140 lines
5.9 KiB
Python
140 lines
5.9 KiB
Python
import sys
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import logging
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import Milter
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from email.header import decode_header
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from email.utils import getaddresses
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import re
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import config
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# Basic logger that also logs to stdout
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# TODO: Improve this a lot.
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logger = logging.getLogger(__name__)
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logger.setLevel(config.log_level)
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handler = logging.StreamHandler(sys.stdout)
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handler.setLevel(config.log_level)
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formatter = logging.Formatter('%(asctime)s - %(levelname)s - %(message)s')
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handler.setFormatter(formatter)
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logger.addHandler(handler)
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# Rough regex to fetch domain values from address-like text
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# Not matching the part in front of @ because greedy and stuff :(
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address_domain_regex = re.compile('\@(?P<domain>[\.\w-]+)')
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def get_decoded_header(value):
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"""Use python builtins to decode encoding stuff from header properly."""
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decoded_header_items = decode_header(value)
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decoded_header_value = ''
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for item in decoded_header_items:
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try:
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decoded_item = item[0].decode(item[1], 'ignore') if item[1] is not None else item[0]
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except:
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logger.warning(f"Decoding went wrong for value '{value}'!")
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# Pretend decoded item is empty :-(
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decoded_item = ''
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if isinstance(decoded_item, bytes):
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decoded_item = decoded_item.decode('ascii', 'ignore')
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decoded_header_value += decoded_item
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return decoded_header_value
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def normalizeRawFromHeader(value):
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"""Clean up linebreaks and spaces that are not needed."""
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return value.replace('\n', '').replace('\r', '').strip()
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def getDomainFromValue(value):
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""" Check whether given 'From:' header label contains something that looks like an email address."""
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match = address_domain_regex.match(value)
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return match.group('domain').strip() if match is not None else None
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class SuspiciousFrom(Milter.Base):
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def __init__(self):
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self.id = Milter.uniqueID()
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self.reset()
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logger.debug(f"({self.id}) Instanciated.")
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def reset(self):
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"""It looks like one milter instance can reach eom hook multiple times.
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This allows to re-use an instance in a more clean way."""
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self.final_result = Milter.ACCEPT
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self.new_headers = []
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def set_suspicious_headers(self, is_suspicious, reason):
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str_okay = "PASS" if not is_suspicious else "FAIL"
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str_suspicious = "YES" if is_suspicious else "NO"
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self.new_headers.append({'name': 'X-From-Checked', 'value': f"{str_okay} - {reason}"})
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self.new_headers.append({'name': 'X-From-Suspicious', 'value': str_suspicious})
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def header(self, field, value):
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"""Header hook gets called for every header within the email processed."""
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if field.lower() == 'from':
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logger.debug(f"({self.id}) \"From:\" raw: '{value}'")
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value = normalizeRawFromHeader(value)
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logger.info(f"({self.id}) \"From:\" cleaned: '{value}'")
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if value == '':
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logger.warning(f"\"From:\" header empty! WTF, but nothing to do. OK for now.")
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self.set_suspicious_headers(False, "EMPTY FROM HEADER - WTF")
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else:
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decoded_from = get_decoded_header(value)
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logger.debug(f"({self.id}) \"From:\" decoded raw: '{value}'")
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decoded_from = normalizeRawFromHeader(decoded_from)
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logger.info(f"({self.id}) \"From:\" decoded cleaned: '{decoded_from}'")
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all_domains = address_domain_regex.findall(decoded_from)
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all_domains = [a.lower() for a in all_domains]
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if len(all_domains) == 0:
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logger.warning(f"({self.id}) No domain in decoded \"From:\" - WTF! OK, though")
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self.set_suspicious_headers(False, "No domains in decoded FROM")
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elif len(all_domains) == 1:
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logger.debug(f"({self.id}) Only one domain in decoded \"From:\": '{all_domains[0]}' - OK")
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self.set_suspicious_headers(False, "Only one domain in decoded FROM")
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else:
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logger.info(f"({self.id}) Raw decoded from header contains multiple domains: '{all_domains}' - Checking")
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if len(set(all_domains)) > 1:
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logger.info(f"({self.id}) Multiple different domains in decoded \"From:\". - NOT OK")
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self.set_suspicious_headers(True, "Multiple domains in decoded FROM are different")
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else:
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logger.info(f"({self.id}) All domains in decoded \"From:\" are identical - OK")
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self.set_suspicious_headers(False, "Multiple domains in decoded FROM match properly")
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# CONTINUE so we reach eom hook.
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# TODO: Log and react if multiple From-headers are found?
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return Milter.CONTINUE
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def eom(self):
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"""EOM hook gets called at the end of message processed. Headers and final verdict are applied only here."""
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logger.info(f"({self.id}) EOM: Final verdict is {self.final_result}. New headers: {self.new_headers}")
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for new_header in self.new_headers:
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self.addheader(new_header['name'], new_header['value'])
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logger.debug(f"({self.id}) EOM: Reseting self.")
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self.reset()
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return self.final_result
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def main():
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# TODO: Move this into configuration of some sort.
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Milter.factory = SuspiciousFrom
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logger.info(f"Starting Milter.")
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# This call blocks the main thread.
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# TODO: Improve handling CTRL+C
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Milter.runmilter("SuspiciousFromMilter", config.milter_socket, config.milter_timeout, rmsock=False)
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logger.info(f"Milter finished running.")
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def test():
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# simple method to deal with unexpected exceptions on the fly :(
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test_from_value = '=?UNKNOWN?Q?Nat=E1lia?= Reis via DBWorld <dbworld@cs.wisc.edu>'
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logger.info(f"Begin of test().")
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test_instance = SuspiciousFrom()
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test_instance.header('from', test_from_value)
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logger.info(f"End of test().")
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if __name__ == "__main__":
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#test()
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main()
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