74\x74\x72\x69\x62\x75\x74\x00";

sub contains_office_macros
{
	my ($self, $entity) = @_;
	my @parts = $entity->parts();
	if (scalar(@parts) > 0) {
		foreach my $part (@parts) {
			if ($self->contains_office_macros($part)) {
				return 1;
			}
		}
		return 0;
	}
	my $is_msoffice_extension = 0;
	foreach my $attr_name (qw( Content-Disposition.filename Content-Type.name) ) {
		my $possible = $entity->head->mime_attr($attr_name);
		$possible = decode_mimewords($possible);
		if ($possible =~ /\.(doc|docx)$/i) {
			$is_msoffice_extension = 1;
			last;
		}
	}
	return 0 unless $is_msoffice_extension;
	return 0 unless defined($entity->bodyhandle) && defined($entity->bodyhandle->path);
	my $fp;
	if (!open($fp, '<:raw', $entity->bodyhandle->path)) {
		return 0;
	}
	my $contents;
	{
		local $/;
		$contents = <$fp>;
		close($fp);
	}
	if (index($contents, $marker1) > -1 &&
	    index($contents, $marker2) > -1) {
		return 1;
	}
	return 0;
}


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