[Mimedefang] action_rebuild()

[Marco Berizzi]

I have just upgraded to MIMEDefang 2.5
I'm experimenting a little problem with the function action_rebuild()
I'm using Slackware 8.0 + sendmail 8.12.2 to forward all the mail to an
internal M$-Exchange Server 5.5.

Now when someone send a message (plain text, with Outlook express for
example), the recipient sees a blank message with an attachment
containing the text.
If I comment (with an #) the new function action_rebuild() from
/etc/mail/mimedefang-filter, this behaviour goes away.

Follow my mimedefang-filter

# -*- Perl -*-
# mimedefang-filter

# This filter is "low risk" because it is very restrictive about what

# it allows through. Note that it DOES allow HTML attachments through,

# which may be a problem for your e-mail client.

#

# Copyright (C) 2000 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: low-risk-filter,v 1.17 2002/02/08 13:51:53 dfs Exp $

#***********************************************************************

#***********************************************************************

# Set administrator's name 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'

#***********************************************************************

$Administrator = 'postmaster at aive.it';

#***********************************************************************

# 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 = 'mailer-daemon at aive.it';

#***********************************************************************

# Set various stupid things your mail client does below.

#***********************************************************************

# Set the next one if your mail client cannot handle nested multipart

# messages

$Stupidity{"flatten"} = 0;

# Set the next one if your mail client cannot handle multiple "inline"

# parts (*cough* Exchange *cough* Outlook)

$Stupidity{"NoMultipleInlines"} = 1;

#***********************************************************************

# %PROCEDURE: filter_begin

# %ARGUMENTS:

# None

# %RETURNS:

# Nothing

# %DESCRIPTION:

# Called just before e-mail parts are processed

#***********************************************************************

#sub filter_begin {

# # Only if you have NAI virus scanner, use this. See the
mimedefang-filter

# # man page for other virus scanners.

# $VirusFound = message_contains_virus_nai();

#

# # Example: Only allow mailing to "all at mycorp.com" from our mail server

# $OurMailServer = 192.168.7.4;

# if ($RelayAddr ne $OurMailServer) {

# foreach $recip (@Recipients) {

# if ($recip eq 'all at mycorp.com') {

# action_bounce('Outsiders may not mail to all at mycorp.com');

# last;

# }

# }

# }

#}

#***********************************************************************

# %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_bounce("The message was rejected because of suspicious characters
in headers.");

#action_notify_administrator("Message quarantined because of suspicious
characters in headers");

# Do NOT allow message to reach recipient(s)

#action_discard();

}

# Outlook has MIME-parsing bugs. To prevent malformed messages from

# triggering them, always rebuild the message. CPU-intensive, but

# that's the price you pay for using Microsoft client software.

action_rebuild();

}

sub filter {

my($entity, $fname, $ext, $type) = @_;

# For convenience, compute lower-case versions of filename and extension

my($lc_fname) = $fname;

my($lc_ext) = $ext;

$lc_fname =~ tr/A-Z/a-z/;

$lc_ext =~ tr/A-Z/a-z/;

####################################################################

# #

# Filter rules follow #

# #

####################################################################

#-------------------------------------------------------------------

# Quarantine viruses

#-------------------------------------------------------------------

# Only if you have NAI virus scanner, use this. See the
mimedefang-filter

# man page for other virus scanners.

#if ($VirusFound && entity_contains_virus_nai($entity)) {

# # Notify the sender if you desire

# action_notify_sender("The attachment '$fname' was deleted. It
contains\n".

# "a known virus.\nHere is the output from the virus
scanner:\n$VirusScannerMessages");

#

# return action_quarantine($entity, "The attachment $fname contains a
known virus. It has been quarantined.\nHere is the output from the virus
scanner:\n$VirusScannerMessages");

#}

#-------------------------------------------------------------------

# Quarantine possible executables.

#-------------------------------------------------------------------


if (re_match_ext($entity,
'^\.(exe|com|bat|vbs|scr|shs|dll|vxd|pif|reg|ocx|lnk|js|ini|mdb|wpd|wk4|
eml)$')){

# Notify the sender if you desire

#action_notify_sender("The attachment '$fname' was deleted. We do
not\n".

# "accept attachments of type '$ext'.\n");

action_notify_sender("The message was deleted. We do not accept\n".

"message with attachments of type '$ext'.\n");

# Discard the message

return action_discard();

# Quarantine the attachment.

#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");

}

#-------------------------------------------------------------------

# Accept any kind of textual attachment

#-------------------------------------------------------------------

if ($type =~ m+^text/+) {

return action_accept();

}

# This type is generated by some buggy mail clients.

if ($type eq "text") {

return action_accept();

}

#-------------------------------------------------------------------

# Messages (generated by mail transfer agents)

#-------------------------------------------------------------------

if ($type =~
m+^message/(rfc822|partial|news|delivery-status|disposition-notification
)$+) {

return action_accept();

}

#-------------------------------------------------------------------

# Images with stringent filename checks

#-------------------------------------------------------------------

if (($type eq "image/jpeg" && ($lc_ext eq ".jpg" || $lc_ext eq ".jpeg"))
||

($type eq "image/gif" && $lc_ext eq ".gif") ||

($type eq "image/bmp" && $lc_ext eq ".bmp") ||

($type eq "image/png" && $lc_ext eq ".png") ||

($type eq "image/tiff" && ($lc_ext eq ".tif" || $lc_ext eq ".tiff"))) {

return action_accept();

}

#-------------------------------------------------------------------

# PDF's are OK if the filename is sane

#-------------------------------------------------------------------

if ($type eq "application/pdf" && $lc_ext eq ".pdf") {

return action_accept();

}

#-------------------------------------------------------------------

# ZIP's are OK. My boss also want xls, doc and ppt

#-------------------------------------------------------------------

if (re_match_ext($entity, '^\.(xls|doc|ppt|zip|gz|tgz|Z)$')){

return action_accept();

}

#-------------------------------------------------------------------

# Don't do double-defanging on things we recognize as safe

#-------------------------------------------------------------------

if ($type eq "application/octet-stream" && $fname =~
/^defang-\d+\.binary$/) {

return action_accept();

}

#-------------------------------------------------------------------

# Drop anything else

#-------------------------------------------------------------------

#return action_drop_with_warning("An attachment named $fname was removed
from this document as it\nis of unknown type and may constitute a
security hazard.\nIf you require this document, please contact\nthe
sender and arrange an alternate means of receiving it.\n");

return action_bounce("The message was rejected because it contains an
unknown attachment type.");

}



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";

}

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

1;