diff options
Diffstat (limited to 'debian/debconf/conf.d/acl/30_exim4-config_check_rcpt')
| -rw-r--r-- | debian/debconf/conf.d/acl/30_exim4-config_check_rcpt | 358 |
1 files changed, 358 insertions, 0 deletions
diff --git a/debian/debconf/conf.d/acl/30_exim4-config_check_rcpt b/debian/debconf/conf.d/acl/30_exim4-config_check_rcpt new file mode 100644 index 0000000..0403165 --- /dev/null +++ b/debian/debconf/conf.d/acl/30_exim4-config_check_rcpt @@ -0,0 +1,358 @@ + +### acl/30_exim4-config_check_rcpt +################################# + +# define macros to be used below in this file to check recipient +# local parts for strange characters. Documentation below. +# This blocks local parts that begin with a dot or contain a quite +# broad range of non-alphanumeric characters. + +.ifndef CHECK_RCPT_LOCAL_LOCALPARTS +CHECK_RCPT_LOCAL_LOCALPARTS = ^[.] : ^.*[@%!/|`#&?] +.endif + +.ifndef CHECK_RCPT_REMOTE_LOCALPARTS +CHECK_RCPT_REMOTE_LOCALPARTS = ^[./|] : ^.*[@%!`#&?] : ^.*/\\.\\./ +.endif + +# This access control list is used for every RCPT command in an incoming +# SMTP message. The tests are run in order until the address is either +# accepted or denied. +# +acl_check_rcpt: + + # Accept if the source is local SMTP (i.e. not over TCP/IP). We do this by + # testing for an empty sending host field. + accept + hosts = : + control = dkim_disable_verify + + # Do not try to verify DKIM signatures of incoming mail if DC_minimaldns + # or DISABLE_DKIM_VERIFY are set. +.ifdef DC_minimaldns + warn + control = dkim_disable_verify +.else +.ifdef DISABLE_DKIM_VERIFY + warn + control = dkim_disable_verify +.endif +.endif + + # The following section of the ACL is concerned with local parts that contain + # certain non-alphanumeric characters. Dots in unusual places are + # handled by this ACL as well. + # + # Non-alphanumeric characters other than dots are rarely found in genuine + # local parts, but are often tried by people looking to circumvent + # relaying restrictions. Therefore, although they are valid in local + # parts, these rules disallow certain non-alphanumeric characters, as + # a precaution. + # + # Empty components (two dots in a row) are not valid in RFC 2822, but Exim + # allows them because they have been encountered. (Consider local parts + # constructed as "firstinitial.secondinitial.familyname" when applied to + # a name without a second initial.) However, a local part starting + # with a dot or containing /../ can cause trouble if it is used as part of a + # file name (e.g. for a mailing list). This is also true for local parts that + # contain slashes. A pipe symbol can also be troublesome if the local part is + # incorporated unthinkingly into a shell command line. + # + # These ACL components will block recipient addresses that are valid + # from an RFC5322 point of view. We chose to have them blocked by + # default for security reasons. + # + # If you feel that your site should have less strict recipient + # checking, please feel free to change the default values of the macros + # defined in main/01_exim4-config_listmacrosdefs or override them from a + # local configuration file. + # + # Two different rules are used. The first one has a quite strict + # default, and is applied to messages that are addressed to one of the + # local domains handled by this host. + + # The default value of CHECK_RCPT_LOCAL_LOCALPARTS is defined + # at the top of this file. + .ifdef CHECK_RCPT_LOCAL_LOCALPARTS + deny + domains = +local_domains + local_parts = CHECK_RCPT_LOCAL_LOCALPARTS + message = restricted characters in address + .endif + + + # The second rule applies to all other domains, and its default is + # considerably less strict. + + # The default value of CHECK_RCPT_REMOTE_LOCALPARTS is defined in + # main/01_exim4-config_listmacrosdefs: + # CHECK_RCPT_REMOTE_LOCALPARTS = ^[./|] : ^.*[@%!`#&?] : ^.*/\\.\\./ + + # It allows local users to send outgoing messages to sites + # that use slashes and vertical bars in their local parts. It blocks + # local parts that begin with a dot, slash, or vertical bar, but allows + # these characters within the local part. However, the sequence /../ is + # barred. The use of some other non-alphanumeric characters is blocked. + # Single quotes might probably be dangerous as well, but they're + # allowed by the default regexps to avoid rejecting mails to Ireland. + # The motivation here is to prevent local users (or local users' malware) + # from mounting certain kinds of attack on remote sites. + .ifdef CHECK_RCPT_REMOTE_LOCALPARTS + deny + domains = !+local_domains + local_parts = CHECK_RCPT_REMOTE_LOCALPARTS + message = restricted characters in address + .endif + + + # Accept mail to postmaster in any local domain, regardless of the source, + # and without verifying the sender. + # + accept + .ifndef CHECK_RCPT_POSTMASTER + local_parts = postmaster + .else + local_parts = CHECK_RCPT_POSTMASTER + .endif + domains = +local_domains : +relay_to_domains + + + # Deny unless the sender address can be verified. + # + # This is disabled by default so that DNSless systems don't break. If + # your system can do DNS lookups without delay or cost, you might want + # to enable this feature. + # + # This feature does not work in smarthost and satellite setups as + # with these setups all domains pass verification. See spec.txt section + # "Access control lists" subsection "Address verification" with the added + # information that a smarthost/satellite setup routes all non-local e-mail + # to the smarthost. + .ifdef CHECK_RCPT_VERIFY_SENDER + deny + !acl = acl_local_deny_exceptions + !verify = sender + message = Sender verification failed + .endif + + # Verify senders listed in local_sender_callout with a callout. + # + # In smarthost and satellite setups, this causes the callout to be + # done to the smarthost. Verification will thus only be reliable if the + # smarthost does reject illegal addresses in the SMTP dialog. + deny + !acl = acl_local_deny_exceptions + senders = ${if exists{CONFDIR/local_sender_callout}\ + {CONFDIR/local_sender_callout}\ + {}} + !verify = sender/callout + + .ifndef CHECK_RCPT_NO_FAIL_TOO_MANY_BAD_RCPT + # Reject all RCPT commands after too many bad recipients + # This is partly a defense against spam abuse and partly attacker abuse. + # Real senders should manage, by the time they get to 10 RCPT directives, + # to have had at least half of them be real addresses. + # + # This is a lightweight check and can protect you against repeated + # invocations of more heavy-weight checks which would come after it. + + deny condition = ${if and {\ + {>{$rcpt_count}{10}}\ + {<{$recipients_count}{${eval:$rcpt_count/2}}} }} + message = Rejected for too many bad recipients + logwrite = REJECT [$sender_host_address]: bad recipient count high [${eval:$rcpt_count-$recipients_count}] + .endif + + # Accept if the message comes from one of the hosts for which we are an + # outgoing relay. It is assumed that such hosts are most likely to be MUAs, + # so we set control=submission to make Exim treat the message as a + # submission. It will fix up various errors in the message, for example, the + # lack of a Date: header line. If you are actually relaying out out from + # MTAs, you may want to disable this. If you are handling both relaying from + # MTAs and submissions from MUAs you should probably split them into two + # lists, and handle them differently. + + # Recipient verification is omitted here, because in many cases the clients + # are dumb MUAs that don't cope well with SMTP error responses. If you are + # actually relaying out from MTAs, you should probably add recipient + # verification here. + + # Note that, by putting this test before any DNS black list checks, you will + # always accept from these hosts, even if they end up on a black list. The + # assumption is that they are your friends, and if they get onto black + # list, it is a mistake. + accept + hosts = +relay_from_hosts + control = submission/sender_retain + control = dkim_disable_verify + + + # Accept if the message arrived over an authenticated connection, from + # any host. Again, these messages are usually from MUAs, so recipient + # verification is omitted, and submission mode is set. And again, we do this + # check before any black list tests. + accept + authenticated = * + control = submission/sender_retain + control = dkim_disable_verify + + # Insist that any other recipient address that we accept is either in one of + # our local domains, or is in a domain for which we explicitly allow + # relaying. Any other domain is rejected as being unacceptable for relaying. + require + message = relay not permitted + domains = +local_domains : +relay_to_domains + + + # We also require all accepted addresses to be verifiable. This check will + # do local part verification for local domains, but only check the domain + # for remote domains. + require + verify = recipient + + + # Verify recipients listed in local_rcpt_callout with a callout. + # This is especially handy for forwarding MX hosts (secondary MX or + # mail hubs) of domains that receive a lot of spam to non-existent + # addresses. The only way to check local parts for remote relay + # domains is to use a callout (add /callout), but please read the + # documentation about callouts before doing this. + deny + !acl = acl_local_deny_exceptions + recipients = ${if exists{CONFDIR/local_rcpt_callout}\ + {CONFDIR/local_rcpt_callout}\ + {}} + !verify = recipient/callout + + + # CONFDIR/local_sender_blacklist holds a list of envelope senders that + # should have their access denied to the local host. Incoming messages + # with one of these senders are rejected at RCPT time. + # + # The explicit white lists are honored as well as negative items in + # the black list. See exim4-config_files(5) for details. + deny + !acl = acl_local_deny_exceptions + senders = ${if exists{CONFDIR/local_sender_blacklist}\ + {CONFDIR/local_sender_blacklist}\ + {}} + message = sender envelope address $sender_address is locally blacklisted here. If you think this is wrong, get in touch with postmaster + log_message = sender envelope address is locally blacklisted. + + + # deny bad sites (IP address) + # CONFDIR/local_host_blacklist holds a list of host names, IP addresses + # and networks (CIDR notation) that should have their access denied to + # The local host. Messages coming in from a listed host will have all + # RCPT statements rejected. + # + # The explicit white lists are honored as well as negative items in + # the black list. See exim4-config_files(5) for details. + deny + !acl = acl_local_deny_exceptions + hosts = ${if exists{CONFDIR/local_host_blacklist}\ + {CONFDIR/local_host_blacklist}\ + {}} + message = sender IP address $sender_host_address is locally blacklisted here. If you think this is wrong, get in touch with postmaster + log_message = sender IP address is locally blacklisted. + + + # Warn if the sender host does not have valid reverse DNS. + # + # If your system can do DNS lookups without delay or cost, you might want + # to enable this. + # If sender_host_address is defined, it's a remote call. If + # sender_host_name is not defined, then reverse lookup failed. Use + # this instead of !verify = reverse_host_lookup to catch deferrals + # as well as outright failures. + .ifdef CHECK_RCPT_REVERSE_DNS + warn + condition = ${if and{{def:sender_host_address}{!def:sender_host_name}}\ + {yes}{no}} + add_header = X-Host-Lookup-Failed: Reverse DNS lookup failed for $sender_host_address (${if eq{$host_lookup_failed}{1}{failed}{deferred}}) + .endif + + + .ifdef CHECK_RCPT_SPF + .ifdef _HAVE_SPF + deny + !acl = acl_local_deny_exceptions + spf = fail + message = [SPF] $sender_host_address is not allowed to send mail from \ + ${if def:sender_address_domain {$sender_address_domain}{$sender_helo_name}}. + log_message = SPF check failed. + + defer + !acl = acl_local_deny_exceptions + spf = temperror + message = Temporary DNS error while checking SPF record. Try again later. + + warn + spf = pass:softfail:neutral:permerror + add_header = :at_start:$spf_received + .endif + .endif + + + # Check against classic DNS "black" lists (DNSBLs) which list + # sender IP addresses + .ifdef CHECK_RCPT_IP_DNSBLS + warn + dnslists = CHECK_RCPT_IP_DNSBLS + add_header = X-Warning: $sender_host_address is listed at $dnslist_domain ($dnslist_value: $dnslist_text) + log_message = $sender_host_address is listed at $dnslist_domain ($dnslist_value: $dnslist_text) + .endif + + + # Check against DNSBLs which list sender domains, with an option to locally + # whitelist certain domains that might be blacklisted. + # + # Note: If you define CHECK_RCPT_DOMAIN_DNSBLS, you must append + # "/$sender_address_domain" after each domain. For example: + # CHECK_RCPT_DOMAIN_DNSBLS = rhsbl.foo.org/$sender_address_domain \ + # : rhsbl.bar.org/$sender_address_domain + .ifdef CHECK_RCPT_DOMAIN_DNSBLS + warn + !senders = ${if exists{CONFDIR/local_domain_dnsbl_whitelist}\ + {CONFDIR/local_domain_dnsbl_whitelist}\ + {}} + dnslists = CHECK_RCPT_DOMAIN_DNSBLS + add_header = X-Warning: $sender_address_domain is listed at $dnslist_domain ($dnslist_value: $dnslist_text) + log_message = $sender_address_domain is listed at $dnslist_domain ($dnslist_value: $dnslist_text) + .endif + + + # This hook allows you to hook in your own ACLs without having to + # modify this file. If you do it like we suggest, you'll end up with + # a small performance penalty since there is an additional file being + # accessed. This doesn't happen if you leave the macro unset. + .ifdef CHECK_RCPT_LOCAL_ACL_FILE + .include CHECK_RCPT_LOCAL_ACL_FILE + .endif + + + ############################################################################# + # This check is commented out because it is recognized that not every + # sysadmin will want to do it. If you enable it, the check performs + # Client SMTP Authorization (csa) checks on the sending host. These checks + # do DNS lookups for SRV records. The CSA proposal is currently (May 2005) + # an Internet draft. You can, of course, add additional conditions to this + # ACL statement to restrict the CSA checks to certain hosts only. + # + # require verify = csa + ############################################################################# + + + # Accept if the address is in a domain for which we are an incoming relay, + # but again, only if the recipient can be verified. + + accept + domains = +relay_to_domains + endpass + verify = recipient + + + # At this point, the address has passed all the checks that have been + # configured, so we accept it unconditionally. + + accept |