-. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.82 2010/06/06 02:08:50 pdp Exp $
+. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.88 2010/06/14 18:51:09 pdp Exp $
.
. /////////////////////////////////////////////////////////////////////////////
. This is the primary source of the Exim Manual. It is an xfpt document that is
. the <bookinfo> element must also be updated for each new edition.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.71"
-.set version "4.72"
+.set previousversion "4.72"
+.set version "4.73"
.set ACL "access control lists (ACLs)"
.set I " "
<author><firstname>Exim</firstname><surname>Maintainers</surname></author>
<authorinitials>EM</authorinitials>
<revhistory><revision>
- <revnumber>4.72</revnumber>
- <date>29 May 2010</date>
+ <revnumber>4.73</revnumber>
+ <date>19 Nov 2010</date>
<authorinitials>EM</authorinitials>
</revision></revhistory>
<copyright><year>2009</year><holder>University of Cambridge</holder></copyright>
waiting for it by the time it recovers, and sending them in a single SMTP
connection is clearly beneficial. Whenever a delivery to a remote host is
deferred,
-
.cindex "hints database"
Exim makes a note in its hints database, and whenever a successful
SMTP delivery has happened, it looks to see if any other messages are waiting
.section "Use of tcpwrappers" "SECID27"
+.new
.cindex "tcpwrappers, building Exim to support"
.cindex "USE_TCP_WRAPPERS"
+.cindex "TCP_WRAPPERS_DAEMON_NAME"
+.cindex "tcp_wrappers_daemon_name"
Exim can be linked with the &'tcpwrappers'& library in order to check incoming
SMTP calls using the &'tcpwrappers'& control files. This may be a convenient
alternative to Exim's own checking facilities for installations that are
CFLAGS=-O -I/usr/local/include
EXTRALIBS_EXIM=-L/usr/local/lib -lwrap
.endd
-in &_Local/Makefile_&. The name to use in the &'tcpwrappers'& control files is
-&"exim"&. For example, the line
+in &_Local/Makefile_&. The daemon name to use in the &'tcpwrappers'& control
+files is &"exim"&. For example, the line
.code
exim : LOCAL 192.168.1. .friendly.domain.example
.endd
in your &_/etc/hosts.allow_& file allows connections from the local host, from
the subnet 192.168.1.0/24, and from all hosts in &'friendly.domain.example'&.
-All other connections are denied. Consult the &'tcpwrappers'& documentation for
+All other connections are denied. The daemon name used by &'tcpwrappers'&
+can be changed at build time by setting TCP_WRAPPERS_DAEMON_NAME in
+in &_Local/Makefile_&, or by setting tcp_wrappers_daemon_name in the
+configure file. Consult the &'tcpwrappers'& documentation for
further details.
-
+.wen
.section "Including support for IPv6" "SECID28"
The same output is generated if the Exim binary is called with no options and
no arguments.
+.new
.vitem &%--version%&
.oindex "&%--version%&"
This option is an alias for &%-bV%& and causes version information to be
displayed.
+.wen
.vitem &%-B%&<&'type'&>
.oindex "&%-B%&"
Exim behaves in exactly the same way as it does when receiving a message via
the listening daemon.
+.new
.vitem &%-bmalware%&&~<&'filename'&>
.oindex "&%-bmalware%&"
.cindex "testing", "malware"
.cindex "malware scan test"
This debugging option causes Exim to scan the given file,
-using the malware scanning framework. The option of av_scanner influences
-this option, so if av_scanner's value is dependent upon an expansion then
-the expansion should have defaults which apply to this invocation. Exim will
-have changed working directory before resolving the filename, so using fully
-qualified pathnames is advisable. This option requires admin privileges.
+using the malware scanning framework. The option of &%av_scanner%& influences
+this option, so if &%av_scanner%&'s value is dependent upon an expansion then
+the expansion should have defaults which apply to this invocation. ACLs are
+not invoked, so if &%av_scanner%& references an ACL variable then that variable
+will never be populated and &%-bmalware%& will fail.
+
+Exim will have changed working directory before resolving the filename, so
+using fully qualified pathnames is advisable. Exim will be running as the Exim
+user when it tries to open the file, rather than as the invoking user.
+This option requires admin privileges.
+
+The &%-bmalware%& option will not be extended to be more generally useful,
+there are better tools for file-scanning. This option exists to help
+administrators verify their Exim and AV scanner configuration.
+.wen
.vitem &%-bt%&
.oindex "&%-bt%&"
.cindex "version number of Exim"
This option causes Exim to write the current version number, compilation
number, and compilation date of the &'exim'& binary to the standard output.
-It also lists the DBM library this is being used, the optional modules (such as
+It also lists the DBM library that is being used, the optional modules (such as
specific lookup types), the drivers that are included in the binary, and the
name of the run time configuration file that is in use.
than a recipient address. This affects any rewriting and qualification that
might happen.
+.new
.vitem &%-C%&&~<&'filelist'&>
.oindex "&%-C%&"
.cindex "configuration file" "alternate"
file that exists is used. Failure to open an existing file stops Exim from
proceeding any further along the list, and an error is generated.
-When this option is used by a caller other than root or the Exim user, and the
-list is different from the compiled-in list, Exim gives up its root privilege
-immediately, and runs with the real and effective uid and gid set to those of
-the caller. However, if ALT_CONFIG_ROOT_ONLY is defined in
-&_Local/Makefile_&, root privilege is retained for &%-C%& only if the caller of
-Exim is root.
-
-That is, the Exim user is no longer privileged in this regard. This build-time
-option is not set by default in the Exim source distribution tarbundle.
-However, if you are using a &"packaged"& version of Exim (source or binary),
-the packagers might have enabled it.
-
-Setting ALT_CONFIG_ROOT_ONLY locks out the possibility of testing a
-configuration using &%-C%& right through message reception and delivery, even
-if the caller is root. The reception works, but by that time, Exim is running
-as the Exim user, so when it re-executes to regain privilege for the delivery,
-the use of &%-C%& causes privilege to be lost. However, root can test reception
-and delivery using two separate commands (one to put a message on the queue,
-using &%-odq%&, and another to do the delivery, using &%-M%&).
+When this option is used by a caller other than root, and the list is different
+from the compiled-in list, Exim gives up its root privilege immediately, and
+runs with the real and effective uid and gid set to those of the caller.
+However, if a TRUSTED_CONFIG_LIST file is defined in &_Local/Makefile_&, that
+file contains a list of full pathnames, one per line, for configuration files
+which are trusted. Root privilege is retained for any configuration file so
+listed, as long as the caller is the Exim user (or the user specified in the
+CONFIGURE_OWNER option, if any), and as long as the configuration file is
+not writeable by inappropriate users or groups.
+
+Leaving TRUSTED_CONFIG_LIST unset precludes the possibility of testing a
+configuration using &%-C%& right through message reception and delivery,
+even if the caller is root. The reception works, but by that time, Exim is
+running as the Exim user, so when it re-executes to regain privilege for the
+delivery, the use of &%-C%& causes privilege to be lost. However, root can
+test reception and delivery using two separate commands (one to put a message
+on the queue, using &%-odq%&, and another to do the delivery, using &%-M%&).
If ALT_CONFIG_PREFIX is defined &_in Local/Makefile_&, it specifies a
prefix string with which any file named in a &%-C%& command line option
caller is privileged, or unless it is an exotic configuration that does not
require privilege. No check is made on the owner or group of the files
specified by this option.
+.wen
+.new
.vitem &%-D%&<&'macro'&>=<&'value'&>
.oindex "&%-D%&"
.cindex "macro" "setting on command line"
If DISABLE_D_OPTION is defined in &_Local/Makefile_&, the use of &%-D%& is
completely disabled, and its use causes an immediate error exit.
+If WHITELIST_D_MACROS is defined in &_Local/Makefile_& then it should be a
+colon-separated list of macros which are considered safe and, if &%-D%& only
+supplies macros from this list, and the values are acceptable, then Exim will
+not give up root privilege if the caller is root, the Exim run-time user, or
+the CONFIGURE_OWNER, if set. This is a transition mechanism and is expected
+to be removed in the future. Acceptable values for the macros satisfy the
+regexp: &`^[A-Za-z0-9_/.-]*$`&
+
The entire option (including equals sign if present) must all be within one
command line item. &%-D%& can be used to set the value of a macro to the empty
string, in which case the equals sign is optional. These two commands are
exim '-D ABC = something' ...
.endd
&%-D%& may be repeated up to 10 times on a command line.
+.wen
.vitem &%-d%&<&'debug&~options'&>
.oindex "&%-d%&"
give a colon-separated list of file names, in which case Exim uses the first
existing file in the list.
+.new
.cindex "EXIM_USER"
.cindex "EXIM_GROUP"
.cindex "CONFIGURE_OWNER"
.cindex "configuration file" "ownership"
.cindex "ownership" "configuration file"
The run time configuration file must be owned by root or by the user that is
-specified at compile time by the EXIM_USER option, or by the user that is
specified at compile time by the CONFIGURE_OWNER option (if set). The
-configuration file must not be world-writeable or group-writeable, unless its
-group is the one specified at compile time by the EXIM_GROUP option or by the
+configuration file must not be world-writeable, or group-writeable unless its
+group is the root group or the one specified at compile time by the
CONFIGURE_GROUP option.
&*Warning*&: In a conventional configuration, where the Exim binary is setuid
to root, anybody who is able to edit the run time configuration file has an
-easy way to run commands as root. If you make your mail administrators members
-of the Exim group, but do not trust them with root, make sure that the run time
-configuration is not group writeable.
+easy way to run commands as root. If you specify a user or group in the
+CONFIGURE_OWNER or CONFIGURE_GROUP options, then that user and/or any users
+who are members of that group will trivially be able to obtain root privileges.
+
+Up to Exim version 4.72, the run time configuration file was also permitted to
+be writeable by the Exim user and/or group. That has been changed in Exim 4.73
+since it offered a simple privilege escalation for any attacker who managed to
+compromise the Exim user account.
A default configuration file, which will work correctly in simple situations,
is provided in the file &_src/configure.default_&. If CONFIGURE_FILE
CONFIGURE_FILE is a list, no default is automatically installed. Chapter
&<<CHAPdefconfil>>& is a &"walk-through"& discussion of the default
configuration.
-
+.wen
.section "Using a different configuration file" "SECID40"
.cindex "configuration file" "alternate"
A one-off alternate configuration can be specified by the &%-C%& command line
option, which may specify a single file or a list of files. However, when
-&%-C%& is used, Exim gives up its root privilege, unless called by root or the
-Exim user (or unless the argument for &%-C%& is identical to the built-in value
-from CONFIGURE_FILE). &%-C%& is useful mainly for checking the syntax of
-configuration files before installing them. No owner or group checks are done
-on a configuration file specified by &%-C%&.
-
-The privileged use of &%-C%& by the Exim user can be locked out by setting
-ALT_CONFIG_ROOT_ONLY in &_Local/Makefile_& when building Exim. However,
-if you do this, you also lock out the possibility of testing a
-configuration using &%-C%& right through message reception and delivery, even
-if the caller is root. The reception works, but by that time, Exim is running
-as the Exim user, so when it re-execs to regain privilege for the delivery, the
-use of &%-C%& causes privilege to be lost. However, root can test reception and
-delivery using two separate commands (one to put a message on the queue, using
-&%-odq%&, and another to do the delivery, using &%-M%&).
+&%-C%& is used, Exim gives up its root privilege, unless called by root (or
+unless the argument for &%-C%& is identical to the built-in value from
+CONFIGURE_FILE), or is listed in the TRUSTED_CONFIG_LIST file and the caller
+is the Exim user or the user specified in the CONFIGURE_OWNER setting. &%-C%&
+is useful mainly for checking the syntax of configuration files before
+installing them. No owner or group checks are done on a configuration file
+specified by &%-C%&, if root privilege has been dropped.
+
+Even the Exim user is not trusted to specify an arbitrary configuration file
+with the &%-C%& option to be used with root privileges, unless that file is
+listed in the TRUSTED_CONFIG_LIST file. This locks out the possibility of
+testing a configuration using &%-C%& right through message reception and
+delivery, even if the caller is root. The reception works, but by that time,
+Exim is running as the Exim user, so when it re-execs to regain privilege for
+the delivery, the use of &%-C%& causes privilege to be lost. However, root
+can test reception and delivery using two separate commands (one to put a
+message on the queue, using &%-odq%&, and another to do the delivery, using
+&%-M%&).
If ALT_CONFIG_PREFIX is defined &_in Local/Makefile_&, it specifies a
prefix string with which any file named in a &%-C%& command line option must
If DISABLE_D_OPTION is defined in &_Local/Makefile_&, the use of &%-D%& is
completely disabled, and its use causes an immediate error exit.
+.new
+The WHITELIST_D_MACROS option in &_Local/Makefile_& permits the binary builder
+to declare certain macro names trusted, such that root privilege will not
+necessarily be discarded.
+WHITELIST_D_MACROS defines a colon-separated list of macros which are
+considered safe and, if &%-D%& only supplies macros from this list, and the
+values are acceptable, then Exim will not give up root privilege if the caller
+is root, the Exim run-time user, or the CONFIGURE_OWNER, if set. This is a
+transition mechanism and is expected to be removed in the future. Acceptable
+values for the macros satisfy the regexp: &`^[A-Za-z0-9_/.-]*$`&
+.wen
+
Some sites may wish to use the same Exim binary on different machines that
share a file system, but to use different configuration files on each machine.
If CONFIGURE_FILE_USE_NODE is defined in &_Local/Makefile_&, Exim first
It is permitted to specify a space as the separator character. Further
white space is ignored.
-.new
.cindex "TXT record" "in &(dnsdb)& lookup"
For TXT records with multiple items of data, only the first item is returned,
unless a separator for them is specified using a comma after the separator
.endd
It is permitted to specify a space as the separator character. Further
white space is ignored.
-.wen
.section "Pseudo dnsdb record types" "SECID66"
.cindex "MX record" "in &(dnsdb)& lookup"
random().
+.new
.vitem &*${reverse_ip:*&<&'ipaddr'&>&*}*&
.cindex "expansion" "IP address"
This operator reverses an IP address; for IPv4 addresses, the result is in
.code
4.2.0.192 and 3.0.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2
.endd
+.wen
.vitem &*${rfc2047:*&<&'string'&>&*}*&
As a special case, the numerical value of an empty string is taken as
zero.
+
+.new
.vitem &*bool&~{*&<&'string'&>&*}*&
.cindex "expansion" "boolean parsing"
.cindex "&%bool%& expansion condition"
This condition turns a string holding a true or false representation into
a boolean state. It parses &"true"&, &"false"&, &"yes"& and &"no"&
(case-insensitively); also positive integer numbers map to true if non-zero,
-false if zero. Leading whitespace is ignored.
+false if zero. Leading and trailing whitespace is ignored.
All other string values will result in expansion failure.
When combined with ACL variables, this expansion condition will let you
.code
${if bool{$acl_m_privileged_sender} ...
.endd
+.wen
+
+
+.vitem &*bool_lax&~{*&<&'string'&>&*}*&
+.cindex "expansion" "boolean parsing"
+.cindex "&%bool_lax%& expansion condition"
+Like &%bool%&, this condition turns a string into a boolean state. But
+where &%bool%& accepts a strict set of strings, &%bool_lax%& uses the same
+loose definition that the Router &%condition%& option uses. The empty string
+and the values &"false"&, &"no"& and &"0"& map to false, all others map to
+true. Leading and trailing whitespace is ignored.
+
+Note that where &"bool{00}"& is false, &"bool_lax{00}"& is true.
.vitem &*crypteq&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
.cindex "expansion" "encrypted comparison"
the generic transport option &%message_size_limit%&, which limits the size of
message that an individual transport can process.
+.new
If you use a virus-scanner and set this option to to a value larger than the
maximum size that your virus-scanner is configured to support, you may get
failures triggered by large mails. The right size to configure for the
probably safest to just set it to a little larger than this value. Eg, with a
default Exim message size of 50M and a default ClamAV StreamMaxLength of 10M,
some problems may result.
+.wen
.option move_frozen_messages main boolean false
transport driver.
+.new
.option openssl_options main "string list" +dont_insert_empty_fragments
.cindex "OpenSSL "compatibility options"
This option allows an administrator to adjust the SSL options applied
.code
openssl_options = -all +microsoft_big_sslv3_buffer
.endd
+.wen
.option oracle_servers main "string list" unset
This specifies the transport driver that is to be used when a &%mail%& command
is used in a system filter.
+.new
.option system_filter_user main string unset
.cindex "uid (user id)" "system filter"
-If this option is not set, the system filter is run in the main Exim delivery
-process, as root. When the option is set, the system filter runs in a separate
-process, as the given user. Unless the string consists entirely of digits, it
+If this option is set to root, the system filter is run in the main Exim
+delivery process, as root. Otherwise, the system filter runs in a separate
+process, as the given user, defaulting to the Exim run-time user.
+Unless the string consists entirely of digits, it
is looked up in the password data. Failure to find the named user causes a
configuration error. The gid is either taken from the password data, or
specified by &%system_filter_group%&. When the uid is specified numerically,
If the system filter generates any pipe, file, or reply deliveries, the uid
under which the filter is run is used when transporting them, unless a
-transport option overrides. Normally you should set &%system_filter_user%& if
-your system filter generates these kinds of delivery.
+transport option overrides.
+.wen
.option tcp_nodelay main boolean true
If the result is any other value, the router is run (as this is the last
precondition to be evaluated, all the other preconditions must be true).
+.new
+This option is unique in that multiple &%condition%& options may be present.
+All &%condition%& options must succeed.
+.wen
+
The &%condition%& option provides a means of applying custom conditions to the
running of routers. Note that in the case of a simple conditional expansion,
the default expansion values are exactly what is wanted. For example:
.code
condition = ${if >{$message_age}{600}{true}{}}
.endd
+.new
+A multiple condition example, which succeeds:
+.code
+condition = ${if >{$message_age}{600}}
+condition = ${if !eq{${lc:$local_part}}{postmaster}}
+condition = foobar
+.endd
+.wen
If the expansion fails (other than forced failure) delivery is deferred. Some
of the other precondition options are common special cases that could in fact
be specified using &%condition%&.
apply to a command specified as a transport filter.
+.new
.option permit_coredump pipe boolean false
Normally Exim inhibits core-dumps during delivery. If you have a need to get
a core-dump of a pipe command, enable this command. This enables core-dumps
resource consumption can be quite high. Note also that Exim is typically
installed as a setuid binary and most operating systems will inhibit coredumps
of these by default, so further OS-specific action may be required.
+.wen
.option pipe_as_creator pipe boolean false
driver = plaintext
public_name = LOGIN
server_prompts = Username:: : Password::
- server_condition = ${if and{{
+ server_condition = ${if and{{ \
!eq{}{$auth1} }{ \
ldapauth{user="cn=${quote_ldap_dn:$auth1},ou=people,o=example.org" \
pass=${quote:$auth2} \
your resources.
+.new
+.section "The SMTP DKIM ACL" "SECTDKIMACL"
+The &%acl_smtp_dkim%& ACL is available only when Exim is compiled with DKIM support
+enabled (which is the default).
+
+The ACL test specified by &%acl_smtp_dkim%& happens after a message has been
+received, and is executed for each DKIM signature found in a message. If not
+otherwise specified, the default action is to accept.
+
+For details on the operation of DKIM, see chapter &<<CHID12>>&.
+.wen
+
+
.section "The SMTP MIME ACL" "SECID194"
The &%acl_smtp_mime%& option is available only when Exim is compiled with the
content-scanning extension. For details, see chapter &<<CHAPexiscan>>&.
Notice that we put back the lower cased version afterwards, assuming that
is what is wanted for subsequent tests.
+.new
.vitem &*control&~=&~debug/*&<&'options'&>
.cindex "&ACL;" "enabling debug logging"
.cindex "debugging" "enabling from an ACL"
control = debug/opts=+expand+acl
control = debug/tag=.$message_exim_id/opts=+expand
.endd
+.wen
.vitem &*control&~=&~enforce_sync*& &&&
&*control&~=&~no_enforce_sync*&
use the &%demime%& condition (see section &<<SECTdemimecond>>&) before the
&%malware%& condition.
+.new
Beware the interaction of Exim's &%message_size_limit%& with any size limits
imposed by your anti-virus scanner.
+.wen
Here is a very simple scanning example:
.code
&%spam%& condition for its side effects (see the variables below), you can make
it always return &"true"& by appending &`:true`& to the username.
+.new
.cindex "spam scanning" "returned variables"
When the &%spam%& condition is run, it sets up a number of expansion
variables. These variables are saved with the received message, thus they are
available for use at delivery time.
+.wen
.vlist
.vitem &$spam_score$&
and EHLO act as RSET; VRFY, EXPN, ETRN and HELP, act
as NOOP; QUIT quits.
-No policy checking is done for BSMTP input. That is, no ACL is run at anytime.
-In this respect it is like non-SMTP local input.
+Minimal policy checking is done for BSMTP input. Only the non-SMTP
+ACL is run in the same way as for non-SMTP local input.
If an error is detected while reading a message, including a missing &"."& at
the end, Exim gives up immediately. It writes details of the error to the
into the Exim account from running a privileged Exim with an arbitrary
configuration file, and using it to break into other accounts.
.next
-If ALT_CONFIG_ROOT_ONLY is defined, root privilege is retained for &%-C%&
-and &%-D%& only if the caller of Exim is root. Without it, the Exim user may
-also use &%-C%& and &%-D%& and retain privilege. Setting this option locks out
-the possibility of testing a configuration using &%-C%& right through message
-reception and delivery, even if the caller is root. The reception works, but by
-that time, Exim is running as the Exim user, so when it re-execs to regain
-privilege for the delivery, the use of &%-C%& causes privilege to be lost.
-However, root can test reception and delivery using two separate commands.
-ALT_CONFIG_ROOT_ONLY is not set by default.
+.new
+If a non-trusted configuration file (i.e. not the default configuration file
+or one which is trusted by virtue of being listed in the TRUSTED_CONFIG_LIST
+file) is specified with &%-C%&, or if macros are given with &%-D%& (but see
+the next item), then root privilege is retained only if the caller of Exim is
+root. This locks out the possibility of testing a configuration using &%-C%&
+right through message reception and delivery, even if the caller is root. The
+reception works, but by that time, Exim is running as the Exim user, so when
+it re-execs to regain privilege for the delivery, the use of &%-C%& causes
+privilege to be lost. However, root can test reception and delivery using two
+separate commands.
+.wen
+.next
+The WHITELIST_D_MACROS build option declares some macros to be safe to override
+with &%-D%& if the real uid is one of root, the Exim run-time user or the
+CONFIGURE_OWNER, if defined. The potential impact of this option is limited by
+requiring the run-time value supplied to &%-D%& to match a regex that errs on
+the restrictive side. Requiring build-time selection of safe macros is onerous
+but this option is intended solely as a transition mechanism to permit
+previously-working configurations to continue to work after release 4.73.
.next
If DISABLE_D_OPTION is defined, the use of the &%-D%& command line option
is disabled.
.oindex "&%-D%&"
If the &%-C%& option is used to specify an alternate configuration file, or if
the &%-D%& option is used to define macro values for the configuration, and the
-calling process is not running as root or the Exim user, the uid and gid are
-changed to those of the calling process.
-However, if ALT_CONFIG_ROOT_ONLY is defined in &_Local/Makefile_&, only
-root callers may use &%-C%& and &%-D%& without losing privilege, and if
-DISABLE_D_OPTION is set, the &%-D%& option may not be used at all.
+calling process is not running as root, the uid and gid are changed to those of
+the calling process.
+However, if DISABLE_D_OPTION is defined in &_Local/Makefile_&, the &%-D%&
+option may not be used at all.
+If WHITELIST_D_MACROS is defined in &_Local/Makefile_&, then some macro values
+can be supplied if the calling process is running as root, the Exim run-time
+user or CONFIGURE_OWNER, if defined.
.next
.oindex "&%-be%&"
.oindex "&%-bf%&"
git://git.exim.org / exim.git / blobdiff