[Mimedefang] any comments?
Marco Berizzi
pupilla at hotmail.com
Tue Aug 27 11:54:00 EDT 2002
I have modified a bit the suggested minimum filter.
I have introduced a basic function so people inside the company must
compress their attach, before sending the e-mail.
/etc/mail/sendmail.cf set an absolute limit, both for in/out mail.
With this filter the e-mails from the internet are size-limited only by
sendmail.cf
The e-mails to the internet are 2 step size-limited.
There is the absolute size limit from sendmail.cf, and a soft size limit
from MD.
The filter rejects the e-mail if the size is major than a limit
($MaxOutSize) and contains attach not listed in $good_exts
The filter accept the fat e-mail if only contain attach with the ext =
$good_exts
Any comments?
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# -*- 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: suggested-minimum-filter-for-windows-clients,v 1.43 2002/08/23 19:16:29 dfs Exp $
#***********************************************************************
#***********************************************************************
# 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 at mydomain.com'
#***********************************************************************
#$AdminAddress = 'postmaster at localhost';
$AdminAddress = 'postmaster at XXX';
#$AdminName = "MIMEDefang Administrator's Full Name";
$AdminName = "MIMEDefang Administrator";
#***********************************************************************
# Set the e-mail address from which MIMEDefang quarantine warnings and
# user notifications appear to come. A good example would be
# 'mimedefang at mydomain.com'. Make sure to have an alias for this
# address if you want replies to it to work.
#***********************************************************************
#$DaemonAddress = 'mimedefang at localhost';
$DaemonAddress = 'postmaster at XXX';
#***********************************************************************
# 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;
#***********************************************************************
# Set various stupid things your mail client does below.
#***********************************************************************
# Set the next one if your mail client cannot handle nested multipart
# messages. DO NOT set this lightly; it will cause action_add_part to
# work rather strangely. Leave it at zero, even for MS Outlook, unless
# you have serious problems.
$Stupidity{"flatten"} = 0;
# Set the next one if your mail client cannot handle multiple "inline"
# parts.
$Stupidity{"NoMultipleInlines"} = 0;
# This is a list of permitted ext when the message is larger than
# $MaxOutSize
$MaxOutSize = 100*1024;
sub filter_good_filename ($) {
my($entity) = @_;
my($good_exts, $re);
# Good extensions
$good_exts = '\.(gz|zip|rar|bz2|tgz|tbz)$';
$re = $good_exts;
return re_match($entity, $re);
}
# This procedure returns true for entities with bad filenames.
sub filter_bad_filename ($) {
my($entity) = @_;
my($bad_exts, $re);
# Bad extensions
#$bad_exts = '(ade|adp|bas|bat|chm|cmd|com|cpl|crt|dll|exe|hlp|hta|inf|ini|ins|isp|jse?|lib|lnk|mdb|mde|msc|msi|msp|mst|ocx|pcd|pif|reg|scr|sct|shb|shs|sys|url|vb|vbe|vbs|vxd|wsc|wsf|wsh)';
$bad_exts = '(avi|asf|mp3|mpg|mpe|mpeg|mov|mng|ade|adp|bas|bat|chm|cmd|com|cpl|crt|dll|exe|hlp|hta|inf|ini|ins|isp|jse?|lib|lnk|mdb|mde|msc|msi|msp|mst|ocx|pcd|pif|reg|scr|sct|shb|shs|sys|url|vb|vbe|vbs|vxd|wsc|wsf|wsh)';
# Do not allow:
# - curlies
# - bad extensions (possibly with trailing dots) at end or
# followed by non-alphanum
$re = '(\{)|(\})|(\.' . $bad_exts . ')\.*([^-A-Za-z0-9_.]|$)';
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_nvcc() if ($Features{'Virus:NVCC'});
#return message_contains_virus_rav() if ($Features{'Virus:RAV'});
#return message_contains_virus_sophie() if ($Features{'Virus:SOPHIE'});
#return message_contains_virus_sophos() if ($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_clamav() if ($Features{'Virus:CLAMAV'});
return (wantarray ? (0, 'ok', 'ok') : 0);
}
# Scan for a virus using the first supported virus scanner we find.
sub entity_contains_virus ($) {
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 ($Features{'Virus:NAI'});
#return entity_contains_virus_nvcc($e) if ($Features{'Virus:NVCC'});
#return entity_contains_virus_rav($e) if ($Features{'Virus:RAV'});
#return entity_contains_virus_sophie($e) if ($Features{'Virus:SOPHIE'});
#return entity_contains_virus_sophos($e) if ($Features{'Virus:SOPHOS'});
#return entity_contains_virus_trend($e) if ($Features{'Virus:TREND'});
return entity_contains_virus_filescan($e) if ($Features{'Virus:FileScan'});
#return entity_contains_virus_clamav($e) if ($Features{'Virus:CLAMAV'});
return (wantarray ? (0, 'ok', 'ok') : 0);
}
#***********************************************************************
# %PROCEDURE: filter_begin
# %ARGUMENTS:
# None
# %RETURNS:
# Nothing
# %DESCRIPTION:
# Called just before e-mail parts are processed
#***********************************************************************
sub filter_begin () {
# ALWAYS drop messages with suspicious chars in headers
if ($SuspiciousCharsInHeaders) {
action_quarantine_entire_message();
action_notify_administrator("Message quarantined because of suspicious characters in headers");
# Do NOT allow message to reach recipient(s)
return action_discard();
}
if ($RelayAddr eq "172.16.1.227" or
$RelayAddr eq "172.18.1.13" or
$RelayAddr eq "172.17.1.13" or
$RelayAddr eq "172.22.1.14" or
$RelayAddr eq "172.21.1.14")
{
$LocalRelay = 1;
} else {
$LocalRelay = 0;
}
# Scan for viruses if any virus-scanners are installed
my($code, $category, $action) = message_contains_virus();
$FoundVirus = ($category eq "virus");
}
#***********************************************************************
# %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
# Reject Korean Mail
$head = $entity->head;
$charset = $head->mime_attr("content-type.charset");
if (defined($charset)) {
$charset =~ tr/A-Z/a-z/;
if ($charset eq "ks_c_5601-1987" or
$charset eq "euc-kr") {
return action_bounce("Spam from Korea not accepted.");
}
}
# Virus scan
if ($FoundVirus) {
my($code, $category, $action);
$VirusScannerMessages = "";
($code, $category, $action) = entity_contains_virus($entity);
if ($category eq "virus") {
#return action_quarantine($entity, "A known virus was discovered and deleted. Virus-scanner messages follow:\n$VirusScannerMessages\n\n");
if (!$LocalRelay) {
return action_drop_with_warning("Un virus e' stato scoperto e cancellato. Segue il messaggio dell'antivirus:\n$VirusScannerMessages\n\n");
} else {
action_notify_administrator("Message bounced with virus $VirusScannerMessages");
return action_bounce("Il messaggio e' stato rifiutato perche' e` presente un Virus");
}
}
}
if (filter_bad_filename($entity)) {
if (!LocalRelay) {
#return action_quarantine($entity, "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_drop_with_warning("Un allegato chiamato $fname e' stato rimosso da questo documento\ndato che si tratta di un allegato pericoloso. Se hai bisogno di questo\ndocumento contatta il mittente.\n");
} else {
return action_bounce("Il messaggio e' stato rifiutato perche' e` presente un allegato pericoloso chiamato $fname");
}
}
# eml is bad if it's not multipart
if (re_match($entity, '\.eml')) {
if (!LocalRelay) {
#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");
return action_drop_with_warning("Un allegato non-multipart chiamato $fname e' stato rimosso da questo documento\ndato che si tratta di un allegato pericoloso. Se hai bisogno di questo\ndocumento contatta il mittente.\n");
} else {
return action_bounce("Il messaggio e' stato rifiutato perche' e` presente un allegato non-multipart chiamato $fname");
}
}
# Clean up HTML if Anomy::HTMLCleaner is installed.
if (!$LocalRelay) {
if ($Features{"HTMLCleaner"}) {
if ($type eq "text/html") {
return anomy_clean_html($entity);
}
}
}
# Usually people break my balls because I restrict the
# message size. OK: I have changed the limit.
# Italian people are lazy. I have never seen a compressed
# attach in an e-mail, so this time ball-breakers *MUST* compress the
# attach if the message is bigger than $MaxOutSize
if ($LocalRelay) {
if (-s "./INPUTMSG" > $MaxOutSize) {
if (filter_good_filename($entity)
or
($type =~ m+^text/+) or
($type eq "text")
)
{
return action_accept();
} else {
return action_bounce("You are lazy! Compress the attach");
}
}
}
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 (!$LocalRelay) {
if (filter_bad_filename($entity)) {
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");
return action_drop_with_warning("Un allegato di tipo $type, chiamato $fname e' stato rimosso da questo documento\ndato che si tratta di un allegato pericoloso. Se hai bisogno di questo documento\ncontatta il mittente.\n");
}
# eml is bad if it's not message/rfc822
if (re_match($entity, '\.eml') and ($type ne "message/rfc822")) {
#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");
return action_drop_with_warning("Un allegato di tipo non-message/rfc822, chiamato $fname e' stato rimosso da questo documento\ndato che si tratta di un allegato pericoloso. Se hai bisogno di questo documento\ncontatta il mittente.\n");
}
return action_accept();
}
if ($LocalRelay) {
if (filter_bad_filename($entity)) {
action_notify_administrator("Message bounced because of A MULTIPART attachment of type $type, named $fname");
#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");
return action_bounce("Il messaggio e' stato rifiutato perche' contiene un allegato di tipo $type, chiamato $fname");
}
# eml is bad if it's not message/rfc822
if (re_match($entity, '\.eml') and ($type ne "message/rfc822")) {
#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");
return action_bounce("Il messaggio e' stato rifiutato perche' contiene un allegato di tipo non-message/rfc822, chiamato $fname");
}
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) = @_;
# No sense doing any extra work
return if message_rejected();
# Spam checks if SpamAssassin is installed
if (!$LocalRelay) {
if ($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, $report) = spam_assassin_check();
if ($hits >= $req) {
my($score);
if ($hits < 20) {
$score = "*" x int($hits);
} else {
$score = "*" x 20;
}
# We add a header which looks like this:
# X-Spam-Score: 6.8 (******) NAME_OF_TEST,NAME_OF_TEST
# The number of asterisks in parens is the integer part
# of the spam score clamped to a maximum of 40.
# MUA filters can easily be written to trigger on a
# minimum number of asterisks...
if ($hits >= 25) {
action_bounce("We don't accept SPAM");
}
action_change_header("Subject", "***SPAM*** $Subject ($score)");
action_change_header("X-Spam-Score", "$hits ($score) $names");
# If you find the SA report useful, add it, I guess...
action_add_part($entity, "text/plain", "-suggest",
"$report\n",
"SpamAssassinReport.txt", "inline");
}
}
}
}
}
# DO NOT delete the next line, or Perl will complain.
1;
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