X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/c9433c53ad292c2f7ec05aa9d083767f95d07858..509a8839d50d1e688b794975378214cc201a9697:/doc/doc-docbook/spec.xfpt?ds=sidebyside diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index 540a9cbf8..ef8fc6836 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -54,7 +54,7 @@ .set drivernamemax "64" .macro copyyear -2021 +2022 .endmacro . ///////////////////////////////////////////////////////////////////////////// @@ -97,6 +97,21 @@ .itable none 0 0 2 $1 left $2 left .endmacro + +. --- A macro for a "tainted" marker, done as a one-element table +.macro tmark +.itable none 0 0 1 10pt left +.row &'Tainted'& +.endtable +.endmacro +. --- A macro for a tainted variable, adding a taint-marker +. --- and including the .vitem and .vindex +.macro tvar +.vitem $1 +.vindex $1 +.tmark +.endmacro + . --- A macro that generates .row, but puts &I; at the start of the first . --- argument, thus indenting it. Assume a minimum of two arguments, and . --- allow up to four arguments, which is as many as we'll ever need. @@ -239,14 +254,6 @@ failure report bounce message - - de-tainting - tainting, de-tainting - - - detainting - tainting, de-tainting - dialup intermittently connected hosts @@ -766,17 +773,17 @@ the Exim documentation, &"spool"& is always used in the first sense. .chapter "Incorporated code" "CHID2" .cindex "incorporated code" .cindex "regular expressions" "library" -.cindex "PCRE" +.cindex "PCRE2" .cindex "OpenDMARC" A number of pieces of external code are included in the Exim distribution. .ilist Regular expressions are supported in the main Exim program and in the -Exim monitor using the freely-distributable PCRE library, copyright -© University of Cambridge. The source to PCRE is no longer shipped with -Exim, so you will need to use the version of PCRE shipped with your system, +Exim monitor using the freely-distributable PCRE2 library, copyright +© University of Cambridge. The source to PCRE2 is not longer shipped with +Exim, so you will need to use the version of PCRE2 shipped with your system, or obtain and install the full version of the library from -&url(ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre). +&url(https://github.com/PhilipHazel/pcre2/releases). .next .cindex "cdb" "acknowledgment" Support for the cdb (Constant DataBase) lookup method is provided by code @@ -1422,6 +1429,7 @@ check an address given in the SMTP EXPN command (see the &%expn%& option). If the &%domains%& option is set, the domain of the address must be in the set of domains that it defines. .cindex "tainted data" "de-tainting" +.cindex "de-tainting" "using router domains option" A match verifies the variable &$domain$& (which carries tainted data) and assigns an untainted value to the &$domain_data$& variable. Such an untainted value is often needed in the transport. @@ -1745,20 +1753,20 @@ overridden if necessary. A C99-capable compiler will be required for the build. -.section "PCRE library" "SECTpcre" -.cindex "PCRE library" -Exim no longer has an embedded PCRE library as the vast majority of -modern systems include PCRE as a system library, although you may need to -install the PCRE package or the PCRE development package for your operating -system. If your system has a normal PCRE installation the Exim build +.section "PCRE2 library" "SECTpcre" +.cindex "PCRE2 library" +Exim no longer has an embedded regular-expression library as the vast majority of +modern systems include PCRE2 as a system library, although you may need to +install the PCRE2 package or the PCRE2 development package for your operating +system. If your system has a normal PCRE2 installation the Exim build process will need no further configuration. If the library or the -headers are in an unusual location you will need to either set the PCRE_LIBS +headers are in an unusual location you will need to either set the PCRE2_LIBS and INCLUDE directives appropriately, -or set PCRE_CONFIG=yes to use the installed &(pcre-config)& command. +or set PCRE2_CONFIG=yes to use the installed &(pcre-config)& command. If your operating system has no -PCRE support then you will need to obtain and build the current PCRE -from &url(ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/). -More information on PCRE is available at &url(https://www.pcre.org/). +PCRE2 support then you will need to obtain and build the current PCRE2 +from &url(https://github.com/PhilipHazel/pcre2/releases). +More information on PCRE2 is available at &url(https://www.pcre.org/). .section "DBM libraries" "SECTdb" .cindex "DBM libraries" "discussion of" @@ -1811,9 +1819,13 @@ the traditional &'ndbm'& interface. .next To complicate things further, there are several very different versions of the Berkeley DB package. Version 1.85 was stable for a very long time, releases -2.&'x'& and 3.&'x'& were current for a while, but the latest versions when Exim last revamped support were numbered 4.&'x'&. -Maintenance of some of the earlier releases has ceased. All versions of -Berkeley DB could be obtained from +2.&'x'& and 3.&'x'& were current for a while, +.new +but the latest versions when Exim last revamped support were numbered 5.&'x'&. +Maintenance of some of the earlier releases has ceased, +and Exim no longer supports versions before 3.&'x'&. +.wen +All versions of Berkeley DB could be obtained from &url(http://www.sleepycat.com/), which is now a redirect to their new owner's page with far newer versions listed. It is probably wise to plan to move your storage configurations away from @@ -1837,6 +1849,9 @@ USE_DB=yes .endd Similarly, for gdbm you set USE_GDBM, and for tdb you set USE_TDB. An error is diagnosed if you set more than one of these. +.new +You can set USE_NDBM if needed to override an operating system default. +.wen At the lowest level, the build-time configuration sets none of these options, thereby assuming an interface of type (1). However, some operating system @@ -1851,7 +1866,11 @@ in one of these lines: .code DBMLIB = -ldb DBMLIB = -ltdb +DBMLIB = -lgdbm -lgdbm_compat .endd +.new +The last of those was for a Linux having GDBM provide emulated NDBM facilities. +.wen Settings like that will work if the DBM library is installed in the standard place. Sometimes it is not, and the library's header file may also not be in the default path. You may need to set INCLUDE to specify where the header @@ -2587,6 +2606,25 @@ use of Exim's filtering capabilities, you should make the document entitled +.section "Running the daemon" SECTdaemonLaunch +The most common command line for launching the Exim daemon looks like +.code +exim -bd -q5m +.endd +This starts a daemon which +.ilist +listens for incoming smtp connections, launching handler processes for +each new one +.next +starts a queue-runner process every five minutes, to inspect queued messages +and run delivery attempts on any that have arrived at their retry time +.endlist +Should a queue run take longer than the time between queue-runner starts, +they will run in parallel. +Numbers of jobs of the various types are subject to policy controls +defined in the configuration. + + .section "Upgrading Exim" "SECID36" .cindex "upgrading Exim" If you are already running Exim on your host, building and installing a new @@ -6635,9 +6673,9 @@ Chapter &<>& covers both. .chapter "Regular expressions" "CHAPregexp" .cindex "regular expressions" "library" -.cindex "PCRE" +.cindex "PCRE2" Exim supports the use of regular expressions in many of its options. It -uses the PCRE regular expression library; this provides regular expression +uses the PCRE2 regular expression library; this provides regular expression matching that is compatible with Perl 5. The syntax and semantics of regular expressions is discussed in online Perl manpages, in @@ -6649,10 +6687,10 @@ O'Reilly (see &url(http://www.oreilly.com/catalog/regex2/)). . --- to the old URL for now. 2018-09-07. The documentation for the syntax and semantics of the regular expressions that -are supported by PCRE is included in the PCRE distribution, and no further -description is included here. The PCRE functions are called from Exim using -the default option settings (that is, with no PCRE options set), except that -the PCRE_CASELESS option is set when the matching is required to be +are supported by PCRE2 is included in the PCRE2 distribution, and no further +description is included here. The PCRE2 functions are called from Exim using +the default option settings (that is, with no PCRE2 options set), except that +the PCRE2_CASELESS option is set when the matching is required to be case-insensitive. In most cases, when a regular expression is required in an Exim configuration, @@ -6736,6 +6774,9 @@ domains = ${lookup{$sender_host_address}lsearch{/some/file}} domains = lsearch;/some/file .endd The first uses a string expansion, the result of which must be a domain list. +.new +The key for an expansion-style lookup must be given explicitly. +.wen No strings have been specified for a successful or a failing lookup; the defaults in this case are the looked-up data and an empty string, respectively. The expansion takes place before the string is processed as a list, and the @@ -6747,6 +6788,7 @@ file that is searched could contain lines like this: When the lookup succeeds, the result of the expansion is a list of domains (and possibly other types of item that are allowed in domain lists). .cindex "tainted data" "de-tainting" +.cindex "de-tainting" "using a lookup expansion"" The result of the expansion is not tainted. In the second example, the lookup is a single item in a domain list. It causes @@ -6760,6 +6802,12 @@ domain2: Any data that follows the keys is not relevant when checking that the domain matches the list item. +.new +The key for a list-style lookup is implicit, from the lookup context, if +the lookup is a single-key type (see below). +For query-style lookup types the key must be given explicitly. +.wen + It is possible, though no doubt confusing, to use both kinds of lookup at once. Consider a file containing lines like this: .code @@ -6794,20 +6842,26 @@ The &'single-key'& type requires the specification of a file in which to look, and a single key to search for. The key must be a non-empty string for the lookup to succeed. The lookup type determines how the file is searched. .cindex "tainted data" "single-key lookups" -The file string may not be tainted +The file string may not be tainted. .cindex "tainted data" "de-tainting" +.cindex "de-tainting" "using a single-key lookup" All single-key lookups support the option &"ret=key"&. If this is given and the lookup (either underlying implementation or cached value) returns data, the result is replaced with a non-tainted version of the lookup key. -.cindex "tainted data" "de-tainting" .next .cindex "query-style lookup" "definition of" The &'query-style'& type accepts a generalized database query. No particular key value is assumed by Exim for query-style lookups. You can use whichever Exim variables you need to construct the database query. +.cindex "tainted data" "quoting for lookups" +.new +If tainted data is used in the query then it should be quuted by +using the &*${quote_*&<&'lookup-type'&>&*:*&<&'string'&>&*}*& expansion operator +appropriate for the lookup. +.wen .endlist The code for each lookup type is in a separate source file that is included in @@ -6961,7 +7015,7 @@ IPv4, in dotted-quad form. (Exim converts IPv4-mapped IPv6 addresses to this notation before executing the lookup.) One option is supported, "ret=full", to request the return of the entire line -rather than omitting the key porttion. +rather than omitting the key portion. Note however that the key portion will have been de-quoted. .next @@ -8796,6 +8850,7 @@ or a &%domains%& condition in an ACL statement, the value is preserved in the &$domain_data$& variable and can be referred to in other router options or other statements in the same ACL. .cindex "tainted data" "de-tainting" +.cindex "de-tainting" "using ACL domains condition" The value will be untainted. &*Note*&: If the data result of the lookup (as opposed to the key) @@ -8837,6 +8892,7 @@ whether or not the query succeeds. However, when a lookup is used for the &%domains%& option on a router, the value is preserved in the &$domain_data$& variable and can be referred to in other options. .cindex "tainted data" "de-tainting" +.cindex "de-tainting" "using router domains option" The value will be untainted. .next @@ -9589,8 +9645,6 @@ reasons, .cindex expansion "tainted data" and expansion of data deriving from the sender (&"tainted data"&) is not permitted (including acessing a file using a tainted name). -The main config option &%allow_insecure_tainted_data%& can be used as -mitigation during uprades to more secure configurations. Common ways of obtaining untainted equivalents of variables with tainted values @@ -10556,7 +10610,7 @@ sending the request. Values are &"yes"& (the default) or &"no"& &*tls*& Controls the use of TLS on the connection. Values are &"yes"& or &"no"& (the default). -If it is enabled, a shutdown as descripbed above is never done. +If it is enabled, a shutdown as described above is never done. .endlist @@ -10628,16 +10682,32 @@ expansion items. This item inserts &"raw"& header lines. It is described with the &%header%& expansion item in section &<>& above. -.vitem "&*${run{*&<&'command'&>&*&~*&<&'args'&>&*}{*&<&'string1'&>&*}&&& +.vitem "&*${run <&'options'&> {*&<&'command&~arg&~list'&>&*}{*&<&'string1'&>&*}&&& {*&<&'string2'&>&*}}*&" .cindex "expansion" "running a command" .cindex "&%run%& expansion item" -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 +This item runs an external command, as a subprocess. +.new +One option is supported after the word &'run'&, comma-separated. + +If the option &'preexpand'& is not used, +the command string is split into individual arguments by spaces +and then each argument is expanded. +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. +The command name may not be tainted, but the remaining arguments can be. + +&*Note*&: if tainted arguments are used, they are supplied by a +potential attacker; +a careful assessment for security vulnerabilities should be done. +If the option &'preexpand'& is used, +.wen +the command and its arguments are first expanded as one string. The result is +split apart into individual arguments by spaces, and then the command is run +as above. 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 @@ -10648,6 +10718,9 @@ 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. +.new +Neither the command nor any argument may be tainted. +.wen The standard input for the command exists, but is empty. The standard output and standard error are set to the same file descriptor. @@ -10765,16 +10838,16 @@ SRS encoding. See SECT &<>& for details. -.vitem &*${substr{*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*& +.vitem &*${substr{*&<&'start'&>&*}{*&<&'len'&>&*}{*&<&'subject'&>&*}}*& .cindex "&%substr%& expansion item" .cindex "substring extraction" .cindex "expansion" "substring extraction" The three strings are expanded; the first two must yield numbers. Call them <&'n'&> and <&'m'&>. If you are using fixed values for these numbers, that is, -if <&'string1'&> and <&'string2'&> do not change when they are expanded, you +if <&'start'&> and <&'len'&> do not change when they are expanded, you can use the simpler operator notation that avoids some of the braces: .code -${substr__:} +${substr__:} .endd The second number is optional (in both notations). If it is absent in the simpler format, the preceding underscore must also be @@ -11867,6 +11940,20 @@ ${if inlisti{Needle}{fOo:NeeDLE:bAr}} ${if forany{fOo:NeeDLE:bAr}{eqi{$item}{Needle}}} .endd +.new +The variable &$value$& will be set for a successful match and can be +used in the success clause of an &%if%& expansion item using the condition. +.cindex "tainted data" "de-tainting" +.cindex "de-tainting" "using an inlist expansion condition" +It will have the same taint status as the list; expansions such as +.code +${if inlist {$h_mycode:} {0 : 1 : 42} {$value}} +.endd +can be used for de-tainting. +Any previous &$value$& is restored after the if. +.wen + + .vitem &*isip&~{*&<&'string'&>&*}*& &&& &*isip4&~{*&<&'string'&>&*}*& &&& &*isip6&~{*&<&'string'&>&*}*& @@ -12063,6 +12150,19 @@ item can be used, as in all address lists, to cause subsequent items to have their local parts matched casefully. Domains are always matched caselessly. +.new +The variable &$value$& will be set for a successful match and can be +used in the success clause of an &%if%& expansion item using the condition. +.cindex "tainted data" "de-tainting" +.cindex "de-tainting" "using a match_local_part expansion condition" +It will have the same taint status as the list; expansions such as +.code +${if match_local_part {$local_part} {alice : bill : charlotte : dave} {$value}} +.endd +can be used for de-tainting. +Any previous &$value$& is restored after the if. +.wen + Note that <&'string2'&> is not itself subject to string expansion, unless Exim was built with the EXPAND_LISTMATCH_RHS option. @@ -12079,8 +12179,9 @@ matched using &%match_ip%&. .cindex "&%pam%& expansion condition" &'Pluggable Authentication Modules'& (&url(https://mirrors.edge.kernel.org/pub/linux/libs/pam/)) are a facility that is -available in the latest releases of Solaris and in some GNU/Linux -distributions. The Exim support, which is intended for use in conjunction with +available in Solaris +and in some GNU/Linux distributions. +The Exim support, which is intended for use in conjunction with the SMTP AUTH command, is available only if Exim is compiled with .code SUPPORT_PAM=yes @@ -12257,6 +12358,16 @@ parsed but not evaluated. This section contains an alphabetical list of all the expansion variables. Some of them are available only when Exim is compiled with specific options such as support for TLS or the content scanning extension. +.new +.cindex "tainted data" +Variables marked as &'tainted'& are likely to carry data supplied by +a potential attacker. +Variables without such marking may also, depending on how their +values are created. +Such variables should not be further expanded, +used as filenames +or used as command-line arguments for external commands. +.wen .vlist .vitem "&$0$&, &$1$&, etc" @@ -12271,6 +12382,9 @@ variables may also be set externally by some other matching process which 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 +If the subject string was tainted then any captured substring will also be. +.wen .vitem "&$acl_arg1$&, &$acl_arg2$&, etc" Within an acl condition, expansion condition or expansion item @@ -12396,11 +12510,10 @@ authentication, which means this variable could also be visible in all of the ACL's as well. -.vitem &$authenticated_sender$& +.tvar &$authenticated_sender$& .cindex "sender" "authenticated" .cindex "authentication" "sender" .cindex "AUTH" "on MAIL command" -.vindex "&$authenticated_sender$&" When acting as a server, Exim takes note of the AUTH= parameter on an incoming SMTP MAIL command if it believes the sender is sufficiently trusted, as described in section &<>&. Unless the data is the string @@ -12552,8 +12665,7 @@ the following data from the lookup: the list's domain name, the key that was looked up, the contents of any associated TXT record, and the value from the main A record. See section &<>& for more details. -.vitem &$domain$& -.vindex "&$domain$&" +.tvar &$domain$& When an address is being routed, or delivered on its own, this variable contains the domain. Uppercase letters in the domain are converted into lower case for &$domain$&. @@ -12654,6 +12766,7 @@ There may be other characters following the minor version. This value may be overridden by the &%exim_version%& main config option. .vitem &$header_$&<&'name'&> +.tmark This is not strictly an expansion variable. It is expansion syntax for inserting the message header line with the given name. Note that the name must be terminated by colon or white space, because it may contain a wide variety of @@ -12714,6 +12827,7 @@ allows you, for example, to do things like this: deny hosts = net-lsearch;/some/file message = $host_data .endd + .vitem &$host_lookup_deferred$& .cindex "host name" "lookup, failure of" .vindex "&$host_lookup_deferred$&" @@ -12796,8 +12910,7 @@ This variable contains the system load average, multiplied by 1000 so that it is an integer. For example, if the load average is 0.21, the value of the variable is 210. The value is recomputed every time the variable is referenced. -.vitem &$local_part$& -.vindex "&$local_part$&" +.tvar &$local_part$& When an address is being routed, or delivered on its own, this variable contains the local part. When a number of addresses are being delivered together (for example, multiple RCPT commands in an SMTP @@ -12972,11 +13085,10 @@ This variable is set at the start of a delivery attempt to contain the number of seconds since the message was received. It does not change during a single delivery attempt. -.vitem &$message_body$& +.tvar &$message_body$& .cindex "body of message" "expansion variable" .cindex "message body" "in expansion" .cindex "binary zero" "in message body" -.vindex "&$message_body$&" .oindex "&%message_body_visible%&" This variable contains the initial portion of a message's body while it is being delivered, and is intended mainly for use in filter files. The maximum @@ -12989,10 +13101,9 @@ easier to search for phrases that might be split over a line break. However, this can be disabled by setting &%message_body_newlines%& to be true. Binary zeros are always converted into spaces. -.vitem &$message_body_end$& +.tvar &$message_body_end$& .cindex "body of message" "expansion variable" .cindex "message body" "in expansion" -.vindex "&$message_body_end$&" This variable contains the final portion of a message's body while it is being delivered. The format and maximum size are as for &$message_body$&. @@ -13019,15 +13130,13 @@ received. &*Note*&: This is &'not'& the contents of the &'Message-ID:'& header line; it is the local id that Exim assigns to the message, for example: &`1BXTIK-0001yO-VA`&. -.vitem &$message_headers$& -.vindex &$message_headers$& +.tvar &$message_headers$& This variable contains a concatenation of all the header lines when a message is being processed, except for lines added by routers or transports. The header lines are separated by newline characters. Their contents are decoded in the same way as a header line that is inserted by &%bheader%&. -.vitem &$message_headers_raw$& -.vindex &$message_headers_raw$& +.tvar &$message_headers_raw$& This variable is like &$message_headers$& except that no processing of the contents of header lines is done. @@ -13104,9 +13213,8 @@ details, see section &<>&. These variables are counters that can be incremented by means of the &%add%& command in filter files. -.vitem &$original_domain$& +.tvar &$original_domain$& .vindex "&$domain$&" -.vindex "&$original_domain$&" When a top-level address is being processed for delivery, this contains the same value as &$domain$&. However, if a &"child"& address (for example, generated by an alias, forward, or filter file) is being processed, this @@ -13119,9 +13227,8 @@ If a new address is created by means of a &%deliver%& command in a system filter, it is set up with an artificial &"parent"& address. This has the local part &'system-filter'& and the default qualify domain. -.vitem &$original_local_part$& +.tvar &$original_local_part$& .vindex "&$local_part$&" -.vindex "&$original_local_part$&" When a top-level address is being processed for delivery, this contains the same value as &$local_part$&, unless a prefix or suffix was removed from the local part, because &$original_local_part$& always contains the full local @@ -13159,13 +13266,11 @@ messages received via the command line, this is the uid of the sending user. For messages received by SMTP over TCP/IP, this is normally the uid of the Exim user. -.vitem &$parent_domain$& -.vindex "&$parent_domain$&" +.tvar &$parent_domain$& This variable is similar to &$original_domain$& (see above), except that it refers to the immediately preceding parent address. -.vitem &$parent_local_part$& -.vindex "&$parent_local_part$&" +.tvar &$parent_local_part$& This variable is similar to &$original_local_part$& (see above), except that it refers to the immediately preceding parent address. @@ -13184,6 +13289,11 @@ This is not an expansion variable, but is mentioned here because the string (described under &%transport_filter%& in chapter &<>&). It cannot be used in general expansion strings, and provokes an &"unknown variable"& error if encountered. +.new +&*Note*&: This value permits data supplied by a potential attacker to +be used in the command for a &(pipe)& transport. +Such configurations should be carefully assessed for security vulnerbilities. +.wen .vitem &$primary_hostname$& .vindex "&$primary_hostname$&" @@ -13273,8 +13383,7 @@ including the one added by Exim (so its value is always greater than zero). It is available in the DATA ACL, the non-SMTP ACL, and while routing and delivering. -.vitem &$received_for$& -.vindex "&$received_for$&" +.tvar &$received_for$& If there is only a single recipient address in an incoming message, this variable contains that address when the &'Received:'& header line is being built. The value is copied after recipient rewriting has happened, but before @@ -13366,8 +13475,7 @@ MAIL). The main use of this variable is expected to be to distinguish between rejections of MAIL and rejections of RCPT. -.vitem &$recipients$& -.vindex "&$recipients$&" +.tvar &$recipients$& This variable contains a list of envelope recipients for a message. A comma and a space separate the addresses in the replacement text. However, the variable is not generally available, to prevent exposure of Bcc recipients in @@ -13404,10 +13512,12 @@ This variable is set to contain the matching regular expression after a When a &%regex%& or &%mime_regex%& ACL condition succeeds, these variables contain the captured substrings identified by the regular expression. +.new +If the subject string was tainted then so will any captured substring. +.wen -.vitem &$reply_address$& -.vindex "&$reply_address$&" +.tvar &$reply_address$& When a message is being processed, this variable contains the contents of the &'Reply-To:'& header line if one exists and it is not empty, or otherwise the contents of the &'From:'& header line. Apart from the removal of leading @@ -13456,8 +13566,7 @@ One of its values causes the address to be passed to another router. When this happens, &$self_hostname$& is set to the name of the local host that the original router encountered. In other circumstances its contents are null. -.vitem &$sender_address$& -.vindex "&$sender_address$&" +.tvar &$sender_address$& When a message is being processed, this variable contains the sender's address that was received in the message's envelope. The case of letters in the address is retained, in both the local part and the domain. For bounce messages, the @@ -13472,12 +13581,10 @@ distinguish it from data from a recipient address. The value does not persist after the end of the current ACL statement. If you want to preserve it for longer, you can save it in an ACL variable. -.vitem &$sender_address_domain$& -.vindex "&$sender_address_domain$&" +.tvar &$sender_address_domain$& The domain portion of &$sender_address$&. -.vitem &$sender_address_local_part$& -.vindex "&$sender_address_local_part$&" +.tvar &$sender_address_local_part$& The local part portion of &$sender_address$&. .vitem &$sender_data$& @@ -13515,8 +13622,7 @@ This boolean variable is true if a successful HELO verification was .cindex "DNS" "DNSSEC" done using DNS information the resolver library stated was authenticated data. -.vitem &$sender_helo_name$& -.vindex "&$sender_helo_name$&" +.tvar &$sender_helo_name$& When a message is received from a remote host that has issued a HELO or EHLO command, the argument of that command is placed in this variable. It is also set if HELO or EHLO is used when a message is received using SMTP locally via @@ -13573,8 +13679,7 @@ all EDNS0 options, then this will have no effect. OpenBSD's asr resolver is known to currently ignore EDNS0, documented in CAVEATS of asr_run(3). -.vitem &$sender_host_name$& -.vindex "&$sender_host_name$&" +.tvar &$sender_host_name$& When a message is received from a remote host, this variable contains the host's name as obtained by looking up its IP address. For messages received by other means, this variable is empty. @@ -13692,8 +13797,7 @@ host name, as specified by the &%smtp_active_hostname%& option. The value of &$smtp_active_hostname$& is saved with any message that is received, so its value can be consulted during routing and delivery. -.vitem &$smtp_command$& -.vindex "&$smtp_command$&" +.tvar &$smtp_command$& During the processing of an incoming SMTP command, this variable contains the entire command. This makes it possible to distinguish between HELO and EHLO in the HELO ACL, and also to distinguish between commands such as these: @@ -13706,9 +13810,8 @@ command, the address in &$smtp_command$& is the original address before any rewriting, whereas the values in &$local_part$& and &$domain$& are taken from the address after SMTP-time rewriting. -.vitem &$smtp_command_argument$& +.tvar &$smtp_command_argument$& .cindex "SMTP" "command, argument for" -.vindex "&$smtp_command_argument$&" While an ACL is running to check an SMTP command, this variable contains the argument, that is, the text that follows the command name, with leading white space removed. Following the introduction of &$smtp_command$&, this variable is @@ -13949,8 +14052,7 @@ which is not the leaf. Observability for TLS session resumption. See &<>& for details. -.vitem &$tls_in_sni$& -.vindex "&$tls_in_sni$&" +.tvar &$tls_in_sni$& .vindex "&$tls_sni$&" .cindex "TLS" "Server Name Indication" .cindex "TLS" SNI @@ -14569,7 +14671,6 @@ listed in more than one group. .section "Miscellaneous" "SECID96" .table2 .row &%add_environment%& "environment variables" -.row &%allow_insecure_tainted_data%& "turn taint errors into warnings" .row &%bi_command%& "to run for &%-bi%& command line option" .row &%debug_store%& "do extra internal checks" .row &%disable_ipv6%& "do no IPv6 processing" @@ -15183,17 +15284,6 @@ domains (defined in the named domain list &%local_domains%& in the default configuration). This &"magic string"& matches the domain literal form of all the local host's IP addresses. -.option allow_insecure_tainted_data main boolean false -.cindex "de-tainting" -.oindex "allow_insecure_tainted_data" -The handling of tainted data may break older (pre 4.94) configurations. -Setting this option to "true" turns taint errors (which result in a temporary -message rejection) into warnings. This option is meant as mitigation only -and deprecated already today. Future releases of Exim may ignore it. -The &%taint%& log selector can be used to suppress even the warnings. - - - .option allow_mx_to_ip main boolean false .cindex "MX record" "pointing to IP address" It appears that more and more DNS zone administrators are breaking the rules @@ -15854,8 +15944,8 @@ described in section &<>&. .cindex "ESMTP extensions" DSN DSN extensions (RFC3461) will be advertised in the EHLO message to, and accepted from, these hosts. -Hosts may use the NOTIFY and ENVID options on RCPT TO commands, -and RET and ORCPT options on MAIL FROM commands. +Hosts may use the NOTIFY and ORCPT options on RCPT TO commands, +and RET and ENVID options on MAIL FROM commands. A NOTIFY=SUCCESS option requests success-DSN messages. A NOTIFY= option with no argument requests that no delay or failure DSNs are sent. @@ -18410,12 +18500,7 @@ larger prime than requested. The value of this option is expanded and indicates the source of DH parameters to be used by Exim. -This option is ignored for GnuTLS version 3.6.0 and later. -The library manages parameter negotiation internally. - -&*Note: The Exim Maintainers strongly recommend, -for other TLS library versions, -using a filename with site-generated +&*Note: The Exim Maintainers strongly recommend using a filename with site-generated local DH parameters*&, which has been supported across all versions of Exim. The other specific constants available are a fallback so that even when "unconfigured", Exim can offer Perfect Forward Secrecy in older ciphersuites in TLS. @@ -18466,8 +18551,17 @@ of the later IKE values, which led into RFC7919 providing new fixed constants (the "ffdhe" identifiers). At this point, all of the "ike" values should be considered obsolete; -they're still in Exim to avoid breaking unusual configurations, but are +they are still in Exim to avoid breaking unusual configurations, but are candidates for removal the next time we have backwards-incompatible changes. +.new +Two of them in particular (&`ike1`& and &`ike22`&) are called out by RFC 8247 +as MUST NOT use for IPSEC, and two more (&`ike23`& and &`ike24`&) as +SHOULD NOT. +Because of this, Exim regards them as deprecated; if either of the first pair +are used, warnings will be logged in the paniclog, and if any are used then +warnings will be logged in the mainlog. +All four will be removed in a future Exim release. +.wen The TLS protocol does not negotiate an acceptable size for this; clients tend to hard-drop connections if what is offered by the server is unacceptable, @@ -18640,7 +18734,8 @@ either &%tls_verify_hosts%& or &%tls_try_verify_hosts%& is set and Any client that matches &%tls_verify_hosts%& is constrained by &%tls_verify_certificates%&. When the client initiates a TLS session, it must present one of the listed certificates. If it does not, the connection is -aborted. &*Warning*&: Including a host in &%tls_verify_hosts%& does not require +aborted. +&*Warning*&: Including a host in &%tls_verify_hosts%& does not require the host to use TLS. It can still send SMTP commands through unencrypted connections. Forcing a client to use TLS has to be done separately using an ACL to reject inappropriate commands when the connection is not encrypted. @@ -18944,6 +19039,7 @@ than trying to read &_/etc/passwd_& directly. This means that other methods of holding password data (such as NIS) are supported. If the local part is a local user, .cindex "tainted data" "de-tainting" +.cindex "de-tainting" "using router check_local_user option" &$local_part_data$& is set to an untainted version of the local part and &$home$& is set from the password data. The latter can be tested in other preconditions that are evaluated after this one (the order of evaluation is @@ -22777,9 +22873,10 @@ an ideal name for this feature here, but as it was already implemented for the The expansion variables &$host$& and &$host_address$& are available when the transport is a remote one. They contain the name and IP address of the host to which the message is being sent. For example: +. used to have $sender_address in this cmdline, but it's tainted .code transport_filter = /some/directory/transport-filter.pl \ - $host $host_address $sender_address $pipe_addresses + $host $host_address $pipe_addresses .endd Two problems arise if you want to use more complicated expansion items to @@ -23215,6 +23312,7 @@ The value is used for checking instead of a home directory; checking is done in "belowhome" mode. .cindex "tainted data" "de-tainting" +.cindex "de-tainting" "using appendfile create_file option" If "belowhome" checking is used, the file or directory path becomes de-tainted. @@ -24650,6 +24748,11 @@ This list is a compromise for maximum compatibility with other MTAs. Note that the &%environment%& option can be used to add additional variables to this environment. The environment for the &(pipe)& transport is not subject to the &%add_environment%& and &%keep_environment%& main config options. +.new +&*Note*&: Using enviroment variables loses track of tainted data. +Writers of &(pipe)& transport commands should be wary of data supplied +by potential attackers. +.wen .display &`DOMAIN `& the domain of the address &`HOME `& the home directory, if set @@ -24741,6 +24844,11 @@ the &%path%& option below). The command is split up into separate arguments by Exim, and each argument is separately expanded, as described in section &<>& above. +.new +.cindex "tainted data" +No part of the resulting command may be tainted. +.wen + .option environment pipe string&!! unset .cindex "&(pipe)& transport" "environment for command" @@ -25056,12 +25164,15 @@ use a shell to run pipe commands. .cindex "Cyrus" The next example shows a transport and a router for a system where local deliveries are handled by the Cyrus IMAP server. +. Used to have R: local_part_suffix = .* + T: -m $local_part_suffix_v +. but that suffix is tainted so cannot be used in a command arg +. Really, you'd want to use a lookup for acceptable suffixes to do real detainting .code # transport local_delivery_cyrus: driver = pipe command = /usr/cyrus/bin/deliver \ - -m ${substr_1:$local_part_suffix} -- $local_part + -- $local_part_data user = cyrus group = mail return_output @@ -25073,7 +25184,6 @@ local_delivery_cyrus: local_user_cyrus: driver = accept check_local_user - local_part_suffix = .* transport = local_delivery_cyrus .endd Note the unsetting of &%message_prefix%& and &%message_suffix%&, and the use of @@ -25439,12 +25549,45 @@ servers or different local IP addresses. For example, if you want the string that is used for &%helo_data%& to be obtained by a DNS lookup of the outgoing interface address, you could use this: .code -helo_data = ${lookup dnsdb{ptr=$sending_ip_address}{$value}\ +helo_data = ${lookup dnsdb{ptr=$sending_ip_address} \ + {${listextract{1}{<\n $value}}} \ {$primary_hostname}} .endd The use of &%helo_data%& applies both to sending messages and when doing callouts. +.new +.option host_name_extract smtp "string list&!!" "see below" +.cindex "load balancer" "hosts behind" +.cindex TLS resumption +Some mail-accepting sites +(notably Microsoft) +operate many servers behind a network load-balancer. When this is done, +with separated TLS session caches, TLS session resuption becomes problematic. +It will only succeed when the same server happens to be selected by the +load-balancer, matching the session stored in the client's cache. + +Exim can pull out a server name, if there is one, from the response to the +client's SMTP EHLO command. +The default value of this option: +.code + ${if and { {match {$host} {.outlook.com\$}} \ + {match {$item} {\N^250-([\w.]+)\s\N}} \ + } {$1}} +.endd +suffices for one known case. +During the expansion of this option the &$item$& variable will have the +server's EHLO response. +The result of the option expansion is included in the key used to store and +retrieve the TLS session, for session resumption. + +Operators of high-load sites may wish to evaluate their logs for indications +of other destination sites operating load-balancers, and develop a suitable +expression for this option. +The smtp:ehlo event and the &$tls_out_resumption$& variable +will be useful for such work. +.wen + .option hosts smtp "string list&!!" unset Hosts are associated with an address by a router such as &(dnslookup)&, which finds the hosts by looking up the address domain in the DNS, or by @@ -25512,7 +25655,10 @@ so combines well with TCP Fast Open. See also the &%pipelining_connect_advertise_hosts%& main option. Note: -When the facility is used, the transport &%helo_data%& option +.new +When the facility is used, if the transport &%interface%& option is unset +the &%helo_data%& option +.wen will be expanded before the &$sending_ip_address$& variable is filled in. A check is made for the use of that variable, without the @@ -26095,6 +26241,10 @@ certificate verification must succeed. The &%tls_verify_certificates%& option must also be set. If both this option and &%tls_try_verify_hosts%& are unset operation is as if this option selected all hosts. +&*Warning*&: Including a host in &%tls_verify_hosts%& does not require +that connections use TLS. +Fallback to in-clear communication will be done unless restricted by +the &%hosts_require_tls%& option. .option utf8_downconvert smtp integer&!! -1 .cindex utf8 "address downconversion" @@ -29784,8 +29934,10 @@ nothing more to it. Choosing a sensible value not derived insecurely is the only point of caution. The &$tls_out_sni$& variable will be set to this string for the lifetime of the client connection (including during authentication). +.new If DANE validated the connection attempt then the value of the &%tls_sni%& option -is forced to the domain part of the recipient address. +is forced to the name of the destination host, after any MX- or CNAME-following. +.wen Except during SMTP client sessions, if &$tls_in_sni$& is set then it is a string received from a client. @@ -30440,6 +30592,11 @@ accepted by an &%accept%& verb that has a &%message%& modifier, the contents of the message override the banner message that is otherwise specified by the &%smtp_banner%& option. +.new +For tls-on-connect connections, the ACL is run after the TLS connection +is accepted (however, &%host_reject_connection%& is tested before). +.wen + .section "The EHLO/HELO ACL" "SECID192" .cindex "EHLO" "ACL for" @@ -31557,12 +31714,43 @@ sender when the destination system is doing content-scan based rejection. This control turns on debug logging, almost as though Exim had been invoked with &`-d`&, with the output going to a new logfile in the usual logs directory, by default called &'debuglog'&. -The filename can be adjusted with the &'tag'& option, which -may access any variables already defined. The logging may be adjusted with -the &'opts'& option, which takes the same values as the &`-d`& command-line -option. -Logging started this way may be stopped, and the file removed, -with the &'kill'& option. + +.new +Options are a slash-separated list. +If an option takes an argument, the option name and argument are separated by +an equals character. +Several options are supported: +.wen +.display +tag=<&'suffix'&> The filename can be adjusted with thise option. + The argument, which may access any variables already defined, + is appended to the default name. + +opts=<&'debug&~options'&> The argument specififes what is to be logged, + using the same values as the &`-d`& command-line option. + +stop Logging started with this control may be + stopped by using this option. + +kill Logging started with this control may be + stopped by using this option. + Additionally the debug file will be removed, + providing one means for speculative debug tracing. + +pretrigger=<&'size'&> This option specifies a memory buffuer to be used + for pre-trigger debug capture. + Debug lines are recorded in the buffer until + and if) a trigger occurs; at which time they are + dumped to the debug file. Newer lines displace the + oldest if the buffer is full. After a trigger, + immediate writes to file are done as normal. + +trigger=<&'reason'&> This option selects cause for the pretrigger buffer + see above) to be copied to file. A reason of $*now* + take effect immediately; one of &*paniclog*& triggers + on a write to the panic log. +.endd + Some examples (which depend on variables that don't exist in all contexts): .code @@ -31571,6 +31759,8 @@ contexts): control = debug/opts=+expand+acl control = debug/tag=.$message_exim_id/opts=+expand control = debug/kill + control = debug/opts=+all/pretrigger=1024/trigger=paniclog + control = debug/trigger=now .endd @@ -32941,7 +33131,7 @@ situation has been previously met. It uses a hints database to record a timestamp against a key. host. The syntax of the condition is: .display -&`seen =`& <&'time interval'&> &`/`& <&'options'&> +&`seen =`& <&'optional flag'&><&'time interval'&> &`/`& <&'options'&> .endd For example, @@ -32950,8 +33140,10 @@ defer seen = -5m / key=${sender_host_address}_$local_part@$domain .endd in a RCPT ACL will implement simple greylisting. -The parameters for the condition -are an interval followed, slash-separated, by a list of options. +The parameters for the condition are +a possible minus sign, +then an interval, +then, slash-separated, a list of options. The interval is taken as an offset before the current time, and used for the test. If the interval is preceded by a minus sign then the condition returns @@ -32969,6 +33161,8 @@ no record create or update is done. If a &%write%& option is given then a record create or update is always done. An update is done if the test is for &"since"&. +If none of those hold and there was no existing record, +a record is created. Creates and updates are marked with the current time. @@ -38814,7 +39008,6 @@ selection marked by asterisks: &` smtp_protocol_error `& SMTP protocol errors &` smtp_syntax_error `& SMTP syntax errors &` subject `& contents of &'Subject:'& on <= lines -&`*taint `& taint errors or warnings &`*tls_certificate_verified `& certificate verification status &`*tls_cipher `& TLS cipher suite on <= and => lines &` tls_peerdn `& TLS peer DN on <= and => lines @@ -39208,11 +39401,6 @@ using a CA trust anchor, &`CV=dane`& if using a DNS trust anchor, and &`CV=no`& if not. .next -.cindex "log" "Taint warnings" -&%taint%&: Log warnings about tainted data. This selector can't be -turned of if &%allow_insecure_tainted_data%& is false (which is the -default). -.next .cindex "log" "TLS cipher" .cindex "TLS" "logging cipher" &%tls_cipher%&: When a message is sent or received over an encrypted @@ -39357,9 +39545,6 @@ or (in case &*-a*& switch is specified) .code exim -bp .endd -The &*-C*& option is used to specify an alternate &_exim.conf_& which might -contain alternate exim configuration the queue management might be using. - to obtain a queue listing, and then greps the output to select messages that match given criteria. The following selection options are available: @@ -39416,7 +39601,22 @@ Display messages in reverse order. Include delivered recipients in queue listing. .endlist +The following options give alternates for configuration: + +.vlist +.vitem &*-C*&&~<&'config&~file'&> +is used to specify an alternate &_exim.conf_& which might +contain alternate exim configuration the queue management might be using. + +.vitem &*-E*&&~<&'path'&> +can be used to specify a path for the exim binary, +overriding the built-in one. +.endlist + There is one more option, &%-h%&, which outputs a list of options. +.new +At least one selection option, or either the &*-c*& or &*-h*& option, must be given. +.wen @@ -39801,14 +40001,16 @@ The entire contents of a database are written to the standard output by the &'exim_dumpdb'& program, .new taking as arguments the spool and database names. -An option &'-z'& may be given to regest times in UTC; +An option &'-z'& may be given to request times in UTC; otherwise times are in the local timezone. +An option &'-k'& may be given to dump only the record keys. .wen For example, to dump the retry database: .code exim_dumpdb /var/spool/exim retry .endd -Two lines of output are produced for each entry: +For the retry database +two lines of output are produced for each entry: .code T:mail.ref.example:192.168.242.242 146 77 Connection refused 31-Oct-1995 12:00:12 02-Nov-1995 12:21:39 02-Nov-1995 20:21:39 * @@ -40683,7 +40885,7 @@ Consider the use of the &%inlisti%& expansion condition instead. .cindex "security" "data sources" .cindex "security" "regular expressions" .cindex "regular expressions" "security" -.cindex "PCRE" "security" +.cindex "PCRE2" "security" If configuration data for Exim can come from untrustworthy sources, there are some issues to be aware of: @@ -40693,7 +40895,7 @@ Use of &%${expand...}%& may provide a path for shell injection attacks. Letting untrusted data provide a regular expression is unwise. .next Using &%${match...}%& to apply a fixed regular expression against untrusted -data may result in pathological behaviour within PCRE. Be aware of what +data may result in pathological behaviour within PCRE2. Be aware of what "backtracking" means and consider options for being more strict with a regular expression. Avenues to explore include limiting what can match (avoiding &`.`& when &`[a-z0-9]`& or other character class will do), use of atomic grouping and @@ -40934,8 +41136,18 @@ was received, in the conventional Unix form &-- the number of seconds since the start of the epoch. The second number is a count of the number of messages warning of delayed delivery that have been sent to the sender. -There follow a number of lines starting with a hyphen. These can appear in any -order, and are omitted when not relevant: +.new +There follow a number of lines starting with a hyphen. +These contain variables, can appear in any +order, and are omitted when not relevant. + +If there is a second hyphen after the first, +the corresponding data is tainted. +If there is a value in parentheses, the data is quoted for a lookup. + +The following word specifies a variable, +and the remainder of the item depends on the variable. +.wen .vlist .vitem "&%-acl%&&~<&'number'&>&~<&'length'&>" @@ -41091,9 +41303,6 @@ was received from the client, this records the Distinguished Name from that certificate. .endlist -Any of the above may have an extra hyphen prepended, to indicate the the -corresponding data is untrusted. - Following the options there is a list of those addresses to which the message is not to be delivered. This set of addresses is initialized from the command line when the &%-t%& option is used and &%extract_addresses_remove_arguments%& @@ -42574,6 +42783,7 @@ Events have names which correspond to the point in process at which they fire. The name is placed in the variable &$event_name$& and the event action expansion must check this, as it will be called for every possible event type. +.new The current list of events is: .display &`dane:fail after transport `& per connection @@ -42588,9 +42798,11 @@ The current list of events is: &`tcp:connect before transport `& per connection &`tcp:close after transport `& per connection &`tls:cert before both `& per certificate in verification chain +&`tls:fail:connect after main `& per connection &`smtp:connect after transport `& per connection &`smtp:ehlo after transport `& per connection .endd +.wen New event types may be added in future. The event name is a colon-separated list, defining the type of @@ -42616,6 +42828,7 @@ with the event type: &`msg:rcpt:host:defer `& error string &`msg:rcpt:defer `& error string &`tls:cert `& verification chain depth +&`tls:fail:connect `& error string &`smtp:connect `& smtp banner &`smtp:ehlo `& smtp ehlo response .endd