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# Backport of the match_hostname logic from python 3.5, with small
# changes to support IP address matching on python 2.6, 2.7, 3.3, and 3.4.
import re
import sys
# Python 3.3+, or the ipaddress module from pypi.
from ipaddress import ip_address
except ImportError:
ip_address = lambda address: None
# ipaddress.ip_address requires unicode
if sys.version_info[0] < 3:
_unicode = unicode
_unicode = lambda value: value
class CertificateError(ValueError):
def _dnsname_match(dn, hostname, max_wildcards=1):
"""Matching according to RFC 6125, section 6.4.3
pats = []
if not dn:
return False
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.
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.
# 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:
pat = re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)
return pat.match(hostname)
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
ip = ip_address(_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.
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 "
host_ip = ip_address(_unicode(hostname))
except (ValueError, UnicodeError):
# Not an IP address (common case)
host_ip = None
dnsnames = []
san = cert.get('subjectAltName', ())
for key, value in san:
if key == 'DNS':
if host_ip is None and _dnsname_match(value, hostname):
elif key == 'IP Address':
if host_ip is not None and _ipaddress_match(value, host_ip):
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):
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]))
raise CertificateError("no appropriate commonName or "
"subjectAltName fields were found")