lemur/lemur/certificates/verify.py

131 lines
4.2 KiB
Python

"""
.. module: lemur.certificates.verify
:platform: Unix
:copyright: (c) 2018 by Netflix Inc., see AUTHORS for more
:license: Apache, see LICENSE for more details.
.. moduleauthor:: Kevin Glisson <kglisson@netflix.com>
"""
import requests
import subprocess
from requests.exceptions import ConnectionError, InvalidSchema
from cryptography import x509
from cryptography.hazmat.backends import default_backend
from lemur.utils import mktempfile
from lemur.common.utils import parse_certificate
def ocsp_verify(cert_path, issuer_chain_path):
"""
Attempts to verify a certificate via OCSP. OCSP is a more modern version
of CRL in that it will query the OCSP URI in order to determine if the
certificate has been revoked
:param cert_path:
:param issuer_chain_path:
:return bool: True if certificate is valid, False otherwise
"""
command = ['openssl', 'x509', '-noout', '-ocsp_uri', '-in', cert_path]
p1 = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
url, err = p1.communicate()
p2 = subprocess.Popen(['openssl', 'ocsp', '-issuer', issuer_chain_path,
'-cert', cert_path, "-url", url.strip()], stdout=subprocess.PIPE, stderr=subprocess.PIPE)
message, err = p2.communicate()
p_message = message.decode('utf-8')
if 'error' in p_message or 'Error' in p_message:
raise Exception("Got error when parsing OCSP url")
elif 'revoked' in p_message:
return
elif 'good' not in p_message:
raise Exception("Did not receive a valid response")
return True
def crl_verify(cert_path):
"""
Attempts to verify a certificate using CRL.
:param cert_path:
:return: True if certificate is valid, False otherwise
:raise Exception: If certificate does not have CRL
"""
with open(cert_path, 'rt') as c:
cert = parse_certificate(c.read())
distribution_points = cert.extensions.get_extension_for_oid(x509.OID_CRL_DISTRIBUTION_POINTS).value
for p in distribution_points:
point = p.full_name[0].value
try:
response = requests.get(point)
if response.status_code != 200:
raise Exception("Unable to retrieve CRL: {0}".format(point))
except InvalidSchema:
# Unhandled URI scheme (like ldap://); skip this distribution point.
continue
except ConnectionError:
raise Exception("Unable to retrieve CRL: {0}".format(point))
crl = x509.load_der_x509_crl(response.content, backend=default_backend())
for r in crl:
if cert.serial == r.serial_number:
try:
reason = r.extensions.get_extension_for_class(x509.CRLReason).value
# Handle "removeFromCRL" revoke reason as unrevoked; continue with the next distribution point.
# Per RFC 5280 section 6.3.3 (k): https://tools.ietf.org/html/rfc5280#section-6.3.3
if reason == x509.ReasonFlags.remove_from_crl:
break
except x509.ExtensionNotFound:
pass
return
return True
def verify(cert_path, issuer_chain_path):
"""
Verify a certificate using OCSP and CRL
:param cert_path:
:param issuer_chain_path:
:return: True if valid, False otherwise
"""
# OCSP is our main source of truth, in a lot of cases CRLs
# have been deprecated and are no longer updated
try:
return ocsp_verify(cert_path, issuer_chain_path)
except Exception as e:
try:
return crl_verify(cert_path)
except Exception as e:
raise Exception("Failed to verify")
def verify_string(cert_string, issuer_string):
"""
Verify a certificate given only it's string value
:param cert_string:
:param issuer_string:
:return: True if valid, False otherwise
"""
with mktempfile() as cert_tmp:
with open(cert_tmp, 'w') as f:
f.write(cert_string)
with mktempfile() as issuer_tmp:
with open(issuer_tmp, 'w') as f:
f.write(issuer_string)
status = verify(cert_tmp, issuer_tmp)
return status