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dmarc: added relaxed alignment tests

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Matt Simerson 2013-04-21 02:49:39 -04:00
parent 610c39dc74
commit 091843927d
1 changed files with 103 additions and 67 deletions
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170
plugins/dmarc
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@ -40,16 +40,12 @@ See Section 10 of the draft: Domain Owner Actions
pct=50; (percent of messages to filter)
=head2
=head1 DRAFT
http://www.dmarc.org/draft-dmarc-base-00-02.txt
=head1 TODO
1. run dmarc before SPF, if DMARC policy is discovered, ignore SPF
2. provide dmarc feedback to domains that request it
3. If a message has multiple 'From' recipients, reject it
@ -58,7 +54,7 @@ http://www.dmarc.org/draft-dmarc-base-00-02.txt
=head1 IMPLEMENTATION
1. Primary identifier is RFC5322.From field
1. Primary identifier is RFC5322.From field (From: header)
2. Senders can specify strict or relaxed mode
@ -72,29 +68,6 @@ http://www.dmarc.org/draft-dmarc-base-00-02.txt
RFC5322.From purports to be from a domain that appears to be
either non-existent or incapable of receiving mail.
=head2 Reports should include
The report SHOULD include the following data:
o Enough information for the report consumer to re-calculate DMARC
disposition based on the published policy, message dispositon, and
SPF, DKIM, and identifier alignment results. {R12}
o Data for each sender subdomain separately from mail from the
sender's organizational domain, even if no subdomain policy is
applied. {R13}
o Sending and receiving domains {R17}
o The policy requested by the Domain Owner and the policy actually
applied (if different) {R18}
o The number of successful authentications {R19}
o The counts of messages based on all messages received even if
their delivery is ultimately blocked by other filtering agents
{R20}
=cut
use strict;
@ -123,15 +96,13 @@ sub data_post_handler {
# 11.1. Extract Author Domain
# TODO: check exists_in_dns result, and possibly reject here if domain non-exist
my $from_host = $self->get_from_host($transaction) or return DECLINED;
if (!$self->exists_in_dns($from_host)) {
my $org_host = $self->get_organizational_domain($from_host);
if (!$self->exists_in_dns($org_host)) {
$self->log(LOGINFO, "fail, domain/org not in DNS");
my $org_host = $self->get_organizational_domain($from_host);
#return $self->get_reject();
return DECLINED;
if (!$self->exists_in_dns($from_host)) {
if (!$self->exists_in_dns($org_host)) {
$self->log(LOGINFO, "fail, $from_host not in DNS");
return $self->get_reject("RFC5322.From host does not exist");
}
}
@ -140,18 +111,30 @@ sub data_post_handler {
or return DECLINED;
# 3. Perform DKIM signature verification checks. A single email may
# contain multiple DKIM signatures. The results of this step are
# passed to the remainder of the algorithm and MUST include the
# value of the "d=" tag from all DKIM signatures that successfully
# validated.
my $dkim_sigs = $self->connection->notes('dkim_pass_domains') || [];
# contain multiple DKIM signatures. The results MUST include the
# value of the "d=" tag from all DKIM signatures that validated.
#my $dkim_sigs = $self->connection->notes('dkim_pass_domains') || [];
# 4. Perform SPF validation checks. The results of this step are
# passed to the remainder of the algorithm and MUST include the
# domain name from the RFC5321.MailFrom if SPF evaluation returned
# a "pass" result.
# 4. Perform SPF validation checks. The results of this step
# MUST include the domain name from the RFC5321.MailFrom if SPF
# evaluation returned a "pass" result.
my $spf_dom = $transaction->notes('spf_pass_host');
# 5. Conduct identifier alignment checks.
return DECLINED
if $self->is_aligned($from_host, $org_host, $policy, $spf_dom );
# 6. Apply policy. Emails that fail the DMARC mechanism check are
# disposed of in accordance with the discovered DMARC policy of the
# Domain Owner. See Section 6.2 for details.
return DECLINED if lc $policy->{p} eq 'none';
return $self->get_reject("failed DMARC policy");
}
sub is_aligned {
my ($self, $from_host, $org_host, $policy, $spf_dom) = @_;
# 5. Conduct identifier alignment checks. With authentication checks
# and policy discovery performed, the Mail Receiver checks if
# Authenticated Identifiers fall into alignment as decribed in
@ -160,34 +143,43 @@ sub data_post_handler {
# the DMARC mechanism check. All other conditions (authentication
# failures, identifier mismatches) are considered to be DMARC
# mechanism check failures.
my $dkim_sigs = $self->connection->notes('dkim_pass_domains') || [];
foreach (@$dkim_sigs) {
if ($_ eq $from_host) { # strict alignment
$self->log(LOGINFO, "pass, DKIM alignment");
$self->adjust_karma(2); # big karma boost
return DECLINED;
if ($_ eq $from_host) { # strict alignment
$self->log(LOGINFO, "pass, DKIM aligned");
$self->adjust_karma(1);
return 1;
}
next if $policy->{adkim} && lc $policy->{adkim} eq 's'; # strict pol.
# default policy is relaxed
if ( $_ eq $org_host ) {
$self->log(LOGINFO, "pass, DKIM aligned, relaxed");
$self->adjust_karma(1);
return 1;
};
}
if ($spf_dom && $spf_dom eq $from_host) {
$self->adjust_karma(2); # big karma boost
$self->log(LOGINFO, "pass, SPF alignment");
return DECLINED;
return 0 if ! $spf_dom;
if ($spf_dom eq $from_host) {
$self->adjust_karma(1);
$self->log(LOGINFO, "pass, SPF aligned");
return 1;
}
return 0 if ($policy->{aspf} && lc $policy->{aspf} eq 's' ); # strict pol
if ($spf_dom eq $org_host) {
$self->adjust_karma(1);
$self->log(LOGINFO, "pass, SPF aligned, relaxed");
return 1;
}
# 6. Apply policy. Emails that fail the DMARC mechanism check are
# disposed of in accordance with the discovered DMARC policy of the
# Domain Owner. See Section 6.2 for details.
$self->log(LOGINFO, "skip, NEED RELAXED alignment");
return DECLINED;
}
return 0;
};
sub discover_policy {
my ($self, $from_host) = @_;
# 1. Mail Receivers MUST query the DNS for a DMARC TXT record at the
# DNS domain matching the one found in the RFC5322.From domain in
# the message. A possibly empty set of records is returned.
# 1. Mail Receivers MUST query the DNS for a DMARC TXT record...
my @matches = $self->fetch_dmarc_record($from_host); # 2. within
if (0 == scalar @matches) {
@ -304,29 +296,45 @@ sub get_organizational_domain {
sub exists_in_dns {
my ($self, $domain) = @_;
# the DMARC draft suggests rejecting messages whose From: domain does not
# exist in DNS. That's as far as it goes. So I went back to the ADSP (from
# where DMARC this originated, which in turn led me to the ietf-dkim email
# list where a handful of 'experts' failed to agree on The Right Way to
# perform this test. And thus no direction was given.
# As they point out:
# MX records aren't mandatory.
# A or AAAA records as fallback aren't reliable either.
# I chose to query the name and match NS,MX,A,or AAAA records. Since it gets
# repeated for the for the Organizational Name, if it fails, there's no
# delegation from the TLD.
my $res = $self->init_resolver();
my $query = $res->send($domain, 'NS') or do {
my $query = $res->send($domain) or do {
if ($res->errorstring eq 'NXDOMAIN') {
$self->log(LOGDEBUG, "fail, non-existent domain: $domain");
return;
}
$self->log(LOGINFO,
"error, looking up NS for $domain: " . $res->errorstring);
$self->log(LOGINFO, "error, looking up $domain: " . $res->errorstring);
return;
};
my @matches;
for my $rr ($query->answer) {
next if $rr->type ne 'NS';
next if $rr->type !~ /(?:NS|MX|A|AAAA)/;
push @matches, $rr->nsdname;
}
if (0 == scalar @matches) {
$self->log(LOGDEBUG, "fail, zero NS for $domain");
$self->log(LOGDEBUG, "fail, no records for $domain");
}
return @matches;
}
sub fetch_dmarc_record {
my ($self, $zone) = @_;
# 1. Mail Receivers MUST query the DNS for a DMARC TXT record at the
# DNS domain matching the one found in the RFC5322.From domain in
# the message. A possibly empty set of records is returned.
my $res = $self->init_resolver();
my $query = $res->send('_dmarc.' . $zone, 'TXT');
my @matches;
@ -366,6 +374,34 @@ sub parse_policy {
return %dmarc;
}
sub external_report {
=pod
The report SHOULD include the following data:
o Enough information for the report consumer to re-calculate DMARC
disposition based on the published policy, message dispositon, and
SPF, DKIM, and identifier alignment results. {R12}
o Data for each sender subdomain separately from mail from the
sender's organizational domain, even if no subdomain policy is
applied. {R13}
o Sending and receiving domains {R17}
o The policy requested by the Domain Owner and the policy actually
applied (if different) {R18}
o The number of successful authentications {R19}
o The counts of messages based on all messages received even if
their delivery is ultimately blocked by other filtering agents {R20}
=cut
};
sub verify_external_reporting {
=head2 Verify External Destinations