fixed FAQ

[exim-website.git] / system_filter.exim

diff --git a/system_filter.exim b/system_filter.exim
index abbd0236f3444ba7c96c1cad69332468b784636b..e91a88020f5ba66ec17b67f3f2ba17c7ac1dd123 100644 (file)
--- a/system_filter.exim
+++ b/system_filter.exim
@@ -1,10 +1,34 @@
 # Exim filter
 # Exim filter

-## Version: 0.10
+## Version: 0.17
+#      $Id: sysfilter.tmpl,v 1.4 2001/09/19 10:19:42 nigel Exp $

 
 

+## Exim system filter to refuse potentially harmful payloads in
+## mail messages
+## (c) 2000-2001 Nigel Metheringham <nigel@exim.org>
+##
+##     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.
 ## 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
 # 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


@@ -17,7 +41,8 @@ then
   finish
 endif
 
   finish
 endif
 

-# Check for MS buffer overruns as per latest BUGTRAQ.
+## -----------------------------------------------------------------------
+# 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...
 # http://www.securityfocus.com/frames/?content=/templates/article.html%3Fid%3D61
 # This could happen in error messages, hence its placing
 # here...


@@ -28,21 +53,22 @@ endif
 if ${length_80:$header_date:} is not $header_date:
 then
   fail text "This message has been rejected because it has\n\
 if ${length_80:$header_date:} is not $header_date:
 then
   fail text "This message has been rejected because it has\n\

-            \tan overlength date field which can be used\n\
-            \tto subvert Microsoft mail programs\n\
-             \tThe following URL has further information\n\
-            \thttp://www.securityfocus.com/frames/?content=/templates/article.html%3Fid%3D61"
+            an overlength date field which can be used\n\
+            to subvert Microsoft mail programs\n\
+             The following URL has further information\n\
+            http://www.securityfocus.com/frames/?content=/templates/article.html%3Fid%3D61"

   seen finish
 endif
 
   seen finish
 endif
 

-# This is a nasty compromise.
-# This crud is now being sent with a <> envelope sender, but
+## -----------------------------------------------------------------------
+# These messages are now being sent with a <> envelope sender, but

 # blocking all error messages that pattern match prevents
 # blocking all error messages that pattern match prevents

-# bounces getting back.... so we fudge it somewhat
+# 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
   fail text "This message has been rejected since it has\n\
 if $header_from: contains "@sexyfun.net"
 then
   fail text "This message has been rejected since it has\n\

-               \tthe signature of a known virus in the header."
+            the signature of a known virus in the header."

   seen finish
 endif
 if error_message and $header_from: contains "Mailer-Daemon@"
   seen finish
 endif
 if error_message and $header_from: contains "Mailer-Daemon@"


@@ -51,35 +77,60 @@ then
   finish
 endif
 
   finish
 endif
 

+## -----------------------------------------------------------------------

 # Look for single part MIME messages with suspicious name extensions
 # Look for single part MIME messages with suspicious name extensions

-# Check Content-Type header [vb2_regexp]
-if $header_content-type: matches "(?:file)?name=(\"[^\"]+\\\\.(?:vb[se]|ws[fh]|jse?|exe|com|shs|bat|scr|pif)\"|[\\\\w.-]+\\\\.(?:vb[se]|ws[fh]|jse?|exe|com|shs|bat|scr|pif))"
+# 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|scr|sct|shs|url|vb[se]|ws[fhc])\")"
+then
+  fail text "This message has been rejected because it has\n\
+            potentially executable content $1\n\
+            This form of attachment has been used by\n\
+             recent viruses or other malware.\n\
+            If you meant to send this file then please\n\
+            package it up as a zip file and resend it."
+  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|scr|sct|shs|url|vb[se]|ws[fhc]))"

 then
   fail text "This message has been rejected because it has\n\
 then
   fail text "This message has been rejected because it has\n\

-            \ta potentially executable attachment $1\n\
-            \tThis form of attachment has been used by\n\
-             \trecent viruses such as that described in\n\
-            \thttp://www.fsecure.com/v-descs/love.htm\n\
-            \tIf you meant to send this file then please\n\
-            \tpackage it up as a zip file and resend it."
+            potentially executable content $1\n\
+            This form of attachment has been used by\n\
+             recent viruses or other malware.\n\
+            If you meant to send this file then please\n\
+            package it up as a zip file and resend it."

   seen finish
 endif
 
   seen finish
 endif
 

+
+## -----------------------------------------------------------------------

 # Attempt to catch embedded VBS attachments
 # in emails.   These were used as the basis for 
 # Attempt to catch embedded VBS attachments
 # in emails.   These were used as the basis for 

-# the ILOVEYOU virus and its variants
-# [vb_regexp]
-if $message_body matches "(?:Content-(?:Type:(?>\\\\s*)[\\\\w-]+/[\\\\w-]+|Disposition:(?>\\\\s*)attachment);(?>\\\\s*)(?:file)?name=|begin(?>\\\\s+)[0-7]{3,4}(?>\\\\s+))(\"[^\"]+\\\\.(?:vb[se]|ws[fh]|jse?|exe|com|shs|bat|scr|pif)\"|[\\\\w.-]+\\\\.(?:vb[se]|ws[fh]|jse?|exe|com|shs|bat|scr|pif))[\\\\s;]"
+# 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|scr|sct|shs|url|vb[se]|ws[fhc])\")[\\\\s;]"

 then
   fail text "This message has been rejected because it has\n\
 then
   fail text "This message has been rejected because it has\n\

-            \ta potentially executable attachment $1\n\
-            \tThis form of attachment has been used by\n\
-             \trecent viruses such as that described in\n\
-            \thttp://www.fsecure.com/v-descs/love.htm\n\
-            \tIf you meant to send this file then please\n\
-            \tpackage it up as a zip file and resend it."
+            a potentially executable attachment $1\n\
+            This form of attachment has been used by\n\
+             recent viruses or other malware.\n\
+            If you meant to send this file then please\n\
+            package it up as a zip file and resend it."

   seen finish
 endif
   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|scr|sct|shs|url|vb[se]|ws[fhc]))[\\\\s;]"
+then
+  fail text "This message has been rejected because it has\n\
+            a potentially executable attachment $1\n\
+            This form of attachment has been used by\n\
+             recent viruses or other malware.\n\
+            If you meant to send this file then please\n\
+            package it up as a zip file and resend it."
+  seen finish
+endif
+## -----------------------------------------------------------------------
+

 
 #### Version history
 #
 
 #### Version history
 #


@@ -105,6 +156,28 @@ endif
 #      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
 #      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

 #
 #### Install Notes
 #
 #
 #### Install Notes
 #


@@ -118,10 +191,17 @@ endif
 # 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 ]
 # 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 ]

-# at the top the line:-
+# in the first section the line:-

 #      message_filter = /etc/exim/system_filter.exim
 #      message_body_visible = 5000
 #
 #      message_filter = /etc/exim/system_filter.exim
 #      message_body_visible = 5000
 #

+# You may also want to set the message_filter_user & message_filter_group
+# options, but they default to the standard exim user and so can
+# be left untouched.  The other message_filter_* 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.
 # 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.


@@ -137,41 +217,50 @@ endif
 #
 #### BASIS
 #
 #
 #### BASIS
 #

-# The regexp that is used to pickup MIME/uuencoded parts 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.
-#      (?:vb[se]                               # list of extns
-#      |ws[fh]
-#      |jse?
-#      |exe
-#      |com
-#      |shs
-#      |bat
-#      |scr
-#      |pif)
-#      \"                                      # end quote
-#  |[\w.-]+\.                                  # unquoted filename.ext
-#      (?:vb[se]                               # list of extns
-#      |ws[fh]
-#      |jse?
-#      |exe
-#      |com
-#      |shs
-#      |bat
-#      |scr
-#      |pif)
-#  )                                           # end of filename capture
-#  [\s;]                                       # trailing ;/space/newline
+# 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
+#              |scr
+#              |sct
+#              |shs
+#              |url
+#              |vb[se]
+#              |ws[fhc])
+#        \"                                            # end quote
+#        )                                             # end of filename capture
+#        [\s;]                                         # trailing ;/space/newline
+

 #
 #
 ### [End]
 #
 #
 ### [End]