/etc/system_filter.exim

# Exim filter
#VERSION=1.3
## Version: 0.17e
#	$Id: system_filter.exim,v 1.11 2001/09/19 11:27:56 nigel Exp $

## Exim system filter to refuse potentially harmful payloads in
## mail messages
## (c) 2000-2001 Nigel Metheringham <[email protected]>
##
##     This program is free software; you can redistribute it and/or modify
##    it under the terms of the GNU General Public License as published by
##    the Free Software Foundation; either version 2 of the License, or
##    (at your option) any later version.
##
##    This program is distributed in the hope that it will be useful,
##    but WITHOUT ANY WARRANTY; without even the implied warranty of
##    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
##    GNU General Public License for more details.
##
##    You should have received a copy of the GNU General Public License
##    along with this program; if not, write to the Free Software
##    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
## -A copy of the GNU General Public License is distributed with exim itself

## -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
## If you haven't worked with exim filters before, read
## the install notes at the end of this file.
## The install notes are not a replacement for the exim documentation
## -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-


## -----------------------------------------------------------------------
# Only run any of this stuff on the first pass through the
# filter - this is an optomisation for messages that get
# queued and have several delivery attempts
#
# we express this in reverse so we can just bail out
# on inappropriate messages
#
if not first_delivery
then
  finish
endif

## -----------------------------------------------------------------------
# Check for MS buffer overruns as per BUGTRAQ.
# http://www.securityfocus.com/frames/?content=/templates/article.html%3Fid%3D61
# This could happen in error messages, hence its placing
# here...
# We substract the first n characters of the date header
# and test if its the same as the date header... which
# is a lousy way of checking if the date is longer than
# n chars long
if ${length_80:$header_date:} is not $header_date:
then
  seen finish
endif

## -----------------------------------------------------------------------
# These messages are now being sent with a <> envelope sender, but
# blocking all error messages that pattern match prevents
# bounces getting back.... so we fudge it somewhat and check for known
# header signatures.  Other bounces are allowed through.
if $header_from: contains "@sexyfun.net"
then
  seen finish
endif
if error_message and $header_from: contains "Mailer-Daemon@"
then
  # looks like a real error message - just ignore it
  finish
endif

## -----------------------------------------------------------------------
# Look for single part MIME messages with suspicious name extensions
# Check Content-Type header using quoted filename [content_type_quoted_fn_match]
if $header_content-type: matches "(?:file)?name=\"([^\"]+\\\\.(?:ad[ep]|ba[st]|chm|cmd|com|cpl|crt|eml|exe|hlp|hta|in[fs]|isp|jse?|lnk|md[be]|ms[cipt]|pcd|pif|reg|sc[mrt]|shs|url|vb[se]?|ws[fhc]))\""
then
  seen finish
endif
# same again using unquoted filename [content_type_unquoted_fn_match]
if $header_content-type: matches "(?:file)?name=(\\\\S+\\\\.(?:ad[ep]|ba[st]|chm|cmd|com|cpl|crt|eml|exe|hlp|hta|in[fs]|isp|jse?|lnk|md[be]|ms[cipt]|pcd|pif|reg|sc[mrt]|shs|url|vb[se]?|ws[fhc])\")([\\\\s;]|\\$)"
then
  seen finish
endif


## -----------------------------------------------------------------------
# Attempt to catch embedded VBS attachments
# in emails.   These were used as the basis for
# the ILOVEYOU virus and its variants - many many varients
# Quoted filename - [body_quoted_fn_match]
if $message_body matches "(?:Content-(?:Type:(?>\\\\s*)[\\\\w-]+/[\\\\w-]+|Disposition:(?>\\\\s*)attachment);(?>\\\\s*)(?:file)?name=|begin(?>\\\\s+)[0-7]{3,4}(?>\\\\s+))\"([^\"]+\\\\.(?:ad[ep]|ba[st]|chm|cmd|com|cpl|crt|eml|exe|hlp|hta|in[fs]|isp|jse?|lnk|md[be]|ms[cipt]|pcd|pif|reg|sc[mrt]|shs|url|vb[se]?|ws[fhc])\")[\\\\s;]"
then
  seen finish
endif
# same again using unquoted filename [body_unquoted_fn_match]
if $message_body matches "(?:Content-(?:Type:(?>\\\\s*)[\\\\w-]+/[\\\\w-]+|Disposition:(?>\\\\s*)attachment);(?>\\\\s*)(?:file)?name=|begin(?>\\\\s+)[0-7]{3,4}(?>\\\\s+))(\\\\S+\\\\.(?:ad[ep]|ba[st]|chm|cmd|com|cpl|crt|eml|exe|hlp|hta|in[fs]|isp|jse?|lnk|md[be]|ms[cipt]|pcd|pif|reg|sc[mrt]|shs|url|vb[se]?|ws[fhc])\")[\\\\s;]"
then
  seen finish
endif
## -----------------------------------------------------------------------

# Fudge to catch Klez virus (mal formed mime details, unquoted filename with spaces)
#if $message_body matches "Content-Type:(?>\\\\s*)[\\\\w-]+/[\\\\w-]+;\\\\s*(?:name)=([^\" ]+ [^\"]*\\\\.(?:ad[ep]|ba[st]|chm|cmd|com|cpl|crt|eml|exe|hlp|hta|in[fs]|isp|jse?|lnk|md[be]|ms[cipt]|pcd|pif|reg|sc[mrt]|shs|url|vb[se]?|ws[fhc])\")[\\\\s;]"
#then
#  seen finish
#endif


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


#### Version history
#
# 0.01 5 May 2000
#	Initial release
# 0.02 8 May 2000
#	Widened list of content-types accepted, added WSF extension
# 0.03 8 May 2000
#	Embedded the install notes in for those that don't do manuals
# 0.04 9 May 2000
#	Check global content-type header.  Efficiency mods to REs
# 0.05 9 May 2000
#	More minor efficiency mods, doc changes
# 0.06 20 June 2000
#	Added extension handling - thx to Douglas Gray Stephens & Jeff Carnahan
# 0.07 19 July 2000
#	Latest MS Outhouse bug catching
# 0.08 19 July 2000
#	Changed trigger length to 80 chars, fixed some spelling
# 0.09 29 September 2000
#	More extensions... its getting so we should just allow 2 or 3 through
# 0.10 18 January 2001
#	Removed exclusion for error messages - this is a little nasty
#	since it has other side effects, hence we do still exclude
#	on unix like error messages
# 0.11 20 March, 2001
#	Added CMD extension, tidied docs slightly, added RCS tag
#	** Missed changing version number at top of file :-(
# 0.12 10 May, 2001
#	Added HTA extension
# 0.13 22 May, 2001
#	Reformatted regexps and code to build them so that they are
#	shorter than the limits on pre exim 3.20 filters.  This will
#	make them significantly less efficient, but I am getting so
#	many queries about this that requiring 3.2x appears unsupportable.
# 0.14 15 August,2001
#	Added .lnk extension - most requested item :-)
#	Reformatted everything so its now built from a set of short
#	library files, cutting down on manual duplication.
#	Changed \w in filename detection to . - dodges locale problems
#	Explicit application of GPL after queries on license status
# 0.15 17 August, 2001
#	Changed the . in filename detect to \S (stops it going mad)
# 0.16 19 September, 2001
#	Pile of new extensions including the eml in current use
# 0.17 19 September, 2001
#	Syntax fix
# 0.17a Thu 21-Feb-2002; Douglas Gray Stephens
#        Modify for SLB (adding null return path test)
# 0.17b Wed 01-May-2002; Douglas Gray Stephens
#        Block mal formed mime messages that have a space in the name
# 0.17c Wed 15-May-2002; Douglas Gray Stephens
#        Block mal formed mime messages that have a space and period
#        in the name.
#	 Also block .vb extensions
# 0.17d Thu 16-May-2002; Douglas Gray Stephens
#        Update the notes as Exim 4 uses system_filter_* rather
#        than message_filter_*
#        (after feedback from  David Broome <[email protected]>)
# 0.17e Fri 19-Jul-2002; Douglas Gray Stephens
#        Block SCM (ScreenCam Movie) files
# 1.2	13-Apr-2018 Removed the Klez check as it was breaking:
#	 Content-Type: multipart/report;\n...
#	 from RoundCube emails.


#
#### Install Notes
#
# Exim filters run the exim filter language - a very primitive
# scripting language - in place of a user .forward file, or on
# a per system basis (on all messages passing through).
# The filtering capability is documented in the main set of manuals
# a copy of which can be found on the exim web site
#	http://www.exim.org/
#
# To install, copy the filter file (with appropriate permissions)
# to /etc/exim/system_filter.exim and add to your exim config file
# [location is installation depedant - typicaly /etc/exim/config ]
# in the first section the line:-
#   Exim 3
#	message_filter = /etc/exim/system_filter.exim
#	message_body_visible = 5000
#   Exim 4
#	system_filter = /etc/exim/system_filter.exim
#	message_body_visible = 5000
#
# You may also want to set the message_filter_user & message_filter_group
# (in Exim 4 these are system_filter_user & system_filter_group)
# options, but they default to the standard exim user and so can
# be left untouched.  The other message_filter_* (or system_filter_*
# for Exim 4) options are only needed if you modify this to do other
# functions such as deliveries.
# The main exim documentation is quite thorough and so I see no need
# to expand it here...
#
# Any message that matches the filter will then be bounced.
# If you wish you can change the error message by editing it
# in the section above - however be careful you don't break it.
#
# After install exim should be restarted - a kill -HUP to the
# daemon will do this.
#
#### LIMITATIONS
#
# This filter tries to parse MIME with a regexp... that doesn't
# work too well.  It will also only see the amount of the body
# specified in message_body_visible
#
#### BASIS
#
# The regexp that is used to pickup MIME/uuencoded body parts with
# quoted filenames is replicated below (in perl format).
# You need to remember that exim converts newlines to spaces in
# the message_body variable.
#
#	  (?:Content-					# start of content header
#	  (?:Type: (?>\s*)				# rest of c/t header
#	    [\w-]+/[\w-]+				# content-type (any)
#	    |Disposition: (?>\s*)			# content-disposition hdr
#	    attachment)					# content-disposition
#	  ;(?>\s*)					# ; space or newline
#	  (?:file)?name=				# filename=/name=
#	  |begin (?>\s+) [0-7]{3,4} (?>\s+)) 		# begin octal-mode
#	  (\"[^\"]+\.					# quoted filename.
#		(?:ad[ep]				# list of extns
#		|ba[st]
#		|chm
#		|cmd
#		|com
#		|cpl
#		|crt
#		|eml
#		|exe
#		|hlp
#		|hta
#		|in[fs]
#		|isp
#		|jse?
#		|lnk
#		|md[be]
#		|ms[cipt]
#		|pcd
#		|pif
#		|reg
#		|scm
#		|scr
#		|sct
#		|shs
#		|url
#		|vb[se]?
#		|ws[fhc])
#	  \"						# end quote
#	  )						# end of filename capture
#	  [\s;]						# trailing ;/space/newline

#
#
### [End]