/
ssl_match_hostname.py
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/
ssl_match_hostname.py
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"""The match_hostname() function from Python 3.3.3, essential when using SSL."""
# Note: This file is under the PSF license as the code comes from the python
# stdlib. http://docs.python.org/3/license.html
import re
import sys
# ipaddress has been backported to 2.6+ in pypi. If it is installed on the
# system, use it to handle IPAddress ServerAltnames (this was added in
# python-3.5) otherwise only do DNS matching. This allows
# util.ssl_match_hostname to continue to be used in Python 2.7.
try:
import ipaddress
except ImportError:
ipaddress = None
__version__ = "3.5.0.1"
class CertificateError(ValueError):
pass
def _dnsname_match(dn, hostname, max_wildcards=1):
"""Matching according to RFC 6125, section 6.4.3
http://tools.ietf.org/html/rfc6125#section-6.4.3
"""
pats = []
if not dn:
return False
# Ported from python3-syntax:
# leftmost, *remainder = dn.split(r'.')
parts = dn.split(r".")
leftmost = parts[0]
remainder = parts[1:]
wildcards = leftmost.count("*")
if wildcards > max_wildcards:
# Issue #17980: avoid denials of service by refusing more
# than one wildcard per fragment. A survey of established
# policy among SSL implementations showed it to be a
# reasonable choice.
raise CertificateError(
"too many wildcards in certificate DNS name: " + repr(dn)
)
# speed up common case w/o wildcards
if not wildcards:
return dn.lower() == hostname.lower()
# RFC 6125, section 6.4.3, subitem 1.
# The client SHOULD NOT attempt to match a presented identifier in which
# the wildcard character comprises a label other than the left-most label.
if leftmost == "*":
# When '*' is a fragment by itself, it matches a non-empty dotless
# fragment.
pats.append("[^.]+")
elif leftmost.startswith("xn--") or hostname.startswith("xn--"):
# RFC 6125, section 6.4.3, subitem 3.
# The client SHOULD NOT attempt to match a presented identifier
# where the wildcard character is embedded within an A-label or
# U-label of an internationalized domain name.
pats.append(re.escape(leftmost))
else:
# Otherwise, '*' matches any dotless string, e.g. www*
pats.append(re.escape(leftmost).replace(r"\*", "[^.]*"))
# add the remaining fragments, ignore any wildcards
for frag in remainder:
pats.append(re.escape(frag))
pat = re.compile(r"\A" + r"\.".join(pats) + r"\Z", re.IGNORECASE)
return pat.match(hostname)
def _to_unicode(obj):
if isinstance(obj, str) and sys.version_info < (3,):
# ignored flake8 # F821 to support python 2.7 function
obj = unicode(obj, encoding="ascii", errors="strict") # noqa: F821
return obj
def _ipaddress_match(ipname, host_ip):
"""Exact matching of IP addresses.
RFC 6125 explicitly doesn't define an algorithm for this
(section 1.7.2 - "Out of Scope").
"""
# OpenSSL may add a trailing newline to a subjectAltName's IP address
# Divergence from upstream: ipaddress can't handle byte str
ip = ipaddress.ip_address(_to_unicode(ipname).rstrip())
return ip == host_ip
def match_hostname(cert, hostname):
"""Verify that *cert* (in decoded format as returned by
SSLSocket.getpeercert()) matches the *hostname*. RFC 2818 and RFC 6125
rules are followed, but IP addresses are not accepted for *hostname*.
CertificateError is raised on failure. On success, the function
returns nothing.
"""
if not cert:
raise ValueError(
"empty or no certificate, match_hostname needs a "
"SSL socket or SSL context with either "
"CERT_OPTIONAL or CERT_REQUIRED"
)
try:
# Divergence from upstream: ipaddress can't handle byte str
host_ip = ipaddress.ip_address(_to_unicode(hostname))
except (UnicodeError, ValueError):
# ValueError: Not an IP address (common case)
# UnicodeError: Divergence from upstream: Have to deal with ipaddress not taking
# byte strings. addresses should be all ascii, so we consider it not
# an ipaddress in this case
host_ip = None
except AttributeError:
# Divergence from upstream: Make ipaddress library optional
if ipaddress is None:
host_ip = None
else: # Defensive
raise
dnsnames = []
san = cert.get("subjectAltName", ())
for key, value in san:
if key == "DNS":
if host_ip is None and _dnsname_match(value, hostname):
return
dnsnames.append(value)
elif key == "IP Address":
if host_ip is not None and _ipaddress_match(value, host_ip):
return
dnsnames.append(value)
if not dnsnames:
# The subject is only checked when there is no dNSName entry
# in subjectAltName
for sub in cert.get("subject", ()):
for key, value in sub:
# XXX according to RFC 2818, the most specific Common Name
# must be used.
if key == "commonName":
if _dnsname_match(value, hostname):
return
dnsnames.append(value)
if len(dnsnames) > 1:
raise CertificateError(
"hostname %r "
"doesn't match either of %s" % (hostname, ", ".join(map(repr, dnsnames)))
)
elif len(dnsnames) == 1:
raise CertificateError("hostname %r doesn't match %r" % (hostname, dnsnames[0]))
else:
raise CertificateError(
"no appropriate commonName or subjectAltName fields were found"
)