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