mimedefang 2.75-1 / etc / mimedefang-filter

# -*- Perl -*-
#***********************************************************************
#
# mimedefang-filter
#
# Suggested minimum-protection filter for Microsoft Windows clients, plus
# SpamAssassin checks if SpamAssassin is installed.
#
# Copyright (C) 2002 Roaring Penguin Software Inc.
#
# This program may be distributed under the terms of the GNU General
# Public License, Version 2, or (at your option) any later version.
#
# $Id$
#***********************************************************************

#***********************************************************************
# Set administrator's e-mail address here.  The administrator receives
# quarantine messages and is listed as the contact for site-wide
# MIMEDefang policy.  A good example would be 'defang-admin@mydomain.com'
#***********************************************************************
$AdminAddress = 'postmaster@localhost';
$AdminName = "MIMEDefang Administrator's Full Name";

#***********************************************************************
# Set the e-mail address from which MIMEDefang quarantine warnings and
# user notifications appear to come.  A good example would be
# 'mimedefang@mydomain.com'.  Make sure to have an alias for this
# address if you want replies to it to work.
#***********************************************************************
$DaemonAddress = 'mimedefang@localhost';

#***********************************************************************
# If you set $AddWarningsInline to 1, then MIMEDefang tries *very* hard
# to add warnings directly in the message body (text or html) rather
# than adding a separate "WARNING.TXT" MIME part.  If the message
# has no text or html part, then a separate MIME part is still used.
#***********************************************************************
$AddWarningsInline = 0;

#***********************************************************************
# To enable syslogging of virus and spam activity, add the following
# to the filter:
# md_graphdefang_log_enable();
# You may optionally provide a syslogging facility by passing an
# argument such as:  md_graphdefang_log_enable('local4');  If you do this, be
# sure to setup the new syslog facility (probably in /etc/syslog.conf).
# An optional second argument causes a line of output to be produced
# for each recipient (if it is 1), or only a single summary line
# for all recipients (if it is 0.)  The default is 1.
# Comment this line out to disable logging.
#***********************************************************************
md_graphdefang_log_enable('mail', 1);

#***********************************************************************
# Uncomment this to block messages with more than 50 parts.  This will
# *NOT* work unless you're using Roaring Penguin's patched version
# of MIME tools, version MIME-tools-5.411a-RP-Patched-02 or later.
#
# WARNING: DO NOT SET THIS VARIABLE unless you're using at least
# MIME-tools-5.411a-RP-Patched-02; otherwise, your filter will fail.
#***********************************************************************
# $MaxMIMEParts = 50;

#***********************************************************************
# Set various stupid things your mail client does below.
#***********************************************************************

# Set the next one if your mail client cannot handle multiple "inline"
# parts.
$Stupidity{"NoMultipleInlines"} = 0;

# Detect and load Perl modules
detect_and_load_perl_modules();

# This procedure returns true for entities with bad filenames.
sub filter_bad_filename  {
    my($entity) = @_;
    my($bad_exts, $re);

    # Bad extensions
    $bad_exts = '(ade|adp|app|asd|asf|asx|bas|bat|chm|cmd|com|cpl|crt|dll|exe|fxp|hlp|hta|hto|inf|ini|ins|isp|jse?|lib|lnk|mdb|mde|msc|msi|msp|mst|ocx|pcd|pif|prg|reg|scr|sct|sh|shb|shs|sys|url|vb|vbe|vbs|vcs|vxd|wmd|wms|wmz|wsc|wsf|wsh|\{[^\}]+\})';

    # Do not allow:
    # - CLSIDs  {foobarbaz}
    # - bad extensions (possibly with trailing dots) at end
    $re = '\.' . $bad_exts . '\.*$';

    return 1 if (re_match($entity, $re));

    # Look inside ZIP files
    if (re_match($entity, '\.zip$') and
	$Features{"Archive::Zip"}) {
	my $bh = $entity->bodyhandle();
	if (defined($bh)) {
	    my $path = $bh->path();
	    if (defined($path)) {
		return re_match_in_zip_directory($path, $re);
	    }
	}
    }
    return 0;
}

#***********************************************************************
# %PROCEDURE: filter_begin
# %ARGUMENTS:
#  $entity -- the parsed MIME::Entity
# %RETURNS:
#  Nothing
# %DESCRIPTION:
#  Called just before e-mail parts are processed
#***********************************************************************
sub filter_begin {
    my($entity) = @_;
    # ALWAYS drop messages with suspicious chars in headers
    if ($SuspiciousCharsInHeaders) {
        md_graphdefang_log('suspicious_chars');
	# action_quarantine_entire_message("Message quarantined because of suspicious characters in headers");
	# Do NOT allow message to reach recipient(s)
	return action_discard();
    }

    # Copy original message into work directory as an "mbox" file for
    # virus-scanning
    md_copy_orig_msg_to_work_dir_as_mbox_file();

    # Scan for viruses if any virus-scanners are installed
    my($code, $category, $action) = message_contains_virus();

    # Lower level of paranoia - only looks for actual viruses
    $FoundVirus = ($category eq "virus");

    # Higher level of paranoia - takes care of "suspicious" objects
    # $FoundVirus = ($action eq "quarantine");

    if ($FoundVirus) {
	md_graphdefang_log('virus', $VirusName, $RelayAddr);
	md_syslog('warning', "Discarding because of virus $VirusName");
	return action_discard();
    }

    if ($action eq "tempfail") {
	action_tempfail("Problem running virus-scanner");
	md_syslog('warning', "Problem running virus scanner: code=$code, category=$category, action=$action");
    }
}

#***********************************************************************
# %PROCEDURE: filter
# %ARGUMENTS:
#  entity -- a Mime::Entity object (see MIME-tools documentation for details)
#  fname -- the suggested filename, taken from the MIME Content-Disposition:
#           header.  If no filename was suggested, then fname is ""
#  ext -- the file extension (everything from the last period in the name
#         to the end of the name, including the period.)
#  type -- the MIME type, taken from the Content-Type: header.
#
#  NOTE: There are two likely and one unlikely place for a filename to
#  appear in a MIME message:  In Content-Disposition: filename, in
#  Content-Type: name, and in Content-Description.  If you are paranoid,
#  you will use the re_match and re_match_ext functions, which return true
#  if ANY of these possibilities match.  re_match checks the whole name;
#  re_match_ext checks the extension.  See the sample filter below for usage.
# %RETURNS:
#  Nothing
# %DESCRIPTION:
#  This function is called once for each part of a MIME message.
#  There are many action_*() routines which can decide the fate
#  of each part; see the mimedefang-filter man page.
#***********************************************************************
sub filter {
    my($entity, $fname, $ext, $type) = @_;

    return if message_rejected(); # Avoid unnecessary work

    # Block message/partial parts
    if (lc($type) eq "message/partial") {
        md_graphdefang_log('message/partial');
	action_bounce("MIME type message/partial not accepted here");
	return action_discard();
    }

    if (filter_bad_filename($entity)) {
        md_graphdefang_log('bad_filename', $fname, $type);
	return action_drop_with_warning("An attachment named $fname was removed from this document as it\nconstituted a security hazard.  If you require this document, please contact\nthe sender and arrange an alternate means of receiving it.\n");
    }

    return action_accept();
}

#***********************************************************************
# %PROCEDURE: filter_multipart
# %ARGUMENTS:
#  entity -- a Mime::Entity object (see MIME-tools documentation for details)
#  fname -- the suggested filename, taken from the MIME Content-Disposition:
#           header.  If no filename was suggested, then fname is ""
#  ext -- the file extension (everything from the last period in the name
#         to the end of the name, including the period.)
#  type -- the MIME type, taken from the Content-Type: header.
# %RETURNS:
#  Nothing
# %DESCRIPTION:
#  This is called for multipart "container" parts such as message/rfc822.
#  You cannot replace the body (because multipart parts have no body),
#  but you should check for bad filenames.
#***********************************************************************
sub filter_multipart {
    my($entity, $fname, $ext, $type) = @_;

    return if message_rejected(); # Avoid unnecessary work

    if (filter_bad_filename($entity)) {
        md_graphdefang_log('bad_filename', $fname, $type);
	action_notify_administrator("A MULTIPART attachment of type $type, named $fname was dropped.\n");
	return action_drop_with_warning("An attachment of type $type, named $fname was removed from this document as it\nconstituted a security hazard.  If you require this document, please contact\nthe sender and arrange an alternate means of receiving it.\n");
    }

    # Block message/partial parts
    if (lc($type) eq "message/partial") {
        md_graphdefang_log('message/partial');
	action_bounce("MIME type message/partial not accepted here");
	return;
    }

    return action_accept();
}


#***********************************************************************
# %PROCEDURE: defang_warning
# %ARGUMENTS:
#  oldfname -- the old file name of an attachment
#  fname -- the new "defanged" name
# %RETURNS:
#  A warning message
# %DESCRIPTION:
#  This function customizes the warning message when an attachment
#  is defanged.
#***********************************************************************
sub defang_warning {
    my($oldfname, $fname) = @_;
    return
	"An attachment named '$oldfname' was converted to '$fname'.\n" .
	"To recover the file, right-click on the attachment and Save As\n" .
	"'$oldfname'\n";
}

# If SpamAssassin found SPAM, append report.  We do it as a separate
# attachment of type text/plain
sub filter_end {
    my($entity) = @_;

    # If you want quarantine reports, uncomment next line
    # send_quarantine_notifications();

    # IMPORTANT NOTE:  YOU MUST CALL send_quarantine_notifications() AFTER
    # ANY PARTS HAVE BEEN QUARANTINED.  SO IF YOU MODIFY THIS FILTER TO
    # QUARANTINE SPAM, REWORK THE LOGIC TO CALL send_quarantine_notifications()
    # AT THE END!!!

    # No sense doing any extra work
    return if message_rejected();

    # Spam checks if SpamAssassin is installed
    if ($Features{"SpamAssassin"}) {
	if (-s "./INPUTMSG" < 100*1024) {
	    # Only scan messages smaller than 100kB.  Larger messages
	    # are extremely unlikely to be spam, and SpamAssassin is
	    # dreadfully slow on very large messages.
	    my($hits, $req, $names, $report) = spam_assassin_check();
	    my($score);
	    if ($hits < 40) {
		$score = "*" x int($hits);
	    } else {
		$score = "*" x 40;
	    }
	    # We add a header which looks like this:
	    # X-Spam-Score: 6.8 (******) NAME_OF_TEST,NAME_OF_TEST
	    # The number of asterisks in parens is the integer part
	    # of the spam score clamped to a maximum of 40.
	    # MUA filters can easily be written to trigger on a
	    # minimum number of asterisks...
	    if ($hits >= $req) {
		action_change_header("X-Spam-Score", "$hits ($score) $names");
                md_graphdefang_log('spam', $hits, $RelayAddr);

		# If you find the SA report useful, add it, I guess...
		action_add_part($entity, "text/plain", "-suggest",
		                "$report\n",
				"SpamAssassinReport.txt", "inline");
	    } else {
		# Delete any existing X-Spam-Score header?
		action_delete_header("X-Spam-Score");
	    }
	}
    }

    # I HATE HTML MAIL!  If there's a multipart/alternative with both
    # text/plain and text/html parts, nuke the text/html.  Thanks for
    # wasting our disk space and bandwidth...

    # If you want to strip out HTML parts if there is a corresponding
    # plain-text part, uncomment the next line.
    # remove_redundant_html_parts($entity);

    md_graphdefang_log('mail_in');

    # Deal with malformed MIME.
    # Some viruses produce malformed MIME messages that are misinterpreted
    # by mail clients.  They also might slip under the radar of MIMEDefang.
    # If you are worried about this, you should canonicalize all
    # e-mail by uncommenting the action_rebuild() line.  This will
    # force _all_ messages to be reconstructed as valid MIME.  It will
    # increase the load on your server, and might break messages produced
    # by marginal software.  Your call.

    # action_rebuild();
}

# DO NOT delete the next line, or Perl will complain.
1;