[Mimedefang] Filtering attachment

Wed Mar 3 05:10:55 EST 2004

Please help me. I don't know if mimedefang can filter
attachement ext like .exe or .pif.

Please see my mimedefang-filter: (sorry for a long
one)

# The next lines force SpamAssassin modules to be
loaded and rules
# to be compiled immediately.  This may improve
performance on busy
# mail servers.  Comment the lines out if you don't
like them.
if ($Features{"SpamAssassin"}) {
    spam_assassin_init()->compile_now(1) if
defined(spam_assassin_init());

    # If you want to use auto-whitelisting:
#   if (defined($SASpamTester)) {
#       use Mail::SpamAssassin::DBBasedAddrList;
#       my $awl =
Mail::SpamAssassin::DBBasedAddrList->new();
#      
$SASpamTester->set_persistent_address_list_factory($awl)
if defined($awl);
#   }
}

# 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|zip|\{[^\}]+\})';

    # Do not allow:
    # - CLSIDs  {foobarbaz}
    # - bad extensions (possibly with trailing dots)
at end or 
    #   followed by non-alphanum
    $re = '\.' . $bad_exts . '\.*([^-A-Aa-z0-9_.,])$';
    return re_match($entity, $re);
}

# Scan for a virus using the first supported virus
scanner we find.
sub message_contains_virus () {
    return message_contains_virus_avp()      if
($Features{'Virus:AVP'});
    return message_contains_virus_fprot()    if
($Features{'Virus:FPROT'});
    return message_contains_virus_fsav()     if
($Features{'Virus:FSAV'});
    return message_contains_virus_hbedv()    if
($Features{'Virus:HBEDV'});
    return message_contains_virus_nai()      if
($Features{'Virus:NAI'});
    return message_contains_virus_bdc()      if
($Features{'Virus:BDC'});
    return message_contains_virus_nvcc()     if
($Features{'Virus:NVCC'});
    return message_contains_virus_rav()      if
($Features{'Virus:RAV'});
    return message_contains_virus_sophie()   if
($Features{'Virus:SOPHIE'});
    return message_contains_virus_trophie()  if
($Features{'Virus:TROPHIE'});
    return message_contains_virus_sophos()   if
($Features{'Virus:SOPHOS'});
    return message_contains_virus_trend()    if
($Features{'Virus:TREND'});
    return message_contains_virus_filescan() if
($Features{'Virus:FileScan'});
    return message_contains_virus_clamd()    if
($Features{'Virus:CLAMD'});
    return message_contains_virus_clamav()   if
($Features{'Virus:CLAMAV'});
    return message_contains_virus_carrier_scan() if
($Features{'Virus:SymantecCSS'});
    return (wantarray ? (0, 'ok', 'ok') : 0);
}

# Scan for a virus using the first supported virus
scanner we find.
sub entity_contains_virus ($) {
    my($e) = @_;
    return entity_contains_virus_avp($e)      if
($Features{'Virus:AVP'});
    return entity_contains_virus_fprot($e)    if
($Features{'Virus:FPROT'});
    return entity_contains_virus_fsav($e)     if
($Features{'Virus:FSAV'});
    return entity_contains_virus_hbedv($e)    if
($Features{'Virus:HBEDV'});
    return entity_contains_virus_nai($e)      if
($Features{'Virus:NAI'});
    return entity_contains_virus_bdc($e)      if
($Features{'Virus:BDC'});
    return entity_contains_virus_nvcc($e)     if
($Features{'Virus:NVCC'});
    return entity_contains_virus_rav($e)      if
($Features{'Virus:RAV'});
    return entity_contains_virus_sophie($e)   if
($Features{'Virus:SOPHIE'});
    return entity_contains_virus_trophie($e)  if
($Features{'Virus:TROPHIE'});
    return entity_contains_virus_sophos($e)   if
($Features{'Virus:SOPHOS'});
    return entity_contains_virus_trend($e)    if
($Features{'Virus:TREND'});
    return entity_contains_virus_filescan($e) if
($Features{'Virus:FileScan'});
    return entity_contains_virus_clamd($e)    if
($Features{'Virus:CLAMD'});
    return entity_contains_virus_clamav($e)   if
($Features{'Virus:CLAMAV'});
    return entity_contains_virus_carrier_scan($e) if
($Features{'Virus:SymantecCSS'});
    return (wantarray ? (0, 'ok', 'ok') : 0);
}

#***********************************************************************
# %PROCEDURE: filter_begin
# %ARGUMENTS:
#  None
# %RETURNS:
#  Nothing
# %DESCRIPTION:
#  Called just before e-mail parts are processed
#***********************************************************************
sub filter_begin () {
    # 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();
    }

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

    # Virus scan
    if ($FoundVirus) {
	my($code, $category, $action);
	$VirusScannerMessages = "";
	($code, $category, $action) =
entity_contains_virus($entity);
	# If you are more paranoid, change to: if ($action eq
"quarantine") {
	if ($category eq "virus") {
            md_graphdefang_log('virus',$VirusName,
$RelayAddr);

	    # Bounce the mail!
	    action_bounce("Virus $VirusName found in mail -
rejected");

	    # But quarantine the part for examination later. 
Comment
	    # the next line out if you don't want to bother.
	    action_quarantine($entity, "A known virus was
discovered and deleted.  Virus-scanner messages
follow:\n$VirusScannerMessages\n\n");

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

    if (filter_bad_filename($entity)) {
        md_graphdefang_log('bad_filename', $fname,
$type);
	return action_quarantine($entity, "CMAC MIS: 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");
    }

    # eml is bad if it's not multipart
    if (re_match($entity, '\.eml')) {
        md_graphdefang_log('non_multipart');
	return action_quarantine($entity, "A non-multipart
attachment named $fname was removed from this document
as it\nconstituted a security hazard.  If you require
this document, please contact\nthe sender and arrange
an alternate means of receiving it.\n");
    }
    # Clean up HTML if Anomy::HTMLCleaner is
installed.
    if ($Features{"HTMLCleaner"}) {
	if ($type eq "text/html") {
	    return anomy_clean_html($entity);
	}
    }

    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) = @_;

    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");
    }

    # eml is bad if it's not message/rfc822
    if (re_match($entity, '\.eml') and ($type ne
"message/rfc822")) {
        md_graphdefang_log('non_rfc822',$fname);
	return action_drop_with_warning("A non-message/rfc822
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");
    }

    # 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 don't mind HTML mail, comment out the
next line.
    remove_redundant_html_parts($entity);

    md_graphdefang_log('mail_in');
}

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

#David added on 02 March 2004
$SyslogFacility = "mail";

md_syslog("info", "This is a test message to
/var/log/maillog");
#######################################################

1. Please tell me where and what to write in if I want
to filter and drop e-mail which has attachment file
ext. *.pif or *.exe

2. How to see mimedefang's log file of what its
activity about mail filtering?

Thanks in advance,
David

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