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dmarc: added subdomain policy handling

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This commit is contained in:
Matt Simerson 2013-04-25 02:25:21 -04:00
parent 9e204aaf7e
commit f854736142
1 changed files with 75 additions and 89 deletions
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156
plugins/dmarc
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@ -31,7 +31,7 @@ See Section 10 of the draft: Domain Owner Actions
=head3 Publish a DMARC policy =head3 Publish a DMARC policy
_dmarc IN TXT "v=DMARC1; p=reject; pct=100; rua=mailto:dmarc-feedback@example.com;" _dmarc IN TXT "v=DMARC1; p=reject; rua=mailto:dmarc-feedback@example.com;"
v=DMARC1; (version) v=DMARC1; (version)
p=none; (disposition policy : reject, quarantine, none (monitor)) p=none; (disposition policy : reject, quarantine, none (monitor))
@ -50,9 +50,7 @@ _dmarc IN TXT "v=DMARC1; p=reject; pct=100; rua=mailto:dmarc-feedback@example.c
2. install a public suffix list in config/public_suffix_list. See http://publicsuffix.org/list/ 2. install a public suffix list in config/public_suffix_list. See http://publicsuffix.org/list/
3. activate this plugin (add to config/plugins) 3. activate this plugin. (add to config/plugins, listing it after SPF & DKIM. Check that SPF and DKIM are configured to not reject mail.
Be sure to run the DMARC plugin after the SPF & DKIM plugins. Configure the SPF and DKIM messages to not reject mail.
=head2 Parse dmarc feedback reports into a database =head2 Parse dmarc feedback reports into a database
@ -68,23 +66,9 @@ https://github.com/qpsmtpd-dev/qpsmtpd-dev/wiki/DMARC-FAQ
2. provide dmarc feedback to domains that request it 2. provide dmarc feedback to domains that request it
3. If a message has multiple 'From' recipients, reject it =head1 AUTHORS
=head1 IMPLEMENTATION 2013 - Matt Simerson <msimerson@cpan.org>
1. Primary identifier is RFC5322.From field (From: header)
2. Senders can specify strict or relaxed mode
3. policies available: reject, quarantine, no action
4. DMARC overrides other public auth mechanisms
5. senders can specify a percentage of messages to which policy applies
6. Receivers should endeavour to reject or quarantine email if the
RFC5322.From purports to be from a domain that appears to be
either non-existent or incapable of receiving mail.
=cut =cut
@ -113,18 +97,17 @@ sub data_post_handler {
return DECLINED if $self->is_immune(); return DECLINED if $self->is_immune();
# 11.1. Extract Author Domain # 11.1. Extract Author Domain
my $from_dom = $self->get_from_dom($transaction) or return DECLINED;
my $from_host = $self->get_from_host($transaction) or return DECLINED; my $org_dom = $self->get_organizational_domain($from_dom);
my $org_host = $self->get_organizational_domain($from_host);
# 6. Receivers should reject email if the domain appears to not exist # 6. Receivers should reject email if the domain appears to not exist
if (!$self->exists_in_dns($from_host) && !$self->exists_in_dns($org_host)) { my $exists = $self->exists_in_dns($from_dom, $org_dom) or do {
$self->log(LOGINFO, "fail, $from_host not in DNS"); $self->log(LOGINFO, "fail, $from_dom not in DNS");
return $self->get_reject("RFC5322.From host appears non-existent"); return $self->get_reject("RFC5322.From host appears non-existent");
} };
# 11.2. Determine Handling Policy # 11.2. Determine Handling Policy
my $policy = $self->discover_policy($from_host) my $policy = $self->discover_policy($from_dom, $org_dom)
or return DECLINED; or return DECLINED;
# 3. Perform DKIM signature verification checks. A single email may # 3. Perform DKIM signature verification checks. A single email may
@ -139,11 +122,14 @@ sub data_post_handler {
# 5. Conduct identifier alignment checks. # 5. Conduct identifier alignment checks.
return DECLINED return DECLINED
if $self->is_aligned($from_host, $org_host, $policy, $spf_dom ); if $self->is_aligned($from_dom, $org_dom, $policy, $spf_dom );
# 6. Apply policy. Emails that fail the DMARC mechanism check are # 6. Apply policy. Emails that fail the DMARC mechanism check are
# disposed of in accordance with the discovered DMARC policy of the # disposed of in accordance with the discovered DMARC policy of the
# Domain Owner. See Section 6.2 for details. # Domain Owner. See Section 6.2 for details.
if ( $self->{_args}{is_subdomain} && defined $policy->{sp} ) {
return DECLINED if lc $policy->{sp} eq 'none';
};
return DECLINED if lc $policy->{p} eq 'none'; return DECLINED if lc $policy->{p} eq 'none';
my $pct = $policy->{pct} || 100; my $pct = $policy->{pct} || 100;
@ -156,7 +142,7 @@ sub data_post_handler {
} }
sub is_aligned { sub is_aligned {
my ($self, $from_host, $org_host, $policy, $spf_dom) = @_; my ($self, $from_dom, $org_dom, $policy, $spf_dom) = @_;
# 5. Conduct identifier alignment checks. With authentication checks # 5. Conduct identifier alignment checks. With authentication checks
# and policy discovery performed, the Mail Receiver checks if # and policy discovery performed, the Mail Receiver checks if
@ -169,14 +155,14 @@ sub is_aligned {
my $dkim_sigs = $self->connection->notes('dkim_pass_domains') || []; my $dkim_sigs = $self->connection->notes('dkim_pass_domains') || [];
foreach (@$dkim_sigs) { foreach (@$dkim_sigs) {
if ($_ eq $from_host) { # strict alignment if ($_ eq $from_dom) { # strict alignment, requires exact match
$self->log(LOGINFO, "pass, DKIM aligned"); $self->log(LOGINFO, "pass, DKIM aligned");
$self->adjust_karma(1); $self->adjust_karma(1);
return 1; return 1;
} }
next if $policy->{adkim} && lc $policy->{adkim} eq 's'; # strict pol. next if $policy->{adkim} && lc $policy->{adkim} eq 's'; # strict pol.
# default policy is relaxed # relaxed policy (default): Org. Dom must match a DKIM sig
if ( $_ eq $org_host ) { if ( $_ eq $org_dom ) {
$self->log(LOGINFO, "pass, DKIM aligned, relaxed"); $self->log(LOGINFO, "pass, DKIM aligned, relaxed");
$self->adjust_karma(1); $self->adjust_karma(1);
return 1; return 1;
@ -184,13 +170,13 @@ sub is_aligned {
} }
return 0 if ! $spf_dom; return 0 if ! $spf_dom;
if ($spf_dom eq $from_host) { if ($spf_dom eq $from_dom) {
$self->adjust_karma(1); $self->adjust_karma(1);
$self->log(LOGINFO, "pass, SPF aligned"); $self->log(LOGINFO, "pass, SPF aligned");
return 1; return 1;
} }
return 0 if ($policy->{aspf} && lc $policy->{aspf} eq 's' ); # strict pol return 0 if ($policy->{aspf} && lc $policy->{aspf} eq 's' ); # strict pol
if ($spf_dom eq $org_host) { if ($spf_dom eq $org_dom) {
$self->adjust_karma(1); $self->adjust_karma(1);
$self->log(LOGINFO, "pass, SPF aligned, relaxed"); $self->log(LOGINFO, "pass, SPF aligned, relaxed");
return 1; return 1;
@ -200,35 +186,16 @@ sub is_aligned {
}; };
sub discover_policy { sub discover_policy {
my ($self, $from_host) = @_; my ($self, $from_dom, $org_dom) = @_;
# 1. Mail Receivers MUST query the DNS for a DMARC TXT record... # 1. Mail Receivers MUST query the DNS for a DMARC TXT record...
my @matches = $self->fetch_dmarc_record($from_host); # 2. within my @matches = $self->fetch_dmarc_record($from_dom, $org_dom) or return;
if (0 == scalar @matches) {
# 3. If the set is now empty, the Mail Receiver MUST query the DNS for
# a DMARC TXT record at the DNS domain matching the Organizational
# Domain in place of the RFC5322.From domain in the message (if
# different). This record can contain policy to be asserted for
# subdomains of the Organizational Domain.
my $org_dom = $self->get_organizational_domain($from_host) or return;
if ($org_dom eq $from_host) {
$self->log(LOGINFO, "skip, no policy for $from_host (same org)");
return;
}
@matches = $self->fetch_dmarc_record($org_dom);
if (0 == scalar @matches) {
$self->log(LOGINFO, "skip, no policy for $from_host");
return;
}
}
# 4. Records that do not include a "v=" tag that identifies the # 4. Records that do not include a "v=" tag that identifies the
# current version of DMARC are discarded. # current version of DMARC are discarded.
@matches = grep /v=DMARC1/i, @matches; @matches = grep /v=DMARC1/i, @matches;
if (0 == scalar @matches) { if (0 == scalar @matches) {
$self->log(LOGINFO, "skip, no valid record for $from_host"); $self->log(LOGINFO, "skip, no valid record for $from_dom");
return; return;
} }
@ -280,7 +247,7 @@ sub has_valid_reporting_uri {
} }
sub get_organizational_domain { sub get_organizational_domain {
my ($self, $from_host) = @_; my ($self, $from_dom) = @_;
# 1. Acquire a "public suffix" list, i.e., a list of DNS domain # 1. Acquire a "public suffix" list, i.e., a list of DNS domain
# names reserved for registrations. http://publicsuffix.org/list/ # names reserved for registrations. http://publicsuffix.org/list/
@ -290,7 +257,7 @@ sub get_organizational_domain {
# labels. Number these labels from right-to-left; e.g. for # labels. Number these labels from right-to-left; e.g. for
# "example.com", "com" would be label 1 and "example" would be # "example.com", "com" would be label 1 and "example" would be
# label 2.; # label 2.;
my @labels = reverse split /\./, $from_host; my @labels = reverse split /\./, $from_dom;
# 3. Search the public suffix list for the name that matches the # 3. Search the public suffix list for the name that matches the
# largest number of labels found in the subject DNS domain. Let # largest number of labels found in the subject DNS domain. Let
@ -314,7 +281,7 @@ sub get_organizational_domain {
}; };
} }
return $from_host if $greatest == scalar @labels; # same return $from_dom if $greatest == scalar @labels; # same
# 4. Construct a new DNS domain name using the name that matched # 4. Construct a new DNS domain name using the name that matched
# from the public suffix list and prefixing to it the "x+1"th # from the public suffix list and prefixing to it the "x+1"th
@ -324,26 +291,29 @@ sub get_organizational_domain {
} }
sub exists_in_dns { sub exists_in_dns {
my ($self, $domain) = @_; my ($self, $domain, $org_dom) = @_;
# 6. Receivers should endeavour to reject or quarantine email if the # 6. Receivers should endeavour to reject or quarantine email if the
# RFC5322.From purports to be from a domain that appears to be # RFC5322.From purports to be from a domain that appears to be
# either non-existent or incapable of receiving mail. # either non-existent or incapable of receiving mail.
# I went back to the ADSP (from where DMARC this originated, which in turn # That's all the draft says. I went back to the DKIM ADSP (which led me to
# led me to the ietf-dkim email list where a handful of 'experts' failed to # the ietf-dkim email list where some 'experts' failed to agree on The Right
# agree on The Right Way to test domain validity. No direction was given. # Way to test domain validity. Let alone deliverability. They point out:
# They point out: # MX records aren't mandatory, and A|AAAA as fallback aren't reliable.
# MX records aren't mandatory. #
# A or AAAA records as fallback aren't reliable. # Some experimentation proved both cases in real world usage. Instead, I test
# existence by searching for a MX, NS, A, or AAAA record. Since this search
# I chose to query the From: domain name and match NS,MX,A,or AAAA records. # is repeated for the Organizational Name, if the NS query fails, there's no
# Since this search gets repeated for the Organizational Name, if it # delegation from the TLD. That's proven very reliable.
# fails for the O.N., there's no delegation from the TLD.
my $res = $self->init_resolver(8); my $res = $self->init_resolver(8);
return 1 if $self->host_has_rr('NS', $res, $domain); my @todo = $domain;
return 1 if $self->host_has_rr('MX', $res, $domain); push @todo, $org_dom if $domain ne $org_dom;
return 1 if $self->host_has_rr('A', $res, $domain); foreach ( @todo ) {
return 1 if $self->host_has_rr('AAAA', $res, $domain); return 1 if $self->host_has_rr('MX', $res, $_);
return 1 if $self->host_has_rr('NS', $res, $_);
return 1 if $self->host_has_rr('A', $res, $_);
return 1 if $self->host_has_rr('AAAA', $res, $_);
};
} }
sub host_has_rr { sub host_has_rr {
@ -370,12 +340,12 @@ sub host_has_rr {
}; };
sub fetch_dmarc_record { sub fetch_dmarc_record {
my ($self, $zone) = @_; my ($self, $zone, $org_dom) = @_;
# 1. Mail Receivers MUST query the DNS for a DMARC TXT record at the # 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 # DNS domain matching the one found in the RFC5322.From domain in
# the message. A possibly empty set of records is returned. # the message. A possibly empty set of records is returned.
$self->{_args}{is_subdomain} = defined $org_dom ? 0 : 1;
my $res = $self->init_resolver(); my $res = $self->init_resolver();
my $query = $res->send('_dmarc.' . $zone, 'TXT'); my $query = $res->send('_dmarc.' . $zone, 'TXT');
my @matches; my @matches;
@ -384,27 +354,43 @@ sub fetch_dmarc_record {
# 2. Records that do not start with a "v=" tag that identifies the # 2. Records that do not start with a "v=" tag that identifies the
# current version of DMARC are discarded. # current version of DMARC are discarded.
next if 'v=' ne substr($rr->txtdata, 0, 2); next if 'v=' ne lc substr($rr->txtdata, 0, 2);
next if 'v=spf' eq substr($rr->txtdata, 0, 5); # commonly found next if 'v=spf' eq lc substr($rr->txtdata, 0, 5); # SPF commonly found
$self->log(LOGINFO, $rr->txtdata); $self->log(LOGINFO, $rr->txtdata);
push @matches, join('', $rr->txtdata); push @matches, join('', $rr->txtdata);
} }
return @matches if scalar @matches; # found one! (at least)
# 3. If the set is now empty, the Mail Receiver MUST query the DNS for
# a DMARC TXT record at the DNS domain matching the Organizational
# Domain in place of the RFC5322.From domain in the message (if
# different). This record can contain policy to be asserted for
# subdomains of the Organizational Domain.
if ( defined $org_dom ) { # <- recursion break
if ( $org_dom eq $zone ) {
$self->log(LOGINFO, "skip, no policy for $zone (same org)");
return @matches;
};
return $self->fetch_dmarc_record($org_dom); # <- recursion
};
$self->log(LOGINFO, "skip, no policy for $zone");
return @matches; return @matches;
} }
sub get_from_host { sub get_from_dom {
my ($self, $transaction) = @_; my ($self, $transaction) = @_;
my $from = $transaction->header->get('From') or do { my $from = $transaction->header->get('From') or do {
$self->log(LOGINFO, "error, unable to retrieve From header!"); $self->log(LOGINFO, "error, unable to retrieve From header!");
return; return;
}; };
my ($from_host) = (split /@/, $from)[-1]; # grab everything after the @ my ($from_dom) = (split /@/, $from)[-1]; # grab everything after the @
($from_host) = split /\s+/, $from_host; # remove any trailing cruft ($from_dom) = split /\s+/, $from_dom; # remove any trailing cruft
chomp $from_host; chomp $from_dom; # remove \n
chop $from_host if '>' eq substr($from_host, -1, 1); chop $from_dom if '>' eq substr($from_dom, -1, 1); # remove closing >
$self->log(LOGDEBUG, "info, from_host is $from_host"); $self->log(LOGDEBUG, "info, from_dom is $from_dom");
return $from_host; return $from_dom;
} }
sub parse_policy { sub parse_policy {