X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/8a6eec04798d4000b00537e6c6f7f7f1596fccb8..360c049264151071203aee2f957472321ff0dc41:/doc/doc-docbook/spec.xfpt diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index 17c69a7a5..b6f387a1a 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -45,7 +45,7 @@ . Update the Copyright year (only) when changing content. . ///////////////////////////////////////////////////////////////////////////// -.set previousversion "4.80" +.set previousversion "4.83" .include ./local_params .set ACL "access control lists (ACLs)" @@ -5557,7 +5557,7 @@ unreachable. The next two lines are concerned with &'ident'& callbacks, as defined by RFC 1413 (hence their names): .code -rfc1413_query_hosts = * +rfc1413_hosts = * rfc1413_query_timeout = 0s .endd These settings cause Exim to avoid ident callbacks for all incoming SMTP calls. @@ -7005,7 +7005,6 @@ ${lookup dnsdb{a=one.host.com:two.host.com}} Thus, in the default case, as long as at least one of the DNS lookups yields some data, the lookup succeeds. -.new .cindex "DNSSEC" "dns lookup" Use of &(DNSSEC)& is controlled by a dnssec modifier. The possible keywords are @@ -7018,7 +7017,6 @@ is treated as equivalent to a temporary DNS error. The default is &"never"&. See also the &$lookup_dnssec_authenticated$& variable. -.wen @@ -7084,7 +7082,6 @@ With sufficiently modern LDAP libraries, Exim supports forcing TLS over regular LDAP connections, rather than the SSL-on-connect &`ldaps`&. See the &%ldap_start_tls%& option. -.new Starting with Exim 4.83, the initialization of LDAP with TLS is more tightly controlled. Every part of the TLS configuration can be configured by settings in &_exim.conf_&. Depending on the version of the client libraries installed on @@ -7094,7 +7091,6 @@ certificates. This revealed a nuance where the current UID that exim was running as could affect which config files it read. With Exim 4.83, these methods become optional, only taking effect if not specifically set in &_exim.conf_&. -.wen .section "LDAP quoting" "SECID68" @@ -7242,9 +7238,7 @@ them. The following names are recognized: &`USER `& set the DN, for authenticating the LDAP bind &`PASS `& set the password, likewise &`REFERRALS `& set the referrals parameter -.new &`SERVERS `& set alternate server list for this query only -.wen &`SIZE `& set the limit for the number of entries returned &`TIME `& set the maximum waiting time for a query .endd @@ -7266,7 +7260,6 @@ Netscape SDK; for OpenLDAP no action is taken. The TIME parameter (also a number of seconds) is passed to the server to set a server-side limit on the time taken to complete a search. -.new The SERVERS parameter allows you to specify an alternate list of ldap servers to use for an individual lookup. The global ldap_servers option provides a default list of ldap servers, and a single lookup can specify a single ldap @@ -7274,7 +7267,6 @@ server to use. But when you need to do a lookup with a list of servers that is different than the default list (maybe different order, maybe a completely different set of servers), the SERVERS parameter allows you to specify this alternate list. -.wen Here is an example of an LDAP query in an Exim lookup that uses some of these values. This is a single line, folded to fit on the page: @@ -8354,7 +8346,6 @@ Both &`+include_unknown`& and &`+ignore_unknown`& may appear in the same list. The effect of each one lasts until the next, or until the end of the list. -.new .section "Mixing wildcarded host names and addresses in host lists" &&& "SECTmixwilhos" .cindex "host list" "mixing names and addresses in" @@ -8390,7 +8381,6 @@ If the first &%accept%& fails, Exim goes on to try the second one. See chapter &`+ignore_unknown`&, which was discussed in depth in the first example in this section. .endlist -.wen .section "Temporary DNS errors when looking up host information" &&& @@ -8885,7 +8875,6 @@ the expansion result is an empty string. If the ACL returns defer the result is a forced-fail. Otherwise the expansion fails. -.new .vitem "&*${certextract{*&<&'field'&>&*}{*&<&'certificate'&>&*}&&& {*&<&'string2'&>&*}{*&<&'string3'&>&*}}*&" .cindex "expansion" "extracting cerificate fields" @@ -8899,8 +8888,8 @@ the certificate. Supported fields are: &`serial_number `& &`subject `& RFC4514 DN &`issuer `& RFC4514 DN -&`notbefore `& -&`notafter `& +&`notbefore `& time +&`notafter `& time &`sig_algorithm `& &`signature `& &`subj_altname `& tagged list @@ -8919,6 +8908,22 @@ extracted is used. Some field names take optional modifiers, appended and separated by commas. +The field selectors marked as "RFC4514" above +output a Distinguished Name string which is +not quite +parseable by Exim as a comma-separated tagged list +(the exceptions being elements containin commas). +RDN elements of a single type may be selected by +a modifier of the type label; if so the expansion +result is a list (newline-separated by default). +The separator may be changed by another modifer of +a right angle-bracket followed immediately by the new separator. +Recognised RDN type labels include "CN", "O", "OU" and "DC". + +The field selectors marked as "time" above +may output a number of seconds since epoch +if the modifier "int" is used. + The field selectors marked as "list" above return a list, newline-separated by default, (embedded separator characters in elements are doubled). @@ -8931,14 +8936,7 @@ Elements of only one type may be selected by a modifier which is one of "dns", "uri" or "mail"; if so the elenment tags are omitted. -The field selectors marked as "RFC4514" above -output a Distinguished Name string which is -not quite -parseable by Exim as a comma-separated tagged list -(the exceptions being elements containin commas). - -Field values are generally presented in human-readable form. -.wen +If not otherwise noted field values are presented in human-readable form. .vitem "&*${dlfunc{*&<&'file'&>&*}{*&<&'function'&>&*}{*&<&'arg'&>&*}&&& {*&<&'arg'&>&*}...}*&" @@ -9587,11 +9585,23 @@ expansion item above. {*&<&'string2'&>&*}}*&" .cindex "expansion" "running a command" .cindex "&%run%& expansion item" -The command and its arguments are first expanded separately, and then the -command is run in a separate process, but under the same uid and gid. As in -other command executions from Exim, a shell is not used by default. If you want +The command and its arguments are first expanded as one string. The string is +split apart into individual arguments by spaces, and then the command is run +in a separate process, but under the same uid and gid. As in other command +executions from Exim, a shell is not used by default. If the command requires a shell, you must explicitly code it. +Since the arguments are split by spaces, when there is a variable expansion +which has an empty result, it will cause the situation that the argument will +simply be omitted when the program is actually executed by Exim. If the +script/program requires a specific number of arguments and the expanded +variable could possibly result in this empty expansion, the variable must be +quoted. This is more difficult if the expanded variable itself could result +in a string containing quotes, because it would interfere with the quotes +around the command arguments. A possible guard against this is to wrap the +variable in the &%sg%& operator to change any quote marks to some other +character. + The standard input for the command exists, but is empty. The standard output and standard error are set to the same file descriptor. .cindex "return code" "from &%run%& expansion" @@ -10987,6 +10997,13 @@ precedes the expansion of the string. For example, the commands available in Exim filter files include an &%if%& command with its own regular expression matching condition. +.new +.vitem "&$acl_arg1$&, &$acl_arg2$&, etc" +Within an acl condition, expansion condition or expansion item +any arguments are copied to these variables, +any unused variables being made empty. +.wen + .vitem "&$acl_c...$&" Values can be placed in these variables by the &%set%& modifier in an ACL. They can be given any name that starts with &$acl_c$& and is at least six characters @@ -11008,6 +11025,12 @@ message is received, the values of these variables are saved with the message, and can be accessed by filters, routers, and transports during subsequent delivery. +.new +.vitem &$acl_narg$& +Within an acl condition, expansion condition or expansion item +this variable has the number of arguments. +.wen + .vitem &$acl_verify_message$& .vindex "&$acl_verify_message$&" After an address verification has failed, this variable contains the failure @@ -11546,7 +11569,6 @@ ability to find the amount of free space (only true for experimental systems), the space value is -1. See also the &%check_log_space%& option. -.new .vitem &$lookup_dnssec_authenticated$& .vindex "&$lookup_dnssec_authenticated$&" This variable is set after a DNS lookup done by @@ -11554,7 +11576,6 @@ a dnsdb lookup expansion, dnslookup router or smtp transport. It will be empty if &(DNSSEC)& was not requested, &"no"& if the result was not labelled as authenticated data and &"yes"& if it was. -.wen .vitem &$mailstore_basename$& .vindex "&$mailstore_basename$&" @@ -12093,7 +12114,8 @@ received. It is empty if there was no successful authentication. See also .vitem &$sender_host_dnssec$& .vindex "&$sender_host_dnssec$&" -If &$sender_host_name$& has been populated (by reference, &%hosts_lookup%& or +If an attempt to populate &$sender_host_name$& has been made +(by reference, &%hosts_lookup%& or otherwise) then this boolean will have been set true if, and only if, the resolver library states that the reverse DNS was authenticated data. At all other times, this variable is false. @@ -12332,7 +12354,6 @@ on an outbound SMTP connection; the meaning of this depends upon the TLS implementation used. If TLS has not been negotiated, the value will be 0. -.new .vitem &$tls_in_ourcert$& .vindex "&$tls_in_ourcert$&" This variable refers to the certificate presented to the peer of an @@ -12340,9 +12361,7 @@ inbound connection when the message was received. It is only useful as the argument of a &%certextract%& expansion item, &%md5%& or &%sha1%& operator, or a &%def%& condition. -.wen -.new .vitem &$tls_in_peercert$& .vindex "&$tls_in_peercert$&" This variable refers to the certificate presented by the peer of an @@ -12350,25 +12369,20 @@ inbound connection when the message was received. It is only useful as the argument of a &%certextract%& expansion item, &%md5%& or &%sha1%& operator, or a &%def%& condition. -.wen -.new .vitem &$tls_out_ourcert$& .vindex "&$tls_out_ourcert$&" This variable refers to the certificate presented to the peer of an outbound connection. It is only useful as the argument of a &%certextract%& expansion item, &%md5%& or &%sha1%& operator, or a &%def%& condition. -.wen -.new .vitem &$tls_out_peercert$& .vindex "&$tls_out_peercert$&" This variable refers to the certificate presented by the peer of an outbound connection. It is only useful as the argument of a &%certextract%& expansion item, &%md5%& or &%sha1%& operator, or a &%def%& condition. -.wen .vitem &$tls_in_certificate_verified$& .vindex "&$tls_in_certificate_verified$&" @@ -12713,8 +12727,9 @@ option), the interfaces and ports on which it listens are controlled by the following options: .ilist -&%daemon_smtp_ports%& contains a list of default ports. (For backward -compatibility, this option can also be specified in the singular.) +&%daemon_smtp_ports%& contains a list of default ports +or service names. +(For backward compatibility, this option can also be specified in the singular.) .next &%local_interfaces%& contains list of interface IP addresses on which to listen. Each item may optionally also specify a port. @@ -12815,7 +12830,8 @@ value of &%daemon_smtp_ports%& is no longer relevant in this example.) Exim supports the obsolete SSMTP protocol (also known as SMTPS) that was used before the STARTTLS command was standardized for SMTP. Some legacy clients still use this protocol. If the &%tls_on_connect_ports%& option is set to a -list of port numbers, connections to those ports must use SSMTP. The most +list of port numbers or service names, +connections to those ports must use SSMTP. The most common use of this option is expected to be .code tls_on_connect_ports = 465 @@ -13212,6 +13228,7 @@ listed in more than one group. .row &%tls_crl%& "certificate revocation list" .row &%tls_dh_max_bits%& "clamp D-H bit count suggestion" .row &%tls_dhparam%& "DH parameters for server" +.row &%tls_ocsp_file%& "location of server certificate status proof" .row &%tls_on_connect_ports%& "specify SSMTP (SMTPS) ports" .row &%tls_privatekey%& "location of server private key" .row &%tls_remember_esmtp%& "don't reset after starting TLS" @@ -16331,6 +16348,13 @@ prior to the 4.80 release, as Debian used to patch Exim to raise the minimum acceptable bound from 1024 to 2048. +.option tls_ocsp_file main string&!! unset +This option +must if set expand to the absolute path to a file which contains a current +status proof for the server's certificate, as obtained from the +Certificate Authority. + + .option tls_on_connect_ports main "string list" unset This option specifies a list of incoming SSMTP (aka SMTPS) ports that should operate the obsolete SSMTP (SMTPS) protocol, where a TLS session is immediately @@ -17816,7 +17840,6 @@ when there is a DNS lookup error. -.new .option dnssec_request_domains dnslookup "domain list&!!" unset .cindex "MX record" "security" .cindex "DNSSEC" "MX lookup" @@ -17825,11 +17848,9 @@ when there is a DNS lookup error. DNS lookups for domains matching &%dnssec_request_domains%& will be done with the dnssec request bit set. This applies to all of the SRV, MX A6, AAAA, A lookup sequence. -.wen -.new .option dnssec_require_domains dnslookup "domain list&!!" unset .cindex "MX record" "security" .cindex "DNSSEC" "MX lookup" @@ -17839,7 +17860,6 @@ DNS lookups for domains matching &%dnssec_request_domains%& will be done with the dnssec request bit set. Any returns not having the Authenticated Data bit (AD bit) set wil be ignored and logged as a host-lookup failure. This applies to all of the SRV, MX A6, AAAA, A lookup sequence. -.wen @@ -22746,7 +22766,6 @@ See the &%search_parents%& option in chapter &<>& for more details. -.new .option dnssec_request_domains smtp "domain list&!!" unset .cindex "MX record" "security" .cindex "DNSSEC" "MX lookup" @@ -22755,11 +22774,9 @@ details. DNS lookups for domains matching &%dnssec_request_domains%& will be done with the dnssec request bit set. This applies to all of the SRV, MX A6, AAAA, A lookup sequence. -.wen -.new .option dnssec_require_domains smtp "domain list&!!" unset .cindex "MX record" "security" .cindex "DNSSEC" "MX lookup" @@ -22769,7 +22786,6 @@ DNS lookups for domains matching &%dnssec_request_domains%& will be done with the dnssec request bit set. Any returns not having the Authenticated Data bit (AD bit) set wil be ignored and logged as a host-lookup failure. This applies to all of the SRV, MX A6, AAAA, A lookup sequence. -.wen @@ -22995,6 +23011,18 @@ hard failure if required. See also &%hosts_try_auth%&, and chapter &<>& for details of authentication. +.option hosts_request_ocsp smtp "host list&!!" * +.cindex "TLS" "requiring for certain servers" +Exim will request a Certificate Status on a +TLS session for any host that matches this list. +&%tls_verify_certificates%& should also be set for the transport. + +.option hosts_require_ocsp smtp "host list&!!" unset +.cindex "TLS" "requiring for certain servers" +Exim will request, and check for a valid Certificate Status being given, on a +TLS session for any host that matches this list. +&%tls_verify_certificates%& should also be set for the transport. + .option hosts_require_tls smtp "host list&!!" unset .cindex "TLS" "requiring for certain servers" Exim will insist on using a TLS session when delivering to any host that @@ -25363,7 +25391,7 @@ dovecot_plain: driver = dovecot public_name = PLAIN server_socket = /var/run/dovecot/auth-client - server_set_id = $auth2 + server_set_id = $auth1 dovecot_ntlm: driver = dovecot @@ -26154,12 +26182,79 @@ certificate is supplied, &$tls_in_peerdn$& is empty. .cindex "TLS" "revoked certificates" .cindex "revocation list" .cindex "certificate" "revocation list" +.cindex "OCSP" "stapling" Certificate issuing authorities issue Certificate Revocation Lists (CRLs) when certificates are revoked. If you have such a list, you can pass it to an Exim server using the global option called &%tls_crl%& and to an Exim client using an identically named option for the &(smtp)& transport. In each case, the value of the option is expanded and must then be the name of a file that contains a CRL in PEM format. +The downside is that clients have to periodically re-download a potentially huge +file from every certificate authority the know of. + +The way with most moving parts at query time is Online Certificate +Status Protocol (OCSP), where the client verifies the certificate +against an OCSP server run by the CA. This lets the CA track all +usage of the certs. It requires running software with access to the +private key of the CA, to sign the responses to the OCSP queries. OCSP +is based on HTTP and can be proxied accordingly. + +The only widespread OCSP server implementation (known to this writer) +comes as part of OpenSSL and aborts on an invalid request, such as +connecting to the port and then disconnecting. This requires +re-entering the passphrase each time some random client does this. + +The third way is OCSP Stapling; in this, the server using a certificate +issued by the CA periodically requests an OCSP proof of validity from +the OCSP server, then serves it up inline as part of the TLS +negotiation. This approach adds no extra round trips, does not let the +CA track users, scales well with number of certs issued by the CA and is +resilient to temporary OCSP server failures, as long as the server +starts retrying to fetch an OCSP proof some time before its current +proof expires. The downside is that it requires server support. + +Unless Exim is built with the support disabled, +or with GnuTLS earlier than version 3.1.3, +support for OCSP stapling is included. + +There is a global option called &%tls_ocsp_file%&. +The file specified therein is expected to be in DER format, and contain +an OCSP proof. Exim will serve it as part of the TLS handshake. This +option will be re-expanded for SNI, if the &%tls_certificate%& option +contains &`tls_in_sni`&, as per other TLS options. + +Exim does not at this time implement any support for fetching a new OCSP +proof. The burden is on the administrator to handle this, outside of +Exim. The file specified should be replaced atomically, so that the +contents are always valid. Exim will expand the &%tls_ocsp_file%& option +on each connection, so a new file will be handled transparently on the +next connection. + +When built with OpenSSL Exim will check for a valid next update timestamp +in the OCSP proof; if not present, or if the proof has expired, it will be +ignored. + +For the client to be able to verify the stapled OCSP the server must +also supply, in its stapled information, any intermediate +certificates for the chain leading to the OCSP proof from the signer +of the server certificate. There may be zero or one such. These +intermediate certificates should be added to the server OCSP stapling +file named by &%tls_ocsp_file%&. + +Note that the proof only covers the terminal server certificate, +not any of the chain from CA to it. + +.code + A helper script "ocsp_fetch.pl" for fetching a proof from a CA + OCSP server is supplied. The server URL may be included in the + server certificate, if the CA is helpful. + + One failure mode seen was the OCSP Signer cert expiring before the end + of validity of the OCSP proof. The checking done by Exim/OpenSSL + noted this as invalid overall, but the re-fetch script did not. +.endd + + .section "Configuring an Exim client to use TLS" "SECID185" @@ -26215,6 +26310,19 @@ The &%tls_verify_hosts%& and &%tls_try_verify_hosts%& options restrict certificate verification to the listed servers. Verification either must or need not succeed respectively. +The &(smtp)& transport has two OCSP-related options: +&%hosts_require_ocsp%&; a host-list for which a Certificate Status +is requested and required for the connection to proceed. The default +value is empty. +&%hosts_request_ocsp%&; a host-list for which (additionally) +a Certificate Status is requested (but not necessarily verified). The default +value is "*" meaning that requests are made unless configured +otherwise. + +The host(s) should also be in &%hosts_require_tls%&, and +&%tls_verify_certificates%& configured for the transport, +for OCSP to be relevant. + If &%tls_require_ciphers%& is set on the &(smtp)& transport, it must contain a list of permitted cipher suites. If either of these checks fails, delivery to @@ -26300,6 +26408,9 @@ during TLS session handshake, to permit alternative values to be chosen: .next .vindex "&%tls_verify_certificates%&" &%tls_verify_certificates%& +.next +.vindex "&%tls_ocsp_file%&" +&%tls_verify_certificates%& .endlist Great care should be taken to deal with matters of case, various injection @@ -28301,7 +28412,6 @@ This condition checks whether the sending host (the client) is authorized to send email. Details of how this works are given in section &<>&. -.new .vitem &*verify&~=&~header_names_ascii*& .cindex "&%verify%& ACL condition" .cindex "&ACL;" "verifying header names only ASCII" @@ -28316,7 +28426,6 @@ allowable characters are decimal ASCII values 33 through 126. Exim itself will handle headers with non-ASCII characters, but it can cause problems for downstream applications, so this option will allow their detection and rejection in the DATA ACL's. -.wen .vitem &*verify&~=&~header_sender/*&<&'options'&> .cindex "&%verify%& ACL condition" @@ -34930,10 +35039,8 @@ or (in case &*-a*& switch is specified) .code exim -bp .endd -.new The &*-C*& option is used to specify an alternate &_exim.conf_& which might contain alternate exim configuration the queue management might be using. -.wen to obtain a queue listing, and then greps the output to select messages that match given criteria. The following selection options are available: