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checkdmarc.py
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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""Validates and parses SPF amd DMARC DNS records"""
import logging
from collections import OrderedDict
from re import compile, IGNORECASE
import json
from csv import DictWriter
from argparse import ArgumentParser
import os
from time import sleep
from datetime import datetime, timedelta
import socket
import smtplib
import tempfile
import platform
import shutil
import atexit
import requests
from ssl import SSLError, CertificateError, create_default_context
from io import StringIO
from expiringdict import ExpiringDict
import publicsuffix2
import dns
import dns.resolver
import dns.exception
import timeout_decorator
from pyleri import (Grammar,
Regex,
Sequence,
List,
Repeat
)
import ipaddress
"""Copyright 2019 Sean Whalen
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License."""
__version__ = "4.4.4"
DMARC_VERSION_REGEX_STRING = r"v=DMARC1;"
BIMI_VERSION_REGEX_STRING = r"v=BIMI1;"
DMARC_TAG_VALUE_REGEX_STRING = r"([a-z]{1,5})=([\w.:@/+!,_\- ]+)"
BIMI_TAG_VALUE_REGEX_STRING = r"([a-z]{1})=(.*)"
MAILTO_REGEX_STRING = r"^(mailto):" \
r"([\w\-!#$%&'*+-/=?^_`{|}~]" \
r"[\w\-.!#$%&'*+-/=?^_`{|}~]*@[\w\-.]+)(!\w+)?"
SPF_VERSION_TAG_REGEX_STRING = "v=spf1"
SPF_MECHANISM_REGEX_STRING = r"([+\-~?])?(mx|ip4|ip6|exists|include|all|a|" \
r"redirect|exp|ptr)[:=]?([\w+/_.:\-{%}]*)"
AFTER_ALL_REGEX_STRING = "all .*"
DMARC_TAG_VALUE_REGEX = compile(DMARC_TAG_VALUE_REGEX_STRING)
BIMI_TAG_VALUE_REGEX = compile(BIMI_TAG_VALUE_REGEX_STRING)
MAILTO_REGEX = compile(MAILTO_REGEX_STRING)
SPF_MECHANISM_REGEX = compile(SPF_MECHANISM_REGEX_STRING, IGNORECASE)
AFTER_ALL_REGEX = compile(AFTER_ALL_REGEX_STRING, IGNORECASE)
USER_AGENT = "Mozilla/5.0 (({0} {1})) parsedmarc/{2}".format(
platform.system(),
platform.release(),
__version__
)
DNS_CACHE = ExpiringDict(max_len=200000, max_age_seconds=1800)
TLS_CACHE = ExpiringDict(max_len=200000, max_age_seconds=1800)
STARTTLS_CACHE = ExpiringDict(max_len=200000, max_age_seconds=1800)
TMPDIR = tempfile.mkdtemp()
def _cleanup():
"""Remove temporary files"""
shutil.rmtree(TMPDIR)
atexit.register(_cleanup)
class SMTPError(Exception):
"""Raised when SMTP error occurs"""
class SPFError(Exception):
"""Raised when a fatal SPF error occurs"""
def __init__(self, msg, data=None):
"""
Args:
msg (str): The error message
data (dict): A dictionary of data to include in the output
"""
self.data = data
Exception.__init__(self, msg)
class _SPFWarning(Exception):
"""Raised when a non-fatal SPF error occurs"""
class _SPFMissingRecords(_SPFWarning):
"""Raised when a mechanism in a ``SPF`` record is missing the requested
A/AAAA or MX records"""
class _SPFDuplicateInclude(_SPFWarning):
"""Raised when a duplicate SPF include is found"""
class _DMARCWarning(Exception):
"""Raised when a non-fatal DMARC error occurs"""
class _BIMIWarning(Exception):
"""Raised when a non-fatal BIMI error occurs"""
class _DMARCBestPracticeWarning(_DMARCWarning):
"""Raised when a DMARC record does not follow a best practice"""
class DNSException(Exception):
"""Raised when a general DNS error occurs"""
def __init__(self, error):
if isinstance(error, dns.exception.Timeout):
error.kwargs["timeout"] = round(error.kwargs["timeout"], 1)
class DMARCError(Exception):
"""Raised when a fatal DMARC error occurs"""
def __init__(self, msg, data=None):
"""
Args:
msg (str): The error message
data (dict): A dictionary of data to include in the results
"""
self.data = data
Exception.__init__(self, msg)
class SPFRecordNotFound(SPFError):
"""Raised when an SPF record could not be found"""
def __init__(self, error):
if isinstance(error, dns.exception.Timeout):
error.kwargs["timeout"] = round(error.kwargs["timeout"], 1)
class MultipleSPFRTXTRecords(SPFError):
"""Raised when multiple TXT spf1 records are found"""
class SPFSyntaxError(SPFError):
"""Raised when an SPF syntax error is found"""
class SPFTooManyDNSLookups(SPFError):
"""Raised when an SPF record requires too many DNS lookups (10 max)"""
def __init__(self, *args, **kwargs):
data = dict(dns_lookups=kwargs["dns_lookups"])
SPFError.__init__(self, args[0], data=data)
class SPFRedirectLoop(SPFError):
"""Raised when a SPF redirect loop is detected"""
class SPFIncludeLoop(SPFError):
"""Raised when a SPF include loop is detected"""
class DMARCRecordNotFound(DMARCError):
"""Raised when a DMARC record could not be found"""
def __init__(self, error):
if isinstance(error, dns.exception.Timeout):
error.kwargs["timeout"] = round(error.kwargs["timeout"], 1)
class DMARCSyntaxError(DMARCError):
"""Raised when a DMARC syntax error is found"""
class InvalidDMARCTag(DMARCSyntaxError):
"""Raised when an invalid DMARC tag is found"""
class InvalidDMARCTagValue(DMARCSyntaxError):
"""Raised when an invalid DMARC tag value is found"""
class InvalidDMARCReportURI(InvalidDMARCTagValue):
"""Raised when an invalid DMARC reporting URI is found"""
class UnrelatedTXTRecordFoundAtDMARC(DMARCError):
"""Raised when a TXT record unrelated to DMARC is found"""
class SPFRecordFoundWhereDMARCRecordShouldBe(UnrelatedTXTRecordFoundAtDMARC):
"""Raised when a SPF record is found where a DMARC record should be;
most likely, the ``_dmarc`` subdomain
record does not actually exist, and the request for ``TXT`` records was
redirected to the base domain"""
class DMARCRecordInWrongLocation(DMARCError):
"""Raised when a DMARC record is found at the root of a domain"""
class DMARCReportEmailAddressMissingMXRecords(_DMARCWarning):
"""Raised when a email address in a DMARC report URI is missing MX
records"""
class UnverifiedDMARCURIDestination(_DMARCWarning):
"""Raised when the destination of a DMARC report URI does not indicate
that it accepts reports for the domain"""
class MultipleDMARCRecords(DMARCError):
"""Raised when multiple DMARC records are found, in violation of
RFC 7486, section 6.6.3"""
class BIMIError(Exception):
"""Raised when a fatal BIMI error occurs"""
def __init__(self, msg, data=None):
"""
Args:
msg (str): The error message
data (dict): A dictionary of data to include in the results
"""
self.data = data
Exception.__init__(self, msg)
class BIMIRecordNotFound(BIMIError):
"""Raised when a BIMI record could not be found"""
def __init__(self, error):
if isinstance(error, dns.exception.Timeout):
error.kwargs["timeout"] = round(error.kwargs["timeout"], 1)
class BIMISyntaxError(BIMIError):
"""Raised when a BIMI syntax error is found"""
class InvalidBIMITag(BIMISyntaxError):
"""Raised when an invalid BIMI tag is found"""
class InvalidBIMITagValue(BIMISyntaxError):
"""Raised when an invalid BIMI tag value is found"""
class InvalidBIMIIndicatorURI(InvalidBIMITagValue):
"""Raised when an invalid BIMI indicator URI is found"""
class UnrelatedTXTRecordFoundAtBIMI(BIMIError):
"""Raised when a TXT record unrelated to BIMI is found"""
class SPFRecordFoundWhereBIMIRecordShouldBe(UnrelatedTXTRecordFoundAtBIMI):
"""Raised when a SPF record is found where a BIMI record should be;
most likely, the ``selector_bimi`` subdomain
record does not actually exist, and the request for ``TXT`` records was
redirected to the base domain"""
class BIMIRecordInWrongLocation(BIMIError):
"""Raised when a BIMI record is found at the root of a domain"""
class MultipleBIMIRecords(BIMIError):
"""Raised when multiple BIMI records are found"""
class _SPFGrammar(Grammar):
"""Defines Pyleri grammar for SPF records"""
version_tag = Regex(SPF_VERSION_TAG_REGEX_STRING)
mechanism = Regex(SPF_MECHANISM_REGEX_STRING, IGNORECASE)
START = Sequence(version_tag, Repeat(mechanism))
class _DMARCGrammar(Grammar):
"""Defines Pyleri grammar for DMARC records"""
version_tag = Regex(DMARC_VERSION_REGEX_STRING)
tag_value = Regex(DMARC_TAG_VALUE_REGEX_STRING)
START = Sequence(version_tag, List(tag_value, delimiter=";", opt=True))
class _BIMIGrammar(Grammar):
"""Defines Pyleri grammar for BIMI records"""
version_tag = Regex(BIMI_VERSION_REGEX_STRING)
tag_value = Regex(BIMI_TAG_VALUE_REGEX_STRING)
START = Sequence(version_tag, List(tag_value, delimiter=";", opt=True))
tag_values = OrderedDict(adkim=OrderedDict(name="DKIM Alignment Mode",
default="r",
description='In relaxed mode, '
'the Organizational '
'Domains of both the '
'DKIM-authenticated '
'signing domain (taken '
'from the value of the '
'"d=" tag in the '
'signature) and that '
'of the RFC 5322 '
'From domain '
'must be equal if the '
'identifiers are to be '
'considered aligned.'),
aspf=OrderedDict(name="SPF alignment mode",
default="r",
description='In relaxed mode, '
'the SPF-authenticated '
'domain and RFC5322 '
'From domain must have '
'the same '
'Organizational Domain. '
'In strict mode, only '
'an exact DNS domain '
'match is considered to '
'produce Identifier '
'Alignment.'),
fo=OrderedDict(name="Failure Reporting Options",
default="0",
description='Provides requested '
'options for generation '
'of failure reports. '
'Report generators MAY '
'choose to adhere to the '
'requested options. '
'This tag\'s content '
'MUST be ignored if '
'a "ruf" tag (below) is '
'not also specified. '
'The value of this tag is '
'a colon-separated list '
'of characters that '
'indicate failure '
'reporting options.',
values={
"0": 'Generate a DMARC failure '
'report if all underlying '
'authentication mechanisms '
'fail to produce an aligned '
'"pass" result.',
"1": 'Generate a DMARC failure '
'report if any underlying '
'authentication mechanism '
'produced something other '
'than an aligned '
'"pass" result.',
"d": 'Generate a DKIM failure '
'report if the message had '
'a signature that failed '
'evaluation, regardless of '
'its alignment. DKIM-'
'specific reporting is '
'described in AFRF-DKIM.',
"s": 'Generate an SPF failure '
'report if the message '
'failed SPF evaluation, '
'regardless of its alignment.'
' SPF-specific reporting is '
'described in AFRF-SPF'
}
),
p=OrderedDict(name="Requested Mail Receiver Policy",
description='Specifies the policy to '
'be enacted by the '
'Receiver at the '
'request of the '
'Domain Owner. The '
'policy applies to '
'the domain and to its '
'subdomains, unless '
'subdomain policy '
'is explicitly described '
'using the "sp" tag.',
values={
"none": 'The Domain Owner requests '
'no specific action be '
'taken regarding delivery '
'of messages.',
"quarantine": 'The Domain Owner '
'wishes to have '
'email that fails '
'the DMARC mechanism '
'check be treated by '
'Mail Receivers as '
'suspicious. '
'Depending on the '
'capabilities of the '
'MailReceiver, '
'this can mean '
'"place into spam '
'folder", '
'"scrutinize '
'with additional '
'intensity", and/or '
'"flag as '
'suspicious".',
"reject": 'The Domain Owner wishes '
'for Mail Receivers to '
'reject '
'email that fails the '
'DMARC mechanism check. '
'Rejection SHOULD '
'occur during the SMTP '
'transaction.'
}
),
pct=OrderedDict(name="Percentage",
default=100,
description='Integer percentage of '
'messages from the '
'Domain Owner\'s '
'mail stream to which '
'the DMARC policy is to '
'be applied. '
'However, this '
'MUST NOT be applied to '
'the DMARC-generated '
'reports, all of which '
'must be sent and '
'received unhindered. '
'The purpose of the '
'"pct" tag is to allow '
'Domain Owners to enact '
'a slow rollout of '
'enforcement of the '
'DMARC mechanism.'
),
rf=OrderedDict(name="Report Format",
default="afrf",
description='A list separated by '
'colons of one or more '
'report formats as '
'requested by the '
'Domain Owner to be '
'used when a message '
'fails both SPF and DKIM '
'tests to report details '
'of the individual '
'failure. Only "afrf" '
'(the auth-failure report '
'type) is currently '
'supported in the '
'DMARC standard.',
values={
"afrf": ' "Authentication Failure '
'Reporting Using the '
'Abuse Reporting Format", '
'RFC 6591, April 2012,'
'<http://www.rfc-'
'editor.org/info/rfc6591>'
}
),
ri=OrderedDict(name="Report Interval",
default=86400,
description='Indicates a request to '
'Receivers to generate '
'aggregate reports '
'separated by no more '
'than the requested '
'number of seconds. '
'DMARC implementations '
'MUST be able to provide '
'daily reports and '
'SHOULD be able to '
'provide hourly reports '
'when requested. '
'However, anything other '
'than a daily report is '
'understood to '
'be accommodated on a '
'best-effort basis.'
),
rua=OrderedDict(name="Aggregate Feedback Addresses",
description=' A comma-separated list '
'of DMARC URIs to which '
'aggregate feedback '
'is to be sent.'
),
ruf=OrderedDict(name="Forensic Feedback Addresses",
description=' A comma-separated list '
'of DMARC URIs to which '
'forensic feedback '
'is to be sent.'
),
sp=OrderedDict(name="Subdomain Policy",
description='Indicates the policy to '
'be enacted by the '
'Receiver at the request '
'of the Domain Owner. '
'It applies only to '
'subdomains of the '
'domain queried, and not '
'to the domain itself. '
'Its syntax is identical '
'to that of the "p" tag '
'defined above. If '
'absent, the policy '
'specified by the "p" '
'tag MUST be applied '
'for subdomains.'
),
v=OrderedDict(name="Version",
description='Identifies the record '
'retrieved as a DMARC '
'record. It MUST have the '
'value of "DMARC1". The '
'value of this tag MUST '
'match precisely; if it '
'does not or it is absent, '
'the entire retrieved '
'record MUST be ignored. '
'It MUST be the first '
'tag in the list.')
)
spf_qualifiers = {
"": "pass",
"?": "neutral",
"+": "pass",
"-": "fail",
"~": "softfail"
}
bimi_tags = OrderedDict(
v=OrderedDict(name="Version",
description='Identifies the record '
'retrieved as a BIMI '
'record. It MUST have the '
'value of "BIMI1". The '
'value of this tag MUST '
'match precisely; if it '
'does not or it is absent, '
'the entire retrieved '
'record MUST be ignored. '
'It MUST be the first '
'tag in the list.')
)
def get_base_domain(domain, use_fresh_psl=False):
"""
Gets the base domain name for the given domain
.. note::
Results are based on a list of public domain suffixes at
https://publicsuffix.org/list/public_suffix_list.dat.
Args:
domain (str): A domain or subdomain
use_fresh_psl (bool): Download a fresh Public Suffix List
Returns:
str: The base domain of the given domain
"""
psl_path = os.path.join(TMPDIR, "public_suffix_list.dat")
def download_psl():
url = "https://publicsuffix.org/list/public_suffix_list.dat"
# Use a browser-like user agent string to bypass some proxy blocks
headers = {"User-Agent": USER_AGENT}
fresh_psl = requests.get(url, headers=headers).text
with open(psl_path, "w", encoding="utf-8") as fresh_psl_file:
fresh_psl_file.write(fresh_psl)
domain = domain.lower()
if domain.endswith(".test") or domain.endswith(
".example") or domain.endswith(".invalid") or domain.endswith(
".localhost"):
parts = domain.strip(".").split(".")
if len(parts) == 1:
return parts[0]
else:
return ".".join(parts[-2::])
if use_fresh_psl:
if not os.path.exists(psl_path):
download_psl()
else:
psl_age = datetime.now() - datetime.fromtimestamp(
os.stat(psl_path).st_mtime)
if psl_age > timedelta(hours=24):
try:
download_psl()
except Exception as error:
logging.warning(
"Failed to download an updated PSL {0}".format(error))
with open(psl_path, encoding="utf-8") as psl_file:
psl = publicsuffix2.PublicSuffixList(psl_file)
return psl.get_public_suffix(domain)
else:
return publicsuffix2.get_sld(domain)
def _query_dns(domain, record_type, nameservers=None, timeout=2.0,
cache=None):
"""
Queries DNS
Args:
domain (str): The domain or subdomain to query about
record_type (str): The record type to query for
nameservers (list): A list of one or more nameservers to use
timeout (float): Sets the DNS timeout in seconds
cache (ExpiringDict): Cache storage
Returns:
list: A list of answers
"""
domain = str(domain).lower()
record_type = record_type.upper()
cache_key = "{0}_{1}".format(domain, record_type)
if cache is None:
cache = DNS_CACHE
if type(cache) is ExpiringDict:
records = cache.get(cache_key, None)
if records:
return records
resolver = dns.resolver.Resolver()
timeout = float(timeout)
if nameservers is not None:
resolver.nameservers = nameservers
resolver.timeout = timeout
resolver.lifetime = timeout
if record_type == "TXT":
resource_records = list(map(
lambda r: r.strings,
resolver.resolve(domain, record_type, lifetime=timeout)))
_resource_record = [
resource_record[0][:0].join(resource_record)
for resource_record in resource_records if resource_record]
records = [r.decode() for r in _resource_record]
else:
records = list(map(
lambda r: r.to_text().replace('"', '').rstrip("."),
resolver.resolve(domain, record_type, lifetime=timeout)))
if type(cache) is ExpiringDict:
cache[cache_key] = records
return records
def _get_nameservers(domain, nameservers=None, timeout=2.0):
"""
Queries DNS for a list of nameservers
Args:
domain (str): A domain name
nameservers (list): A list of nameservers to query
Returns:
list: A list of ``OrderedDicts``; each containing a ``preference``
integer and a ``hostname``
Raises:
:exc:`checkdmarc.DNSException`
"""
answers = []
try:
answers = _query_dns(domain, "NS", nameservers=nameservers,
timeout=timeout)
except dns.resolver.NXDOMAIN:
raise DNSException("The domain {0} does not exist".format(domain))
except dns.resolver.NoAnswer:
pass
except Exception as error:
raise DNSException(error)
return answers
def _get_mx_hosts(domain, nameservers=None, timeout=2.0):
"""
Queries DNS for a list of Mail Exchange hosts
Args:
domain (str): A domain name
nameservers (list): A list of nameservers to query
Returns:
list: A list of ``OrderedDicts``; each containing a ``preference``
integer and a ``hostname``
Raises:
:exc:`checkdmarc.DNSException`
"""
hosts = []
try:
logging.debug("Checking for MX records on {0}".format(domain))
answers = _query_dns(domain, "MX", nameservers=nameservers,
timeout=timeout)
for record in answers:
record = record.split(" ")
preference = int(record[0])
hostname = record[1].rstrip(".").strip().lower()
hosts.append(OrderedDict(
[("preference", preference), ("hostname", hostname)]))
hosts = sorted(hosts, key=lambda h: (h["preference"], h["hostname"]))
except dns.resolver.NXDOMAIN:
raise DNSException("The domain {0} does not exist".format(domain))
except dns.resolver.NoAnswer:
pass
except Exception as error:
raise DNSException(error)
return hosts
def _get_a_records(domain, nameservers=None, timeout=2.0):
"""
Queries DNS for A and AAAA records
Args:
domain (str): A domain name
nameservers (list): A list of nameservers to query
timeout (float): number of seconds to wait for an answer from DNS
Returns:
list: A sorted list of IPv4 and IPv6 addresses
Raises:
:exc:`checkdmarc.DNSException`
"""
qtypes = ["A", "AAAA"]
addresses = []
for qt in qtypes:
try:
addresses += _query_dns(domain, qt, nameservers=nameservers,
timeout=timeout)
except dns.resolver.NXDOMAIN:
raise DNSException("The domain {0} does not exist".format(domain))
except dns.resolver.NoAnswer:
# Sometimes a domain will only have A or AAAA records, but not both
pass
except Exception as error:
raise DNSException(error)
addresses = sorted(addresses)
return addresses
def _get_reverse_dns(ip_address, nameservers=None, timeout=2.0):
"""
Queries for an IP addresses reverse DNS hostname(s)
Args:
ip_address (str): An IPv4 or IPv6 address
Returns:
list: A list of reverse DNS hostnames
nameservers (list): A list of nameservers to query
timeout (float): number of seconds to wait for an answer from DNS
Raises:
:exc:`checkdmarc.DNSException`
"""
try:
name = dns.reversename.from_address(ip_address)
hostnames = _query_dns(name, "PTR", nameservers=nameservers,
timeout=timeout)
except dns.resolver.NXDOMAIN:
return []
except Exception as error:
raise DNSException(error)
return hostnames
def _get_txt_records(domain, nameservers=None, timeout=2.0):
"""
Queries DNS for TXT records
Args:
domain (str): A domain name
nameservers (list): A list of nameservers to query
timeout (float): number of seconds to wait for an answer from DNS
Returns:
list: A list of TXT records
Raises:
:exc:`checkdmarc.DNSException`
"""
try:
records = _query_dns(domain, "TXT", nameservers=nameservers,
timeout=timeout)
except dns.resolver.NXDOMAIN:
raise DNSException("The domain {0} does not exist".format(domain))
except dns.resolver.NoAnswer:
raise DNSException(
"The domain {0} does not have any TXT records".format(domain))
except Exception as error:
raise DNSException(error)
return records
def _query_dmarc_record(domain, nameservers=None, timeout=2.0):
"""
Queries DNS for a DMARC record
Args:
domain (str): A domain name
nameservers (list): A list of nameservers to query
timeout (float): number of seconds to wait for an record from DNS
Returns:
str: A record string or None
"""
target = "_dmarc.{0}".format(domain.lower())
dmarc_record = None
dmarc_record_count = 0
unrelated_records = []
try:
records = _query_dns(target, "TXT", nameservers=nameservers,
timeout=timeout)
for record in records:
if record.startswith("v=DMARC1"):
dmarc_record_count += 1
else:
unrelated_records.append(record)
if dmarc_record_count > 1:
raise MultipleDMARCRecords(
"Multiple DMARC policy records are not permitted - "
"https://tools.ietf.org/html/rfc7489#section-6.6.3")
if len(unrelated_records) > 0:
raise UnrelatedTXTRecordFoundAtDMARC(
"Unrelated TXT records were discovered. These should be "
"removed, as some receivers may not expect to find "
"unrelated TXT records "
"at {0}\n\n{1}".format(target, "\n\n".join(unrelated_records)))
dmarc_record = records[0]
except dns.resolver.NoAnswer:
try:
records = _query_dns(domain.lower(), "TXT",
nameservers=nameservers,
timeout=timeout)
for record in records:
if record.startswith("v=DMARC1"):
raise DMARCRecordInWrongLocation(
"The DMARC record must be located at "
"{0}, not {1}".format(target, domain.lower()))
except dns.resolver.NoAnswer:
pass
except dns.resolver.NXDOMAIN:
raise DMARCRecordNotFound(
"The domain {0} does not exist".format(domain))
except Exception as error:
DMARCRecordNotFound(error)
except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
pass
except Exception as error:
raise DMARCRecordNotFound(error)
return dmarc_record
def _query_bmi_record(domain, selector="default", nameservers=None,
timeout=2.0):
"""
Queries DNS for a BIMI record
Args:
domain (str): A domain name
selector: the BIMI selector
nameservers (list): A list of nameservers to query
timeout (float): number of seconds to wait for an record from DNS
Returns:
str: A record string or None
"""
target = "{0}._bimi.{1}".format(selector, domain.lower())
bimi_record = None
bmi_record_count = 0
unrelated_records = []
try:
records = _query_dns(target, "TXT", nameservers=nameservers,
timeout=timeout)
for record in records:
if record.startswith("v=BIMI1"):
bmi_record_count += 1
else:
unrelated_records.append(record)
if bmi_record_count > 1:
raise MultipleBIMIRecords(
"Multiple BMI records are not permitted")
if len(unrelated_records) > 0:
raise UnrelatedTXTRecordFoundAtDMARC(
"Unrelated TXT records were discovered. These should be "
"removed, as some receivers may not expect to find "
"unrelated TXT records "
"at {0}\n\n{1}".format(target, "\n\n".join(unrelated_records)))
bimi_record = records[0]
except dns.resolver.NoAnswer:
try:
records = _query_dns(domain.lower(), "TXT",
nameservers=nameservers,
timeout=timeout)
for record in records:
if record.startswith("v=BIMI1"):
raise BIMIRecordInWrongLocation(
"The BIMI record must be located at "
"{0}, not {1}".format(target, domain.lower()))
except dns.resolver.NoAnswer:
pass
except dns.resolver.NXDOMAIN:
raise BIMIRecordNotFound(
"The domain {0} does not exist".format(domain))
except Exception as error:
BIMIRecordNotFound(error)
except (dns.resolver.NXDOMAIN, dns.resolver.NoAnswer):
pass
except Exception as error:
raise BIMIRecordNotFound(error)
return bimi_record
def query_dmarc_record(domain, nameservers=None, timeout=2.0):
"""
Queries DNS for a DMARC record
Args:
domain (str): A domain name
nameservers (list): A list of nameservers to query
timeout (float): number of seconds to wait for an record from DNS
Returns:
OrderedDict: An ``OrderedDict`` with the following keys:
- ``record`` - the unparsed DMARC record string
- ``location`` - the domain where the record was found
- ``warnings`` - warning conditions found
Raises:
:exc:`checkdmarc.DMARCRecordNotFound`
:exc:`checkdmarc.DMARCRecordInWrongLocation`
:exc:`checkdmarc.MultipleDMARCRecords`
:exc:`checkdmarc.SPFRecordFoundWhereDMARCRecordShouldBe`
"""
logging.debug("Checking for a DMARC record on {0}".format(domain))
warnings = []
base_domain = get_base_domain(domain)
location = domain.lower()
record = _query_dmarc_record(domain, nameservers=nameservers,
timeout=timeout)
try:
root_records = _query_dns(domain.lower(), "TXT",
nameservers=nameservers,
timeout=timeout)
for root_record in root_records:
if root_record.startswith("v=DMARC1"):
warnings.append("DMARC record at root of {0} "
"has no effect".format(domain.lower()))
except Exception:
pass
if record is None and domain != base_domain:
record = _query_dmarc_record(base_domain, nameservers=nameservers,
timeout=timeout)
location = base_domain
if record is None:
raise DMARCRecordNotFound(