Subversion Repositories configs

# HEADER_CHECKS(5)                                              HEADER_CHECKS(5)

#

# NAME

#        header_checks - Postfix built-in content inspection

#

# SYNOPSIS

#        header_checks = pcre:/etc/postfix/header_checks

#        mime_header_checks = pcre:/etc/postfix/mime_header_checks

#        nested_header_checks = pcre:/etc/postfix/nested_header_checks

#        body_checks = pcre:/etc/postfix/body_checks

#

#        postmap -q "string" pcre:/etc/postfix/filename

#        postmap -q - pcre:/etc/postfix/filename <inputfile

#

# DESCRIPTION

#        This  document  describes access control on the content of

#        message headers and message body lines; it is  implemented

#        by  the  Postfix  cleanup(8) server before mail is queued.

#        See access(5) for access control  on  remote  SMTP  client

#        information.

#

#        Each  message  header  or  message  body  line is compared

#        against a list of patterns.  When a  match  is  found  the

#        corresponding action is executed, and the matching process

#        is repeated for the next message header  or  message  body

#        line.

#

#        For  examples, see the EXAMPLES section at the end of this

#        manual page.

#

#        Postfix header or body_checks are designed to stop a flood

#        of  mail from worms or viruses; they do not decode attach-

#        ments, and they do not unzip archives. See  the  documents

#        referenced  below  in the README FILES section if you need

#        more sophisticated content analysis.

#

#        Postfix supports four built-in content inspection classes:

#

#        header_checks

#               These   are  applied  to  initial  message  headers

#               (except for the headers  that  are  processed  with

#               mime_header_checks).

#

#        mime_header_checks (default: $header_checks)

#               These  are  applied to MIME related message headers

#               only.

#

#               This feature is available in Postfix 2.0 and later.

#

#        nested_header_checks (default: $header_checks)

#               These  are  applied  to message headers of attached

#               email messages (except for  the  headers  that  are

#               processed with mime_header_checks).

#

#               This feature is available in Postfix 2.0 and later.

#

#        body_checks

#               These are applied to all other  content,  including

#               multi-part message boundaries.

#

#               With Postfix versions before 2.0, all content after

#               the initial message headers is treated as body con-

#               tent.

#

#        Note: message headers are examined one logical header at a

#        time, even when a message  header  spans  multiple  lines.

#        Body lines are always examined one line at a time.

#

# COMPATIBILITY

#        With Postfix version 2.2 and earlier specify "postmap -fq"

#        to query a table that contains case sensitive patterns. By

#        default,  regexp: and pcre: patterns are case insensitive.

#

# TABLE FORMAT

#        This document assumes that header  and  body_checks  rules

#        are  specified  in  the form of Postfix regular expression

#        lookup tables. Usually the best  performance  is  obtained

#        with pcre (Perl Compatible Regular Expression) tables, but

#        the slower regexp (POSIX regular expressions)  support  is

#        more  widely  available.  Use the command "postconf -m" to

#        find out what lookup table types your Postfix system  sup-

#        ports.

#

#        The general format of Postfix regular expression tables is

#        given below.  For a  discussion  of  specific  pattern  or

#        flags   syntax,   see  pcre_table(5)  or  regexp_table(5),

#        respectively.

#

#        /pattern/flags action

#               When /pattern/ matches the  input  string,  execute

#               the  corresponding  action. See below for a list of

#               possible actions.

#

#        !/pattern/flags action

#               When /pattern/ does not  match  the  input  string,

#               execute the corresponding action.

#

#        if /pattern/flags

#

#        endif  Match the input string against the patterns between

#               if and endif, if and only if the same input  string

#               also matches /pattern/. The if..endif can nest.

#

#               Note:  do not prepend whitespace to patterns inside

#               if..endif.

#

#        if !/pattern/flags

#

#        endif  Match the input string against the patterns between

#               if  and endif, if and only if the same input string

#               does not match /pattern/. The if..endif can nest.

#

#        blank lines and comments

#               Empty lines and whitespace-only lines are  ignored,

#               as  are  lines whose first non-whitespace character

#               is a `#'.

#

#        multi-line text

#               A pattern/action line  starts  with  non-whitespace

#               text.  A line that starts with whitespace continues

#               a logical line.

#

# TABLE SEARCH ORDER

#        For each line of message input, the patterns  are  applied

#        in  the order as specified in the table. When a pattern is

#        found that  matches  the  input  line,  the  corresponding

#        action  is  executed  and  then  the  next  input  line is

#        inspected.

#

# TEXT SUBSTITUTION

#        Substitution of substrings  from  the  matched  expression

#        into  the action string is possible using the conventional

#        Perl syntax ($1, $2, etc.).   The  macros  in  the  result

#        string  may  need  to  be  written as ${n} or $(n) if they

#        aren't followed by whitespace.

#

#        Note: since negated patterns (those preceded by !)  return

#        a result when the expression does not match, substitutions

#        are not available for negated patterns.

#

# ACTIONS

#        Action names are case insensitive. They are shown in upper

#        case for consistency with other Postfix documentation.

#

#        DISCARD optional text...

#               Claim  successful delivery and silently discard the

#               message.  Log the optional text if specified,  oth-

#               erwise log a generic message.

#

#               Note:   this  action  disables  further  header  or

#               body_checks inspection of the current  message  and

#               affects all recipients.  To discard only one recip-

#               ient without discarding the entire message, use the

#               transport(5) table to direct mail to the discard(8)

#               service.

#

#               This feature is available in Postfix 2.0 and later.

#

#        DUNNO  Pretend  that the input line did not match any pat-

#               tern, and inspect the next input line. This  action

#               can be used to shorten the table search.

#

#               For  backwards  compatibility reasons, Postfix also

#               accepts OK but it is (and always has been)  treated

#               as DUNNO.

#

#               This feature is available in Postfix 2.1 and later.

#

#        FILTER transport:destination

#               Write a content filter request to the  queue  file,

#               and  inspect  the  next input line.  After the com-

#               plete message is received it will be  sent  through

#               the specified external content filter.  More infor-

#               mation about external content  filters  is  in  the

#               Postfix FILTER_README file.

#

#               Note: this action overrides the content_filter set-

#               ting, and affects all recipients of the message. In

#               the  case  that  multiple FILTER actions fire, only

#               the last one is executed.

#

#               This feature is available in Postfix 2.0 and later.

#

#        HOLD optional text...

#               Arrange  for  the  message to be placed on the hold

#               queue, and inspect the next input line.   The  mes-

#               sage  remains  on hold until someone either deletes

#               it or releases it for delivery.  Log  the  optional

#               text if specified, otherwise log a generic message.

#

#               Mail that is placed on hold can  be  examined  with

#               the  postcat(1)  command,  and  can be destroyed or

#               released with the postsuper(1) command.

#

#               Note: use "postsuper -r" to release mail  that  was

#               kept  on  hold for a significant fraction of $maxi-

#               mal_queue_lifetime  or  $bounce_queue_lifetime,  or

#               longer.  Use "postsuper -H" only for mail that will

#               not expire within a few delivery attempts.

#

#               Note: this action affects  all  recipients  of  the

#               message.

#

#               This feature is available in Postfix 2.0 and later.

#

#        IGNORE Delete the current line from the input, and inspect

#               the next input line.

#

#        PREPEND text...

#               Prepend  one  line  with  the  specified  text, and

#               inspect the next input line.

#

#               Notes:

#

#               o      The prepended text is output on  a  separate

#                      line,  immediately  before  the  input  that

#                      triggered the PREPEND action.

#

#               o      The prepended text is not considered part of

#                      the  input  stream:  it  is  not  subject to

#                      header/body checks or address rewriting, and

#                      it does not affect the way that Postfix adds

#                      missing message headers.

#

#               o      When prepending text before a message header

#                      line,  the  prepended text must begin with a

#                      valid message header label.

#

#               o      This action cannot be used to prepend multi-

#                      line text.

#

#               This feature is available in Postfix 2.1 and later.

#

#        REDIRECT user@domain

#               Write a message redirection request  to  the  queue

#               file,  and  inspect  the next input line. After the

#               message is queued, it will be sent to the specified

#               address instead of the intended recipient(s).

#

#               Note:  this action overrides the FILTER action, and

#               affects all recipients of the message. If  multiple

#               REDIRECT  actions  fire,  only the last one is exe-

#               cuted.

#

#               This feature is available in Postfix 2.1 and later.

#

#        REPLACE text...

#               Replace  the  current line with the specified text,

#               and inspect the next input line.

#

#               This feature is available in Postfix 2.2 and later.

#               The  description below applies to Postfix 2.2.2 and

#               later.

#

#               Notes:

#

#               o      When replacing a message  header  line,  the

#                      replacement  text  must  begin  with a valid

#                      header label.

#

#               o      The replaced text remains part of the  input

#                      stream.  Unlike  the result from the PREPEND

#                      action, a replaced  message  header  may  be

#                      subject  to address rewriting and may affect

#                      the way that Postfix  adds  missing  message

#                      headers.

#

#        REJECT optional text...

#               Reject  the  entire  message.  Reply  with optional

#               text... when the optional text is specified, other-

#               wise reply with a generic error message.

#

#               Note:   this  action  disables  further  header  or

#               body_checks inspection of the current  message  and

#               affects all recipients.

#

#               Postfix version 2.3 and later support enhanced sta-

#               tus codes.  When no code is specified at the begin-

#               ning of optional text..., Postfix inserts a default

#               enhanced status code of "5.7.1".

#

#        WARN optional text...

#               Log a warning with the optional text... (or  log  a

#               generic  message), and inspect the next input line.

#               This action is useful for debugging and for testing

#               a pattern before applying more drastic actions.

#

# BUGS

#        Empty lines never match, because some map types mis-behave

#        when given a zero-length search string.   This  limitation

#        may  be  removed for regular expression tables in a future

#        release.

#

#        Many people overlook the main limitations  of  header  and

#        body_checks rules.

#

#        o      These  rules  operate on one logical message header

#               or one body line at a time. A decision made for one

#               line is not carried over to the next line.

#

#        o      If  text  in the message body is encoded (RFC 2045)

#               then the rules need to be specified for the encoded

#               form.

#

#        o      Likewise,  when  message  headers  are encoded (RFC

#               2047) then the rules need to be specified  for  the

#               encoded form.

#

#        Message  headers added by the cleanup(8) daemon itself are

#        excluded from inspection. Examples of such message headers

#        are From:, To:, Message-ID:, Date:.

#

#        Message  headers  deleted by the cleanup(8) daemon will be

#        examined before they are deleted. Examples are: Bcc:, Con-

#        tent-Length:, Return-Path:.

#

# CONFIGURATION PARAMETERS

#        body_checks

#               Lookup tables with content filter rules for message

#               body lines.  These filters see one physical line at

#               a  time,  in  chunks  of at most $line_length_limit

#               bytes.

#

#        body_checks_size_limit

#               The amount of  content  per  message  body  segment

#               (attachment) that is subjected to $body_checks fil-

#               tering.

#

#        header_checks

#

#        mime_header_checks (default: $header_checks)

#

#        nested_header_checks (default: $header_checks)

#               Lookup tables with content filter rules for message

#               header  lines:  respectively,  these are applied to

#               the initial message  headers  (not  including  MIME

#               headers),  to the MIME headers anywhere in the mes-

#               sage, and to the initial headers of  attached  mes-

#               sages.

#

#               Note:  these filters see one logical message header

#               at a time, even when a message header spans  multi-

#               ple  lines.  Message  headers  that are longer than

#               $header_size_limit characters are truncated.

#

#        disable_mime_input_processing

#               While receiving mail, give no special treatment  to

#               MIME  related  message  headers; all text after the

#               initial message headers is considered to be part of

#               the  message body. This means that header_checks is

#               applied to all the  initial  message  headers,  and

#               that body_checks is applied to the remainder of the

#               message.

#

#               Note: when used in this  manner,  body_checks  will

#               process  a  multi-line message header one line at a

#               time.

#

# EXAMPLES

#        Header pattern to block attachments  with  bad  file  name

#        extensions.   For  convenience, the PCRE /x flag is speci-

#        fied, so that there is no need  to  collapse  the  pattern

#        into   a   single  line  of  text.   The  purpose  of  the

#        [[:xdigit:]] sub-expressions is to recognize Windows CLSID

#        strings.

#

#        /etc/postfix/main.cf:

#            header_checks = pcre:/etc/postfix/header_checks.pcre

#

#        /etc/postfix/header_checks.pcre:

#            /^Content-(Disposition|Type).*name\s*=\s*"?(.*(\.|=2E)(

#              ade|adp|asp|bas|bat|chm|cmd|com|cpl|crt|dll|exe|

#              hlp|ht[at]|

#              inf|ins|isp|jse?|lnk|md[betw]|ms[cipt]|nws|

#              \{[[:xdigit:]]{8}(?:-[[:xdigit:]]{4}){3}-[[:xdigit:]]{12}\}|

#              ops|pcd|pif|prf|reg|sc[frt]|sh[bsm]|swf|

#              vb[esx]?|vxd|ws[cfh]))(\?=)?"?\s*(;|$)/x

#                REJECT Attachment name "$2" may not end with ".$4"

#

#        Body pattern to stop a specific HTML browser vulnerability

#        exploit.

#

#        /etc/postfix/main.cf:

#            body_checks = regexp:/etc/postfix/body_checks

#

#        /etc/postfix/body_checks:

#            /^<iframe src=(3D)?cid:.* height=(3D)?0 width=(3D)?0>$/

#                REJECT IFRAME vulnerability exploit

#

# SEE ALSO

#        cleanup(8), canonicalize and enqueue Postfix message

#        pcre_table(5), format of PCRE lookup tables

#        regexp_table(5), format of POSIX regular expression tables

#        postconf(1), Postfix configuration utility

#        postmap(1), Postfix lookup table management

#        postsuper(1), Postfix janitor

#        postcat(1), show Postfix queue file contents

#        RFC 2045, base64 and quoted-printable encoding rules

#        RFC 2047, message header encoding for non-ASCII text

#

# README FILES

#        Use "postconf readme_directory" or  "postconf  html_direc-

#        tory" to locate this information.

#        DATABASE_README, Postfix lookup table overview

#        CONTENT_INSPECTION_README, Postfix content inspection overview

#        BUILTIN_FILTER_README, Postfix built-in content inspection

#        BACKSCATTER_README, blocking returned forged mail

#

# LICENSE

#        The  Secure  Mailer  license must be distributed with this

#        software.

#

# AUTHOR(S)

#        Wietse Venema

#        IBM T.J. Watson Research

#        P.O. Box 704

#        Yorktown Heights, NY 10598, USA

#

#                                                               HEADER_CHECKS(5)