TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto
TLS_INCLUDE=-I/usr/local/openssl/include/
.endd
+.new
+.cindex "pkg-config" "OpenSSL"
+If you have &'pkg-config'& available, then instead you can just use:
+.code
+SUPPORT_TLS=yes
+USE_OPENSSL_PC=openssl
+.endd
+.wen
.cindex "USE_GNUTLS"
If GnuTLS is installed, you should set
.code
TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt
TLS_INCLUDE=-I/usr/gnu/include
.endd
+.new
+.cindex "pkg-config" "GnuTLS"
+If you have &'pkg-config'& available, then instead you can just use:
+.code
+SUPPORT_TLS=yes
+USE_GNUTLS=yes
+USE_GNUTLS_PC=gnutls
+.endd
+.wen
+
You do not need to set TLS_INCLUDE if the relevant directory is already
specified in INCLUDE. Details of how to configure Exim to make use of TLS are
given in chapter &<<CHAPTLS>>&.
binary, attempts to configure Exim to use it cause run time configuration
errors.
+.new
+.cindex "pkg-config" "lookups"
+.cindex "pkg-config" "authenticators"
+Many systems now use a tool called &'pkg-config'& to encapsulate information
+about how to compile against a library; Exim has some initial support for
+being able to use pkg-config for lookups and authenticators. For any given
+makefile variable which starts &`LOOKUP_`& or &`AUTH_`&, you can add a new
+variable with the &`_PC`& suffix in the name and assign as the value the
+name of the package to be queried. The results of querying via the
+&'pkg-config'& command will be added to the appropriate Makefile variables
+with &`+=`& directives, so your version of &'make'& will need to support that
+syntax. For instance:
+.code
+LOOKUP_SQLITE=yes
+LOOKUP_SQLITE_PC=sqlite3
+AUTH_GSASL=yes
+AUTH_GSASL_PC=libgsasl
+AUTH_HEIMDAL_GSSAPI=yes
+AUTH_HEIMDAL_GSSAPI_PC=heimdal-gssapi
+.endd
+.wen
+
.cindex "Perl" "including support for"
Exim can be linked with an embedded Perl interpreter, allowing Perl
subroutines to be called during string expansion. To enable this facility,
the DB_UNKNOWN option. This enables it to handle any of the types of database
that the library supports, and can be useful for accessing DBM files created by
other applications. (For earlier DB versions, DB_HASH is always used.)
+.new
+.next
+.cindex "lookup" "dbmjz"
+.cindex "lookup" "dbm &-- embedded NULs"
+.cindex "sasldb2"
+.cindex "dbmjz lookup type"
+&(dbmjz)&: This is the same as &(dbm)&, except that the lookup key is
+interpreted as an Exim list; the elements of the list are joined together with
+ASCII NUL characters to form the lookup key. An example usage would be to
+authenticate incoming SMTP calls using the passwords from Cyrus SASL's
+&_/etc/sasldb2_& file with the &(gsasl)& authenticator or Exim's own
+&(cram_md5)& authenticator.
+.wen
.next
.cindex "lookup" "dbmnz"
.cindex "lookup" "dbm &-- terminating zero"
.cindex "binary zero" "in lookup key"
.cindex "Courier"
.cindex "&_/etc/userdbshadow.dat_&"
-.cindex "dmbnz lookup type"
+.cindex "dbmnz lookup type"
&(dbmnz)&: This is the same as &(dbm)&, except that a terminating binary zero
is not included in the key that is passed to the DBM library. You may need this
if you want to look up data in files that are created by or shared with some
below in section &<<SECTexpansionitems>>& onwards. Backslash is used as an
escape character, as described in the following section.
+Whether a string is expanded depends upon the context. Usually this is solely
+dependent upon the option for which a value is sought; in this documentation,
+options for which string expansion is performed are marked with † after
+the data type. ACL rules always expand strings. A couple of expansion
+conditions do not expand some of the brace-delimited branches, for security
+reasons.
+
.section "Literal text in expanded strings" "SECTlittext"
As a special case, the numerical value of an empty string is taken as
zero.
+In all cases, a relative comparator OP is testing if <&'string1'&> OP
+<&'string2'&>; the above example is checking if &$message_size$& is larger than
+10M, not if 10M is larger than &$message_size$&.
+
.vitem &*bool&~{*&<&'string'&>&*}*&
.cindex "expansion" "boolean parsing"
value is retained during message delivery, except during outbound SMTP
deliveries.
+.new
+.vitem &$tls_sni$&
+.vindex "&$tls_sni$&"
+.cindex "TLS" "Server Name Indication"
+When a TLS session is being established, if the client sends the Server
+Name Indication extension, the value will be placed in this variable.
+If the variable appears in &%tls_certificate%& then this option and
+&%tls_privatekey%& will be re-expanded early in the TLS session, to permit
+a different certificate to be presented (and optionally a different key to be
+used) to the client, based upon the value of the SNI extension.
+
+The value will be retained for the lifetime of the message, and not changed
+during outbound SMTP.
+
+This is currently only available when using OpenSSL, built with support for
+SNI.
+.wen
+
.vitem &$tod_bsdinbox$&
.vindex "&$tod_bsdinbox$&"
The time of day and the date, in the format required for BSD-style mailbox
transport driver.
-.option openssl_options main "string list" +dont_insert_empty_fragments
+.option openssl_options main "string list" unset
.cindex "OpenSSL "compatibility options"
This option allows an administrator to adjust the SSL options applied
by OpenSSL to connections. It is given as a space-separated list of items,
-each one to be +added or -subtracted from the current value. The default
-value is one option which happens to have been set historically. You can
-remove all options with:
-.code
-openssl_options = -all
-.endd
+each one to be +added or -subtracted from the current value.
+
This option is only available if Exim is built against OpenSSL. The values
available for this option vary according to the age of your OpenSSL install.
The &"all"& value controls a subset of flags which are available, typically
Note that adjusting the options can have severe impact upon the security of
SSL as used by Exim. It is possible to disable safety checks and shoot
yourself in the foot in various unpleasant ways. This option should not be
-adjusted lightly. An unrecognised item will be detected at by invoking Exim
-with the &%-bV%& flag.
+adjusted lightly. An unrecognised item will be detected at startup, by
+invoking Exim with the &%-bV%& flag.
+
+.new
+Historical note: prior to release 4.78, Exim defaulted this value to
+"+dont_insert_empty_fragments", which may still be needed for compatibility
+with some clients, but which lowers security by increasing exposure to
+some now infamous attacks.
+.wen
An example:
.code
-openssl_options = -all +microsoft_big_sslv3_buffer
+openssl_options = -all +microsoft_big_sslv3_buffer +dont_insert_empty_fragments
.endd
+Possible options may include:
+.ilist
+&`all`&
+.ilist
+&`allow_unsafe_legacy_renegotiation`&
+.ilist
+&`cipher_server_preference`&
+.ilist
+&`dont_insert_empty_fragments`&
+.ilist
+&`ephemeral_rsa`&
+.ilist
+&`legacy_server_connect`&
+.ilist
+&`microsoft_big_sslv3_buffer`&
+.ilist
+&`microsoft_sess_id_bug`&
+.ilist
+&`msie_sslv2_rsa_padding`&
+.ilist
+&`netscape_challenge_bug`&
+.ilist
+&`netscape_reuse_cipher_change_bug`&
+.ilist
+&`no_compression`&
+.ilist
+&`no_session_resumption_on_renegotiation`&
+.ilist
+&`no_sslv2`&
+.ilist
+&`no_sslv3`&
+.ilist
+&`no_ticket`&
+.ilist
+&`no_tlsv1`&
+.ilist
+&`no_tlsv1_1`&
+.ilist
+&`no_tlsv1_2`&
+.ilist
+&`single_dh_use`&
+.ilist
+&`single_ecdh_use`&
+.ilist
+&`ssleay_080_client_dh_bug`&
+.ilist
+&`sslref2_reuse_cert_type_bug`&
+.ilist
+&`tls_block_padding_bug`&
+.ilist
+&`tls_d5_bug`&
+.ilist
+&`tls_rollback_bug`&
+.endlist
+
.option oracle_servers main "string list" unset
.cindex "Oracle" "server list"
.code
AUTH_CRAM_MD5=yes
AUTH_CYRUS_SASL=yes
+.new
+AUTH_DOVECOT=yes
+AUTH_GSASL=yes
+AUTH_HEIMDAL_GSSAPI=yes
+.wen
AUTH_PLAINTEXT=yes
AUTH_SPA=yes
.endd
in &_Local/Makefile_&, respectively. The first of these supports the CRAM-MD5
authentication mechanism (RFC 2195), and the second provides an interface to
-the Cyrus SASL authentication library. The third can be configured to support
+the Cyrus SASL authentication library.
+.new
+The third is an interface to Dovecot's authentication system, delegating the
+work via a socket interface.
+The fourth provides an interface to the GNU SASL authentication library, which
+provides mechanisms but typically not data sources.
+The fifth provides direct access to Heimdal GSSAPI, geared for Kerberos, but
+supporting setting a server keytab.
+The sixth can be configured to support
the PLAIN authentication mechanism (RFC 2595) or the LOGIN mechanism, which is
-not formally documented, but used by several MUAs. The fourth authenticator
+not formally documented, but used by several MUAs. The seventh authenticator
supports Microsoft's &'Secure Password Authentication'& mechanism.
+.wen
The authenticators are configured using the same syntax as other drivers (see
section &<<SECTfordricon>>&). If no authenticators are required, no
authenticators, followed by general discussion of the way authentication works
in Exim.
+.new
+&*Beware:*& the meaning of &$auth1$&, &$auth2$&, ... varies on a per-driver and
+per-mechanism basis. Please read carefully to determine which variables hold
+account labels such as usercodes and which hold passwords or other
+authenticating data.
+
+Note that some mechanisms support two different identifiers for accounts: the
+&'authentication id'& and the &'authorization id'&. The contractions &'authn'&
+and &'authz'& are commonly encountered. The American spelling is standard here.
+Conceptually, authentication data such as passwords are tied to the identifier
+used to authenticate; servers may have rules to permit one user to act as a
+second user, so that after login the session is treated as though that second
+user had logged in. That second user is the &'authorization id'&. A robust
+configuration might confirm that the &'authz'& field is empty or matches the
+&'authn'& field. Often this is just ignored. The &'authn'& can be considered
+as verified data, the &'authz'& as an unverified request which the server might
+choose to honour.
+
+A &'realm'& is a text string, typically a domain name, presented by a server
+to a client to help it select an account and credentials to use. In some
+mechanisms, the client and server provably agree on the realm, but clients
+typically can not treat the realm as secure data to be blindly trusted.
+.wen
+
.section "Generic options for authenticators" "SECID168"
is used directly to control authentication. See section &<<SECTplainserver>>&
for details.
+.new
+For the &(gsasl)& authenticator, this option is required for various
+mechanisms; see chapter &<<CHAPgsasl>>& for details.
+.wen
+
For the other authenticators, &%server_condition%& can be used as an additional
authentication or authorization mechanism that is applied after the other
authenticator conditions succeed. If it is set, it is expanded when the
Note that this expansion explicitly forces failure if the lookup fails
because &$auth1$& contains an unknown user name.
+.new
+As another example, if you wish to re-use a Cyrus SASL sasldb2 file without
+using the relevant libraries, you need to know the realm to specify in the
+lookup and then ask for the &"userPassword"& attribute for that user in that
+realm, with:
+.code
+cyrusless_crammd5:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ server_secret = ${lookup{$auth1:mail.example.org:userPassword}\
+ dbmjz{/etc/sasldb2}}
+ server_set_id = $auth1
+.endd
+.wen
.section "Using cram_md5 as a client" "SECID177"
.cindex "options" "&(cram_md5)& authenticator (client)"
Kerberos, note that because of limitations in the GSSAPI interface,
changing the server keytab might need to be communicated down to the Kerberos
layer independently. The mechanism for doing so is dependent upon the Kerberos
-implementation. For example, for Heimdal, the environment variable KRB5_KTNAME
+implementation.
+.new
+For example, for older releases of Heimdal, the environment variable KRB5_KTNAME
may be set to point to an alternative keytab file. Exim will pass this
variable through from its own inherited environment when started as root or the
Exim user. The keytab file needs to be readable by the Exim user.
+With newer releases of Heimdal, a setuid Exim may cause Heimdal to discard the
+environment variable. In practice, for those releases, the Cyrus authenticator
+is not a suitable interface for GSSAPI (Kerberos) support. Instead, consider
+the &(heimdal_gssapi)& authenticator, described in chapter &<<CHAPheimdalgss>>&
+.wen
.section "Using cyrus_sasl as a server" "SECID178"
server_set_id = $auth1
.endd
-.option server_realm cyrus_sasl string unset
+.new
+.option server_realm cyrus_sasl string&!! unset
This specifies the SASL realm that the server claims to be in.
+.wen
.option server_service cyrus_sasl string &`smtp`&
.ecindex IIDdcotauth2
+. ////////////////////////////////////////////////////////////////////////////
+. ////////////////////////////////////////////////////////////////////////////
+.new
+.chapter "The gsasl authenticator" "CHAPgsasl"
+.scindex IIDgsaslauth1 "&(gsasl)& authenticator"
+.scindex IIDgsaslauth2 "authenticators" "&(gsasl)&"
+.cindex "authentication" "GNU SASL"
+.cindex "authentication" "SASL"
+.cindex "authentication" "EXTERNAL"
+.cindex "authentication" "ANONYMOUS"
+.cindex "authentication" "PLAIN"
+.cindex "authentication" "LOGIN"
+.cindex "authentication" "DIGEST-MD5"
+.cindex "authentication" "CRAM-MD5"
+.cindex "authentication" "SCRAM-SHA-1"
+The &(gsasl)& authenticator provides server integration for the GNU SASL
+library and the mechanisms it provides. This is new as of the 4.78 release
+and there are a few areas where the library does not let Exim smoothly
+scale to handle future authentication mechanisms, so no guarantee can be
+made that any particular new authentication mechanism will be supported
+without code changes in Exim.
+
+
+.option server_channelbinding gsasl bool false
+Some authentication mechanisms are able to use external context at both ends
+of the session to bind the authentication to that context, and fail the
+authentication process if that context differs. Specifically, some TLS
+ciphersuites can provide identifying information about the cryptographic
+context.
+
+This means that certificate identity and verification becomes a non-issue,
+as a man-in-the-middle attack will cause the correct client and server to
+see different identifiers and authentication will fail.
+
+This is currently only supported when using the GnuTLS library. This is
+only usable by mechanisms which support "channel binding"; at time of
+writing, that's the SCRAM family.
+
+This defaults off to ensure smooth upgrade across Exim releases, in case
+this option causes some clients to start failing. Some future release
+of Exim may switch the default to be true.
+
+
+.option server_hostname gsasl string&!! "see below"
+This option selects the hostname that is used when communicating with the
+library. The default value is &`$primary_hostname`&.
+Some mechanisms will use this data.
+
+
+.option server_mech gsasl string "see below"
+This option selects the authentication mechanism this driver should use. The
+default is the value of the generic &%public_name%& option. This option allows
+you to use a different underlying mechanism from the advertised name. For
+example:
+.code
+sasl:
+ driver = gsasl
+ public_name = X-ANYTHING
+ server_mech = CRAM-MD5
+ server_set_id = $auth1
+.endd
+
+
+.option server_password gsasl string&!! unset
+Various mechanisms need access to the cleartext password on the server, so
+that proof-of-possession can be demonstrated on the wire, without sending
+the password itself.
+
+The data available for lookup varies per mechanism.
+In all cases, &$auth1$& is set to the &'authentication id'&.
+The &$auth2$& variable will always be the &'authorization id'& (&'authz'&)
+if available, else the empty string.
+The &$auth3$& variable will always be the &'realm'& if available,
+else the empty string.
+
+A forced failure will cause authentication to defer.
+
+If using this option, it may make sense to set the &%server_condition%&
+option to be simply "true".
+
+
+.option server_realm gsasl string&!! unset
+This specifies the SASL realm that the server claims to be in.
+Some mechanisms will use this data.
+
+
+.option server_scram_iter gsasl string&!! unset
+This option provides data for the SCRAM family of mechanisms.
+&$auth1$& is not available at evaluation time.
+(This may change, as we receive feedback on use)
+
+
+.option server_scram_salt gsasl string&!! unset
+This option provides data for the SCRAM family of mechanisms.
+&$auth1$& is not available at evaluation time.
+(This may change, as we receive feedback on use)
+
+
+.option server_service gsasl string &`smtp`&
+This is the SASL service that the server claims to implement.
+Some mechanisms will use this data.
+
+
+.section "&(gsasl)& auth variables" "SECTgsaslauthvar"
+.vindex "&$auth1$&, &$auth2$&, etc"
+These may be set when evaluating specific options, as detailed above.
+They will also be set when evaluating &%server_condition%&.
+
+Unless otherwise stated below, the &(gsasl)& integration will use the following
+meanings for these variables:
+
+.ilist
+.vindex "&$auth1$&"
+&$auth1$&: the &'authentication id'&
+.next
+.vindex "&$auth2$&"
+&$auth2$&: the &'authorization id'&
+.next
+.vindex "&$auth3$&"
+&$auth3$&: the &'realm'&
+.endlist
+
+On a per-mechanism basis:
+
+.ilist
+.cindex "authentication" "EXTERNAL"
+EXTERNAL: only &$auth1$& is set, to the possibly empty &'authorization id'&;
+the &%server_condition%& option must be present.
+.next
+.cindex "authentication" "ANONYMOUS"
+ANONYMOUS: only &$auth1$& is set, to the possibly empty &'anonymous token'&;
+the &%server_condition%& option must be present.
+.next
+.cindex "authentication" "GSSAPI"
+GSSAPI: &$auth1$& will be set to the &'GSSAPI Display Name'&;
+&$auth2$& will be set to the &'authorization id'&,
+the &%server_condition%& option must be present.
+.endlist
+
+An &'anonymous token'& is something passed along as an unauthenticated
+identifier; this is analogous to FTP anonymous authentication passing an
+email address, or software-identifier@, as the "password".
+
+
+An example showing the password having the realm specified in the callback
+and demonstrating a Cyrus SASL to GSASL migration approach is:
+.code
+gsasl_cyrusless_crammd5:
+ driver = gsasl
+ public_name = CRAM-MD5
+ server_realm = imap.example.org
+ server_password = ${lookup{$auth1:$auth3:userPassword}\
+ dbmjz{/etc/sasldb2}{$value}fail}
+ server_set_id = ${quote:$auth1}
+ server_condition = yes
+.endd
+
+.wen
+
+. ////////////////////////////////////////////////////////////////////////////
+. ////////////////////////////////////////////////////////////////////////////
+
+.new
+.chapter "The heimdal_gssapi authenticator" "CHAPheimdalgss"
+.scindex IIDheimdalgssauth1 "&(heimdal_gssapi)& authenticator"
+.scindex IIDheimdalgssauth2 "authenticators" "&(heimdal_gssapi)&"
+.cindex "authentication" "GSSAPI"
+.cindex "authentication" "Kerberos"
+The &(heimdal_gssapi)& authenticator provides server integration for the
+Heimdal GSSAPI/Kerberos library, permitting Exim to set a keytab pathname
+reliably.
+
+.option server_hostname heimdal_gssapi string&!! "see below"
+This option selects the hostname that is used, with &%server_service%&,
+for constructing the GSS server name, as a &'GSS_C_NT_HOSTBASED_SERVICE'&
+identifier. The default value is &`$primary_hostname`&.
+
+.option server_keytab heimdal_gssapi string&!! unset
+If set, then Heimdal will not use the system default keytab (typically
+&_/etc/krb5.keytab_&) but instead the pathname given in this option.
+The value should be a pathname, with no &"file:"& prefix.
+
+.option server_service heimdal_gssapi string&!! "smtp"
+This option specifies the service identifier used, in conjunction with
+&%server_hostname%&, for building the identifer for finding credentials
+from the keytab.
+
+
+.section "&(heimdal_gssapi)& auth variables" "SECTheimdalgssauthvar"
+Beware that these variables will typically include a realm, thus will appear
+to be roughly like an email address already. The &'authzid'& in &$auth2$& is
+not verified, so a malicious client can set it to anything.
+
+The &$auth1$& field should be safely trustable as a value from the Key
+Distribution Center. Note that these are not quite email addresses.
+Each identifier is for a role, and so the left-hand-side may include a
+role suffix. For instance, &"joe/admin@EXAMPLE.ORG"&.
+
+.vindex "&$auth1$&, &$auth2$&, etc"
+.ilist
+.vindex "&$auth1$&"
+&$auth1$&: the &'authentication id'&, set to the GSS Display Name.
+.next
+.vindex "&$auth2$&"
+&$auth2$&: the &'authorization id'&, sent within SASL encapsulation after
+authentication. If that was empty, this will also be set to the
+GSS Display Name.
+.endlist
+
+.wen
+
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
git://git.exim.org / users / jgh / exim.git / blobdiff