File Coverage

lib/Mail/DMARC/PurePerl.pm

Criterion	Covered	Total	%
statement	267	296	90.2
branch	143	208	68.7
condition	33	59	55.9
subroutine	21	21	100.0
pod	13	17	76.4
total	477	601	79.3

package Mail::DMARC::PurePerl;
our $VERSION = '1.20210927';
use strict;
use warnings;

use Carp;

use parent 'Mail::DMARC';

sub init {
    my $self = shift;
    $self->is_subdomain(0);
    $self->{header_from} = undef;
    $self->{header_from_raw} = undef;
    $self->{envelope_to} = undef;
    $self->{envelope_from} = undef;
    $self->{source_ip} = undef;
    $self->{policy} = undef;
    $self->{result} = undef;
    $self->{report} = undef;
    $self->{spf} = undef;
    $self->{dkim} = undef;
    return;
}

sub validate {
    my $self   = shift;
    my $policy = shift;

    $self->result->result('fail');        # set a couple
    $self->result->disposition('none');   # defaults

    # 11.2.1 Extract RFC5322.From domain
    my $from_dom = $self->get_from_dom() or return $self->result;
    # 9.6. reject email if the domain appears to not exist
    $self->exists_in_dns() or return $self->result;
    $policy ||= $self->discover_policy();  # 11.2.2 Query DNS for DMARC policy
    $policy or return $self->result;

    #   3.5 Out of Scope  DMARC has no "short-circuit" provision, such as
    #         specifying that a pass from one authentication test allows one
    #         to skip the other(s). All are required for reporting.

    eval { $self->is_dkim_aligned; };  # 11.2.3. DKIM signature verification checks
    eval { $self->is_spf_aligned;  };  # 11.2.4. SPF validation checks
    my $aligned = $self->is_aligned(); # 11.2.5. identifier alignment checks

    if ($self->config->{report_store}{auto_save}) {
        eval { $self->save_aggregate(); };
    }

    return $self->result if $aligned;

    my $effective_p
        = $self->is_subdomain && defined $policy->sp
        ? $policy->sp
        : $policy->p;

    # 11.2.6 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.
    if ( lc $effective_p eq 'none' ) {
        return $self->result;
    }

    return $self->result if $self->is_whitelisted;

    # 7.1.  Policy Fallback Mechanism
    # If the "pct" tag is present in a policy record, application of policy
    # is done on a selective basis.
    if ( !defined $policy->pct ) {
        $self->result->disposition($effective_p);
        return $self->result;
    }

    # The stated percentage of messages that fail the DMARC test MUST be
    # subjected to whatever policy is selected by the "p" or "sp" tag
    if ( int( rand(100) ) < $policy->pct ) {
        $self->result->disposition($effective_p);
        return $self->result;
    }

    $self->result->reason( type => 'sampled_out' );

    # Those that are not thus selected MUST instead be subjected to the next
    # policy lower in terms of severity.  In decreasing order of severity,
    # the policies are "reject", "quarantine", and "none".
    $self->result->disposition(
        ( $effective_p eq 'reject' ) ? 'quarantine' : 'none' );
    return $self->result;
}

sub save_aggregate {
    my ( $self ) = @_;

    my $pol;
    eval { $pol = $self->result->published; };
    if ( $pol && $self->has_valid_reporting_uri($pol->rua) ) {
        my @valid_report_uris = $self->get_valid_reporting_uri($pol->rua);

        my $filtered_report_uris = join( ',',
            map { $_->{'uri'} . ( ( $_->{'max_bytes'} > 0 ) ? ( '!' . $_->{'max_bytes'} ) : q{} ) }
                @valid_report_uris
        );

        $self->result->published->rua( $filtered_report_uris );

        return $self->SUPER::save_aggregate();
    }
    return;
}

sub discover_policy {
    my $self     = shift;
    my $from_dom = shift || $self->header_from or croak;
    print "Header From: $from_dom\n" if $self->verbose;
    my $org_dom  = $self->get_organizational_domain($from_dom);

    # 9.1  Mail Receivers MUST query the DNS for a DMARC TXT record
    my ($matches, $at_dom) = $self->fetch_dmarc_record( $from_dom, $org_dom );
    if (0 == scalar @$matches ) {
        $self->result->result('none');
        $self->result->reason( type => 'other', comment => 'no policy' );
        return;
    };

    # 9.5. If the remaining set contains multiple records, processing
    #      terminates and the Mail Receiver takes no action.
    if ( scalar @$matches > 1 ) {
        $self->result->reason( type => 'other', comment => "too many policies" );
        print "Too many DMARC records\n" if $self->verbose;
        return;
    }

    my $policy;
    if (!$at_dom) { $at_dom = $from_dom; }
    my $policy_str = "domain=$at_dom;" . $matches->[0];  # prefix with domain
    eval { $policy = $self->policy( $policy_str ) } or return;
    if ($@) {
        $self->result->reason( type => 'other', comment => "policy parse error: $@" );
        return;
    };
    $self->result->published($policy);

    # 9.6 If a retrieved policy record does not contain a valid "p" tag, or
    #     contains an "sp" tag that is not valid, then:
    if (   !$policy->p
        || !$policy->is_valid_p( $policy->p )
        || ( defined $policy->sp && !$policy->is_valid_p( $policy->sp ) ) )
    {

        #   A.  if an "rua" tag is present and contains at least one
        #       syntactically valid reporting URI, the Mail Receiver SHOULD
        #       act as if a record containing a valid "v" tag and "p=none"
        #       was retrieved, and continue processing;
        #   B.  otherwise, the Mail Receiver SHOULD take no action.
        if (   !$policy->rua
            || !$self->has_valid_reporting_uri( $policy->rua ) )
        {
            $self->result->reason( type => 'other', comment => "no valid rua" );
            return;
        }
        $policy->v('DMARC1');
        $policy->p('none');
    }

    return $policy;
}

sub is_aligned {
    my $self = shift;

    # 11.2.5 Conduct identifier alignment checks.  With authentication checks
    #        and policy discovery performed, the Mail Receiver checks if
    #        Authenticated Identifiers fall into alignment as decribed in
    #        Section 4.  If one or more of the Authenticated Identifiers align
    #        with the RFC5322.From domain, the message is considered to pass
    #        the DMARC mechanism check.  All other conditions (authentication
    #        failures, identifier mismatches) are considered to be DMARC
    #        mechanism check failures.

    if (   'pass' eq $self->result->spf
        || 'pass' eq $self->result->dkim )
    {
        $self->result->result('pass');
        $self->result->disposition('none');
        return 1;
    }
    return 0;
}

sub is_dkim_aligned {
    my $self = shift;

    $self->result->dkim('fail');    # our 'default' result
    $self->get_dkim_pass_sigs() or return;

    # 11.2.3 Perform DKIM signature verification checks.  A single email may
    #        contain multiple DKIM signatures.  The results MUST include the
    #        value of the "d=" tag from all DKIM signatures that validated.

    my $from_dom = $self->header_from or croak "header_from not set!";
    my $policy   = $self->policy      or croak "no policy!?";
    my $from_org = $self->get_organizational_domain();

    # Required in report: DKIM-Domain, DKIM-Identity, DKIM-Selector
    foreach my $dkim_ref ( $self->get_dkim_pass_sigs() ) {
        my $dkim_dom = lc $dkim_ref->{domain};

        my $dkmeta = {
            domain   => $dkim_ref->{domain},
            selector => $dkim_ref->{selector},
            identity => '',                      # TODO, what is this?
        };

        if ( $dkim_dom eq $from_dom ) { # strict alignment requires exact match
            $self->result->dkim('pass');
            $self->result->dkim_align('strict');
            $self->result->dkim_meta($dkmeta);
            last;
        }

        # don't try relaxed if policy specifies strict
        next if $policy->adkim && 's' eq lc $policy->adkim;

        # don't try relaxed if we already got a strict match
        next if 'pass' eq $self->result->dkim;

        # relaxed policy (default): Org. Dom must match a DKIM sig
        my $dkim_org = $self->get_organizational_domain($dkim_dom);
        if ( $dkim_org eq $from_org ) {
            $self->result->dkim('pass');
            $self->result->dkim_align('relaxed');
            $self->result->dkim_meta($dkmeta);
        }
    }
    return 1 if 'pass' eq lc $self->result->dkim;
    return;
}

sub is_spf_aligned {
    my $self    = shift;
    my $spf_dom = shift;

    if ( !$spf_dom && !$self->spf ) { croak "missing SPF!"; }
    if ( !$spf_dom ) {
        my @passes = grep { $_->{result} && $_->{result} =~ /pass/i } @{ $self->spf };
        if (scalar @passes == 0) {
            $self->result->spf('fail');
            return 0;
        };
        my ($ref)  = grep { $_->{scope} && $_->{scope} eq 'mfrom' } @passes;
        if (!$ref) {
            ($ref) = grep { $_->{scope} && $_->{scope} eq 'helo' } @passes;
        }
        if (!$ref) { ($ref) = $passes[0]; };
        $spf_dom = $ref->{domain};
    };

    # 11.2.4 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.

    $self->result->spf('fail');
    return 0 if !$spf_dom;

    my $from_dom = $self->header_from or croak "header_from not set!";

    if ( $spf_dom eq $from_dom ) {
        $self->result->spf('pass');
        $self->result->spf_align('strict');
        return 1;
    }

    # don't try relaxed match if strict policy requested
    if ( $self->policy->aspf && 's' eq lc $self->policy->aspf ) {
        return 0;
    }

    if ( $self->get_organizational_domain($spf_dom) eq
         $self->get_organizational_domain($from_dom) )
    {
        $self->result->spf('pass');
        $self->result->spf_align('relaxed');
        return 1;
    }
    return 0;
}

sub is_whitelisted {
    my $self = shift;
    my $s_ip = shift || $self->source_ip;
    return if ! defined $s_ip;
    if ( ! $self->{_whitelist} ) {
        my $white_file = $self->config->{smtp}{whitelist} or return;
        return if ! -f $white_file || ! -r $white_file;
        foreach my $line ( split /\n/, $self->slurp($white_file) ) {
            next if $line =~ /^#/; # ignore comments
            my ($lip,$reason) = split /\s+/, $line, 2;
            $self->{_whitelist}{$lip} = $reason;
        };
    };
    return if ! $self->{_whitelist}{$s_ip};

    my ($type, $comment) = split /\s+/, $self->{_whitelist}{$s_ip}, 2;
    $self->result->disposition('none');
    $self->result->reason(
            type => $type,
            ($comment && $comment =~ /\S/ ? ('comment' => $comment) : () ),
            );
    return $type;
}

sub has_valid_reporting_uri {
    my ( $self, $rua ) = @_;
    my @valid_reporting_uris = $self->get_valid_reporting_uri( $rua );
    return scalar @valid_reporting_uris;
}

sub get_valid_reporting_uri {
    my ( $self, $rua ) = @_;
    return unless $rua;
    my $recips_ref = $self->report->uri->parse($rua);
    my @has_permission;
    foreach my $uri_ref (@$recips_ref) {
        if ( !$self->external_report( $uri_ref->{uri} ) ) {
            push @has_permission, $uri_ref;
            next;
        }
        my $ext = $self->verify_external_reporting($uri_ref);
        push @has_permission, $uri_ref if $ext;
    }
    return @has_permission;
}

sub get_dkim_pass_sigs {
    my $self = shift;

    my $dkim_sigs = $self->dkim or return ();    # message not signed

    if ( 'ARRAY' ne ref $dkim_sigs ) {
        croak "dkim needs to be an array reference!";
    }

    return grep { 'pass' eq lc $_->{result} } @$dkim_sigs;
}

sub get_organizational_domain {
    my $self = shift;
    my $from_dom = shift || $self->header_from
        or croak "missing header_from!";

    # 4.1 Acquire a "public suffix" list, i.e., a list of DNS domain
    #     names reserved for registrations. http://publicsuffix.org/list/

    # 4.2 Break the subject DNS domain name into a set of "n" ordered
    #     labels.  Number these labels from right-to-left; e.g. for
    #     "example.com", "com" would be label 1 and "example" would be
    #     label 2.;
    my @labels = reverse split /\./, lc $from_dom;

    # 4.3 Search the public suffix list for the name that matches the
    #     largest number of labels found in the subject DNS domain.  Let
    #     that number be "x".
    my $greatest = 0;
    for ( my $i = 0; $i <= scalar @labels; $i++ ) {
        next if !$labels[$i];
        my $tld = join '.', reverse( (@labels)[ 0 .. $i ] );

        if ( $self->is_public_suffix($tld) ) {
            $greatest = $i + 1;
        }
    }

    if ( $greatest == scalar @labels ) {    # same
        return $from_dom;
    }

    # 4.4 Construct a new DNS domain name using the name that matched
    #     from the public suffix list and prefixing to it the "x+1"th
    #     label from the subject domain. This new name is the
    #     Organizational Domain.
    my $org_dom = join '.', reverse( (@labels)[ 0 .. $greatest ] );
    print "Organizational Domain: $org_dom\n" if $self->verbose;
    return $org_dom;
}

sub exists_in_dns {
    my $self = shift;
    my $from_dom = shift || $self->header_from or croak "no header_from!";

  # rfc7489 6.6.3
  #     If the set produced by the mechanism above contains no DMARC policy
  #     record (i.e., any indication that there is no such record as opposed
  #     to a transient DNS error), Mail Receivers SHOULD NOT apply the DMARC
  #     mechanism to the message.

    my $org_dom = $self->get_organizational_domain($from_dom);
    my @todo    = $from_dom;
    if ( $from_dom ne $org_dom ) {
        push @todo, $org_dom;
        $self->is_subdomain(1);
    }
    my $matched = 0;
    foreach (@todo) {
        last if $matched;
        $matched++ and next if $self->has_dns_rr( 'MX',   $_ );
        $matched++ and next if $self->has_dns_rr( 'NS',   $_ );
        $matched++ and next if $self->has_dns_rr( 'A',    $_ );
        $matched++ and next if $self->has_dns_rr( 'AAAA', $_ );
    }
    if ( !$matched ) {
        $self->result->result('none');
        $self->result->disposition('none');
        $self->result->reason(
            type    => 'other',
            comment => "$from_dom not in DNS"
        );
    }
    return $matched;
}

sub fetch_dmarc_record {
    my ( $self, $zone, $org_dom ) = @_;

    # 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.
    $self->is_subdomain( defined $org_dom ? 0 : 1 );
    my @matches = ();
    my $query = $self->get_resolver->send( "_dmarc.$zone", 'TXT' )
        or return (\@matches, $zone);
    for my $rr ( $query->answer ) {
        next if $rr->type ne 'TXT';

        #   2.  Records that do not start with a "v=" tag that identifies the
        #       current version of DMARC are discarded.
        next if 'v=dmarc1' ne lc substr( $rr->txtdata, 0, 8 );
        print "\n" . $rr->txtdata . "\n\n" if $self->verbose;
        push @matches, join( '', $rr->txtdata );    # join long records
    }
    if (scalar @matches) {
        return \@matches, $zone;            # 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 ne $zone ) {
            return $self->fetch_dmarc_record($org_dom);    #  <- recursion
        }
    }

    return \@matches, $zone;
}

sub get_from_dom {
    my ($self) = @_;
    return $self->header_from if $self->header_from;

    my $header = $self->header_from_raw or do {
        $self->result->reason( type => 'other', comment => "no header_from" );
        return;
    };

    # TODO: the From header can contain multiple addresses and should be
    # parsed as described in RFC 2822. If From has multiple-addresses,
    # then parse and use the domain in the Sender header.

    # This returns only the domain in the last email address.
    # Caller can pass in pre-parsed from_dom if this doesn't suit them.
    #
    # I care only about the domain. This is way faster than RFC2822 parsing

    my ($from_dom) = ( split /@/, $header )[-1]; # grab everything after the @
    ($from_dom) = split /(\s+|>)/, lc $from_dom; # remove trailing cruft
    if ( !$from_dom ) {
        $self->result->reason(
            type    => 'other',
            comment => "invalid header_from: ($header)"
        );
        return;
    }
    return $self->header_from($from_dom);
}

sub external_report {
    my ( $self, $uri ) = @_;
    my $dmarc_dom = $self->result->published->domain
        or croak "published policy not tagged!";

    if ( 'mailto' eq $uri->scheme ) {
        my $dest_email = lc $uri->path;
        my ($dest_host) = ( split /@/, $dest_email )[-1];
        if ( $self->get_organizational_domain( $dest_host )
                eq
             $self->get_organizational_domain( $dmarc_dom )
             ) {
            print "$dest_host not external for $dmarc_dom\n" if $self->verbose;
            return 0;
        };
        print "$dest_host is external for $dmarc_dom\n" if $self->verbose;
    }

    if ( 'http' eq $uri->scheme ) {
        if ($uri->host eq $dmarc_dom ) {
            print $uri->host ." not external for $dmarc_dom\n" if $self->verbose;
            return 0;
        };
        print $uri->host ." is external for $dmarc_dom\n" if $self->verbose;
    }

    return 1;
}

sub verify_external_reporting {
    my $self = shift;
    my $uri_ref = shift or croak "missing URI";

    #  1.  Extract the host portion of the authority component of the URI.
    #      Call this the "destination host".
    my $dmarc_dom = $self->result->published->domain
        or croak "published policy not tagged!";

    my $dest_email = $uri_ref->{uri}->path or croak("invalid URI");
    my ($dest_host) = ( split /@/, $dest_email )[-1];

    #  2.  Prepend the string "_report._dmarc".
    #  3.  Prepend the domain name from which the policy was retrieved,
    #      after conversion to an A-label if needed.
    my $dest = join '.', $dmarc_dom, '_report._dmarc', $dest_host;

    #  4.  Query the DNS for a TXT record at the constructed name.
    my $query = $self->get_resolver->send( $dest, 'TXT' ) or do {
        print "\tquery for $dest failed\n" if $self->verbose;
        return;
    };

    #  5.  For each record, parse the result...same overall format:
    #      "v=DMARC1" tag is mandatory and MUST appear first in the list.
    my @matches;
    for my $rr ( $query->answer ) {
        next if $rr->type ne 'TXT';

        next if 'v=dmarc1' ne lc substr( $rr->txtdata, 0, 8 );
        my $policy = undef;
        my $dmarc_str = join( '', $rr->txtdata );    # join parts
        eval { $policy = $self->policy->parse($dmarc_str) }; ## no critic (Eval)
        push @matches, $policy ? $policy : $dmarc_str;
    }

    #  6.  If the result includes no TXT resource records...stop
    if ( !scalar @matches ) {
        print "\tno TXT match for $dest\n" if $self->verbose;
        return;
    };

    #  7.  If > 1 TXT resource record remains, external reporting authorized
    #  8.  If a "rua" or "ruf" tag is discovered, replace the
    #      corresponding value with the one found in this record.
    my @overrides = grep { ref $_ && $_->{rua} } @matches;
    foreach my $or (@overrides) {
        my $recips_ref = $self->report->uri->parse( $or->{rua} ) or next;
        if ( ( split /@/, $recips_ref->[0]{uri} )[-1] eq
            ( split /@/, $uri_ref->{uri} )[-1] )
        {
  # the overriding URI MUST use the same destination host from the first step.
            print "found override RUA: $or->{rua}\n" if $self->verbose;
            $self->result->published->rua( $or->{rua} );
        }
    }

    return @matches;
}

1;

__END__