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validate certificates using the cryptography python package as much as possible, shelling out to openssl just once instead of four times per certificate

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* Use `cryptography` instead of parsing openssl's output.
* When checking if we can reuse the primary domain certificate or a www-parent-domain certificate for a domain, avoid shelling out to openssl entirely.
This commit is contained in:
Joshua Tauberer 2015-06-21 10:36:41 -04:00
parent 6a9eb4e367
commit dece359c90
4 changed files with 105 additions and 80 deletions
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1
CHANGELOG.md
View File

@ -20,6 +20,7 @@ DNS:
Control panel:
* Resetting a user's password now forces them to log in again everywhere.
* Status checks were not working if an ssh server was not installed.
* SSL certificate validation now uses the Python cryptography module in some places where openssl was used.
System:
* The munin system monitoring tool is now installed and accessible at /admin/munin.

174
management/status_checks.py
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@ -605,103 +605,101 @@ def check_ssl_cert(domain, rounded_time, env, output):
output.print_line(cert_status_details)
output.print_line("")
def check_certificate(domain, ssl_certificate, ssl_private_key, warn_if_expiring_soon=True, rounded_time=False):
# Use openssl verify to check the status of a certificate.
def check_certificate(domain, ssl_certificate, ssl_private_key, warn_if_expiring_soon=True, rounded_time=False, just_check_domain=False):
# Check that the ssl_certificate & ssl_private_key files are good
# for the provided domain.
# First check that the certificate is for the right domain. The domain
# must be found in the Subject Common Name (CN) or be one of the
# Subject Alternative Names. A wildcard might also appear as the CN
# or in the SAN list, so check for that tool.
retcode, cert_dump = shell('check_output', [
"openssl", "x509",
"-in", ssl_certificate,
"-noout", "-text", "-nameopt", "rfc2253",
], trap=True)
from cryptography.hazmat.primitives.asymmetric.rsa import RSAPrivateKey
from cryptography.x509 import Certificate, DNSName, ExtensionNotFound, OID_COMMON_NAME, OID_SUBJECT_ALTERNATIVE_NAME
# If the certificate is catastrophically bad, catch that now and report it.
# More information was probably written to stderr (which we aren't capturing),
# but it is probably not helpful to the user anyway.
if retcode != 0:
return ("The SSL certificate appears to be corrupted or not a PEM-formatted SSL certificate file. (%s)" % ssl_certificate, None)
# The ssl_certificate file may contain a chain of certificates. We'll
# need to split that up before we can pass anything to openssl or
# parse them in Python. Parse it with the cryptography library.
try:
ssl_cert_chain = load_cert_chain(ssl_certificate)
cert = load_pem(ssl_cert_chain[0])
if not isinstance(cert, Certificate): raise ValueError("This is not a certificate file.")
except ValueError as e:
return ("There is a problem with the certificate file: %s" % str(e), None)
cert_dump = cert_dump.split("\n")
certificate_names = set()
cert_expiration_date = None
while len(cert_dump) > 0:
line = cert_dump.pop(0)
# First check that the domain name is one of the names allowed by
# the certificate.
if domain is not None:
# The domain must be found in the Subject Common Name (CN)...
certificate_names = set()
try:
certificate_names.add(
cert.subject.get_attributes_for_oid(OID_COMMON_NAME)[0].value
)
except IndexError:
# No common name? Certificate is probably generated incorrectly.
# But we'll let it error-out when it doesn't find the domain.
pass
# Grab from the Subject Common Name. We include the indentation
# at the start of the line in case maybe the cert includes the
# common name of some other referenced entity (which would be
# indented, I hope).
m = re.match(" Subject: CN=([^,]+)", line)
if m:
certificate_names.add(m.group(1))
# Grab from the Subject Alternative Name, which is a comma-delim
# list of names, like DNS:mydomain.com, DNS:otherdomain.com.
m = re.match(" X509v3 Subject Alternative Name:", line)
if m:
names = re.split(",\s*", cert_dump.pop(0).strip())
for n in names:
m = re.match("DNS:(.*)", n)
if m:
certificate_names.add(m.group(1))
# ... or be one of the Subject Alternative Names.
try:
sans = cert.extensions.get_extension_for_oid(OID_SUBJECT_ALTERNATIVE_NAME).value.get_values_for_type(DNSName)
for san in sans:
certificate_names.add(san)
except ExtensionNotFound:
pass
# Grab the expiration date for testing later.
m = re.match(" Not After : (.*)", line)
if m:
cert_expiration_date = dateutil.parser.parse(m.group(1))
# Check that the domain appears among the acceptable names, or a wildcard
# form of the domain name (which is a stricter check than the specs but
# should work in normal cases).
wildcard_domain = re.sub("^[^\.]+", "*", domain)
if domain not in certificate_names and wildcard_domain not in certificate_names:
return ("The certificate is for the wrong domain name. It is for %s."
% ", ".join(sorted(certificate_names)), None)
wildcard_domain = re.sub("^[^\.]+", "*", domain)
if domain is not None and domain not in certificate_names and wildcard_domain not in certificate_names:
return ("The certificate is for the wrong domain name. It is for %s."
% ", ".join(sorted(certificate_names)), None)
# Second, check that the certificate matches the private key. Get the modulus of the
# private key and of the public key in the certificate. They should match. The output
# of each command looks like "Modulus=XXXXX".
# Second, check that the certificate matches the private key.
if ssl_private_key is not None:
private_key_modulus = shell('check_output', [
"openssl", "rsa",
"-inform", "PEM",
"-noout", "-modulus",
"-in", ssl_private_key])
cert_key_modulus = shell('check_output', [
"openssl", "x509",
"-in", ssl_certificate,
"-noout", "-modulus"])
if private_key_modulus != cert_key_modulus:
return ("The certificate installed at %s does not correspond to the private key at %s." % (ssl_certificate, ssl_private_key), None)
priv_key = load_pem(open(ssl_private_key, 'rb').read())
if not isinstance(priv_key, RSAPrivateKey):
return ("The private key file %s is not a private key file." % ssl_private_key, None)
if priv_key.public_key().public_numbers() != cert.public_key().public_numbers():
return ("The certificate does not correspond to the private key at %s." % ssl_private_key, None)
# We could also use the openssl command line tool to get the modulus
# listed in each file. The output of each command below looks like "Modulus=XXXXX".
# $ openssl rsa -inform PEM -noout -modulus -in ssl_private_key
# $ openssl x509 -in ssl_certificate -noout -modulus
# Third, check if the certificate is self-signed. Return a special flag string.
if cert.issuer == cert.subject:
return ("SELF-SIGNED", None)
# When selecting which certificate to use for non-primary domains, we check if the primary
# certificate or a www-parent-domain certificate is good for the domain. There's no need
# to run extra checks beyond this point.
if just_check_domain:
return ("OK", None)
# Check that the certificate hasn't expired. The datetimes returned by the
# certificate are 'naive' and in UTC. We need to get the current time in UTC.
now = datetime.datetime.utcnow()
if not(cert.not_valid_before <= now <= cert.not_valid_after):
return ("The certificate has expired or is not yet valid. It is valid from %s to %s." % (cert.not_valid_before, cert.not_valid_after), None)
# Next validate that the certificate is valid. This checks whether the certificate
# is self-signed, that the chain of trust makes sense, that it is signed by a CA
# that Ubuntu has installed on this machine's list of CAs, and I think that it hasn't
# expired.
# In order to verify with openssl, we need to split out any
# intermediary certificates in the chain (if any) from our
# certificate (at the top). They need to be passed separately.
cert = open(ssl_certificate).read()
m = re.match(r'(-*BEGIN CERTIFICATE-*.*?-*END CERTIFICATE-*)(.*)', cert, re.S)
if m == None:
return ("The certificate file is an invalid PEM certificate.", None)
mycert, chaincerts = m.groups()
# The certificate chain has to be passed separately and is given via STDIN.
# This command returns a non-zero exit status in most cases, so trap errors.
retcode, verifyoutput = shell('check_output', [
"openssl",
"verify", "-verbose",
"-purpose", "sslserver", "-policy_check",]
+ ([] if chaincerts.strip() == "" else ["-untrusted", "/dev/stdin"])
+ ([] if len(ssl_cert_chain) == 1 else ["-untrusted", "/dev/stdin"])
+ [ssl_certificate],
input=chaincerts.encode('ascii'),
input=b"\n\n".join(ssl_cert_chain[1:]),
trap=True)
if "self signed" in verifyoutput:
# Certificate is self-signed.
# Certificate is self-signed. Probably we detected this above.
return ("SELF-SIGNED", None)
elif retcode != 0:
@ -716,7 +714,7 @@ def check_certificate(domain, ssl_certificate, ssl_private_key, warn_if_expiring
# good.
# But is it expiring soon?
now = datetime.datetime.now(dateutil.tz.tzlocal())
cert_expiration_date = cert.not_valid_after
ndays = (cert_expiration_date-now).days
if not rounded_time or ndays < 7:
expiry_info = "The certificate expires in %d days on %s." % (ndays, cert_expiration_date.strftime("%x"))
@ -733,6 +731,30 @@ def check_certificate(domain, ssl_certificate, ssl_private_key, warn_if_expiring
# Return the special OK code.
return ("OK", expiry_info)
def load_cert_chain(pemfile):
# A certificate .pem file may contain a chain of certificates.
# Load the file and split them apart.
re_pem = rb"(-+BEGIN (?:.+)-+[\r\n](?:[A-Za-z0-9+/=]{1,64}[\r\n])+-+END (?:.+)-+[\r\n])"
with open(pemfile, "rb") as f:
pem = f.read() + b"\n" # ensure trailing newline
pemblocks = re.findall(re_pem, pem)
if len(pemblocks) == 0:
raise ValueError("File does not contain valid PEM data.")
return pemblocks
def load_pem(pem):
# Parse a "---BEGIN .... END---" PEM string and return a Python object for it
# using classes from the cryptography package.
from cryptography.x509 import load_pem_x509_certificate
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.backends import default_backend
pem_type = re.match(b"-+BEGIN (.*?)-+\n", pem).group(1)
if pem_type == b"RSA PRIVATE KEY":
return serialization.load_pem_private_key(pem, password=None, backend=default_backend())
if pem_type == b"CERTIFICATE":
return load_pem_x509_certificate(pem, default_backend())
raise ValueError("Unsupported PEM object type: " + pem_type.decode("ascii", "replace"))
_apt_updates = None
def list_apt_updates(apt_update=True):
# See if we have this information cached recently.

4
management/web_update.py
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@ -201,14 +201,14 @@ def get_domain_ssl_files(domain, env, allow_shared_cert=True):
# the user has uploaded a different private key for this domain.
if not ssl_key_is_alt and allow_shared_cert:
from status_checks import check_certificate
if check_certificate(domain, ssl_certificate_primary, None)[0] == "OK":
if check_certificate(domain, ssl_certificate_primary, None, just_check_domain=True)[0] == "OK":
ssl_certificate = ssl_certificate_primary
ssl_via = "Using multi/wildcard certificate of %s." % env['PRIMARY_HOSTNAME']
# For a 'www.' domain, see if we can reuse the cert of the parent.
elif domain.startswith('www.'):
ssl_certificate_parent = os.path.join(env["STORAGE_ROOT"], 'ssl/%s/ssl_certificate.pem' % safe_domain_name(domain[4:]))
if os.path.exists(ssl_certificate_parent) and check_certificate(domain, ssl_certificate_parent, None)[0] == "OK":
if os.path.exists(ssl_certificate_parent) and check_certificate(domain, ssl_certificate_parent, None, just_check_domain=True)[0] == "OK":
ssl_certificate = ssl_certificate_parent
ssl_via = "Using multi/wildcard certificate of %s." % domain[4:]

6
setup/management.sh
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@ -2,8 +2,10 @@
source setup/functions.sh
apt_install python3-flask links duplicity libyaml-dev python3-dnspython python3-dateutil
hide_output pip3 install rtyaml "email_validator==0.1.0-rc5"
# build-essential libssl-dev libffi-dev python3-dev: Required to pip install cryptography.
apt_install python3-flask links duplicity libyaml-dev python3-dnspython python3-dateutil \
build-essential libssl-dev libffi-dev python3-dev
hide_output pip3 install rtyaml "email_validator==0.1.0-rc5" cryptography
# email_validator is repeated in setup/questions.sh
# Create a backup directory and a random key for encrypting backups.