From b5896ba9f6047e7031e2bdee0622d543e11a6734 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 03:46:30 +0200 Subject: Adding upstream version 3.4.23. Signed-off-by: Daniel Baumann --- html/header_checks.5.html | 489 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 489 insertions(+) create mode 100644 html/header_checks.5.html (limited to 'html/header_checks.5.html') diff --git a/html/header_checks.5.html b/html/header_checks.5.html new file mode 100644 index 0000000..caf15b5 --- /dev/null +++ b/html/header_checks.5.html @@ -0,0 +1,489 @@ + + + + Postfix manual - header_checks(5) + 
+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
+
+       milter_header_checks = pcre:/etc/postfix/milter_header_checks
+
+       smtp_header_checks = pcre:/etc/postfix/smtp_header_checks
+       smtp_mime_header_checks = pcre:/etc/postfix/smtp_mime_header_checks
+       smtp_nested_header_checks = pcre:/etc/postfix/smtp_nested_header_checks
+       smtp_body_checks = pcre:/etc/postfix/smtp_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 head-
+       ers 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.
+
+       Note:  message  headers are examined one logical header at a time, even
+       when a message header spans multiple lines. Body lines are always exam-
+       ined one line at a time.
+
+       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 attachments, and they do not unzip
+       archives. See the documents referenced below in the README  FILES  sec-
+       tion if you need more sophisticated content analysis.
+
+FILTERS WHILE RECEIVING MAIL
+       Postfix  implements  the  following  four  built-in  content inspection
+       classes while receiving mail:
+
+       header_checks (default: empty)
+              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 content.
+
+FILTERS AFTER RECEIVING MAIL
+       Postfix  supports  a  subset of the built-in content inspection classes
+       after the message is received:
+
+       milter_header_checks (default: empty)
+              These are applied to headers that are added with Milter applica-
+              tions.
+
+              This feature is available in Postfix 2.7 and later.
+
+FILTERS WHILE DELIVERING MAIL
+       Postfix  supports  all four content inspection classes while delivering
+       mail via SMTP.
+
+       smtp_header_checks (default: empty)
+
+       smtp_mime_header_checks (default: empty)
+
+       smtp_nested_header_checks (default: empty)
+
+       smtp_body_checks (default: empty)
+              These features are available in Postfix 2.5 and later.
+
+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 Expres-
+       sion) tables. The regexp (POSIX regular expressions) tables are usually
+       slower, but more widely available.  Use the command  "postconf  -m"  to
+       find out what lookup table types your Postfix system supports.
+
+       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 correspond-
+              ing action. See below for a list of possible actions.
+
+       !/pattern/flags action
+              When /pattern/ does not match the input string, execute the cor-
+              responding action.
+
+       if /pattern/flags
+
+       endif  If  the  input  string  matches /pattern/, then match that input
+              string against the patterns between if and endif.  The if..endif
+              can nest.
+
+              Note: do not prepend whitespace to patterns inside if..endif.
+
+       if !/pattern/flags
+
+       endif  If  the  input  string does not match /pattern/, then match that
+              input string against the patterns  between  if  and  endif.  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.
+
+       BCC user@domain
+              Add the specified address as a BCC recipient,  and  inspect  the
+              next  input  line. The address must have a local part and domain
+              part. The number of BCC addresses that can be added  is  limited
+              only by the amount of available storage space.
+
+              Note  1:  the  BCC  address is added as if it was specified with
+              NOTIFY=NONE. The sender  will  not  be  notified  when  the  BCC
+              address  is  undeliverable,  as long as all down-stream software
+              implements RFC 3461.
+
+              Note 2: this ignores duplicate addresses (with the same delivery
+              status notification options).
+
+              This feature is available in Postfix 3.0 and later.
+
+              This feature is not supported with smtp header/body checks.
+
+       DISCARD optional text...
+              Claim  successful delivery and silently discard the message.  Do
+              not inspect  the  remainder  of  the  input  message.   Log  the
+              optional text if specified, otherwise log a generic message.
+
+              Note: this action disables further header or body_checks inspec-
+              tion of the current message and affects all recipients.  To dis-
+              card  only  one recipient without discarding the entire message,
+              use the transport(5) table to direct mail to the discard(8) ser-
+              vice.
+
+              This feature is available in Postfix 2.0 and later.
+
+              This feature is not supported with smtp header/body checks.
+
+       DUNNO  Pretend  that  the  input  line  did  not match any pattern, 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
+              Override the content_filter parameter setting, and  inspect  the
+              next  input  line.  After the message is queued, send the entire
+              message through  the  specified  external  content  filter.  The
+              transport  name  specifies  the  first  field of a mail delivery
+              agent definition in master.cf; the syntax of the next-hop desti-
+              nation  is  described  in  the  manual page of the corresponding
+              delivery agent.  More information about external content filters
+              is in the Postfix FILTER_README file.
+
+              Note  1: do not use $number regular expression substitutions for
+              transport or destination unless you know  that  the  information
+              has a trusted origin.
+
+              Note  2:  this  action overrides the main.cf content_filter set-
+              ting, and affects all recipients of the  message.  In  the  case
+              that  multiple  FILTER  actions  fire, only the last one is exe-
+              cuted.
+
+              Note 3: the purpose of the FILTER command is to override message
+              routing.   To  override  the  recipient's  transport but not the
+              next-hop destination, specify an empty filter destination (Post-
+              fix  2.7  and  later),  or  specify a transport:destination that
+              delivers through a different Postfix instance (Postfix  2.6  and
+              earlier). Other options are using the recipient-dependent trans-
+              port_maps  or  the  sender-dependent   sender_dependent_default-
+              _transport_maps features.
+
+              This feature is available in Postfix 2.0 and later.
+
+              This feature is not supported with smtp header/body checks.
+
+       HOLD optional text...
+              Arrange  for  the  message  to  be placed on the hold queue, and
+              inspect the next input line.  The message 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  $maximal_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.
+
+              This feature is not supported with smtp header/body checks.
+
+       IGNORE Delete  the  current  line  from the input, and inspect the next
+              input line. See STRIP for an alternative that logs the action.
+
+       INFO optional text...
+              Log an "info:" record  with  the  optional  text...  (or  log  a
+              generic  text),  and inspect the next input line. This action is
+              useful for routine logging or for debugging.
+
+              This feature is available in Postfix 2.8 and later.
+
+       PASS optional text...
+              Log a "pass:" record with the optional text... (or log a generic
+              text),  and turn off header, body, and Milter inspection for the
+              remainder of this message.
+
+              Note: this feature relies on trust in information that  is  easy
+              to forge.
+
+              This feature is available in Postfix 3.2 and later.
+
+              This feature is not supported with smtp header/body checks.
+
+       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,  immedi-
+                     ately 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.
+
+              This feature is not supported with milter_header_checks.
+
+       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 executed.
+
+              This feature is available in Postfix 2.1 and later.
+
+              This feature is not supported with smtp header/body checks.
+
+       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 descrip-
+              tion 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. Do not inspect the remainder of the
+              input message.  Reply with optional text...  when  the  optional
+              text is specified, otherwise reply with a generic error message.
+
+              Note: this action disables further header or body_checks inspec-
+              tion of the current message and affects all recipients.
+
+              Postfix  version  2.3  and  later support enhanced status codes.
+              When no code is specified at the beginning of optional  text...,
+              Postfix inserts a default enhanced status code of "5.7.1".
+
+              This feature is not supported with smtp header/body checks.
+
+       STRIP optional text...
+              Log  a  "strip:"  record  with  the  optional  text... (or log a
+              generic text), delete the input line from the input, and inspect
+              the next input line. See IGNORE for a silent alternative.
+
+              This feature is available in Postfix 3.2 and later.
+
+       WARN optional text...
+              Log  a  "warning:"  record  with  the optional text... (or log a
+              generic text), 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:,  Mes-
+       sage-ID:, Date:.
+
+       Message  headers  deleted  by  the  cleanup(8)  daemon will be examined
+       before  they  are  deleted.  Examples   are:   Bcc:,   Content-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 filtering.
+
+       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  any-
+              where  in  the  message,  and to the initial headers of attached
+              messages.
+
+              Note: these filters see one logical message header  at  a  time,
+              even when a message header spans multiple lines. Message headers
+              that are longer than  $header_size_limit  characters  are  trun-
+              cated.
+
+       disable_mime_input_processing
+              While  receiving mail, give no special treatment to MIME related
+              message headers; all text after the initial message  headers  is
+              considered  to  be  part  of  the  message body. This means that
+              header_checks is applied to all the initial message headers, and
+              that body_checks is applied to the remainder of the message.
+
+              Note:  when  used  in  this  manner,  body_checks will process a
+              multi-line message header one line at a time.
+
+EXAMPLES
+       Header pattern to block attachments with bad file name extensions.  For
+       convenience, the PCRE /x flag is specified, so that there is no need to
+       collapse the pattern into a single line of text.  The  purpose  of  the
+       [[:xdigit:]] sub-expressions is to recognize Windows CLSID strings.
+
+       /etc/postfix/main.cf:
+           header_checks = pcre:/etc/postfix/header_checks.pcre
+
+       /etc/postfix/header_checks.pcre:
+           /^Content-(Disposition|Type).*name\s*=\s*"?([^;]*(\.|=2E)(
+             ade|adp|asp|bas|bat|chm|cmd|com|cpl|crt|dll|exe|
+             hlp|ht[at]|
+             inf|ins|isp|jse?|lnk|md[betw]|ms[cipt]|nws|
+             \{[[:xdigit:]]{8}(?:-[[:xdigit:]]{4}){3}-[[:xdigit:]]{12}\}|
+             ops|pcd|pif|prf|reg|sc[frt]|sh[bsm]|swf|
+             vb[esx]?|vxd|ws[cfh]))(\?=)?"?\s*(;|$)/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
+       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
+
+       Wietse Venema
+       Google, Inc.
+       111 8th Avenue
+       New York, NY 10011, USA
+
+                                                              HEADER_CHECKS(5)
+
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