bpo-32819: Simplify and improve ssl.match_hostname (#5620)
ssl.match_hostname() has been simplified and no longer depends on re and
ipaddress module for wildcard and IP addresses. Error reporting for invalid
wildcards has been improved.
Signed-off-by: Christian Heimes <christian@python.org>
diff --git a/Lib/ssl.py b/Lib/ssl.py
index f253769..ecdbb70 100644
--- a/Lib/ssl.py
+++ b/Lib/ssl.py
@@ -90,8 +90,6 @@
ALERT_DESCRIPTION_UNKNOWN_PSK_IDENTITY
"""
-import ipaddress
-import re
import sys
import os
from collections import namedtuple
@@ -160,6 +158,7 @@
from socket import socket, AF_INET, SOCK_STREAM, create_connection
from socket import SOL_SOCKET, SO_TYPE
+import socket as _socket
import base64 # for DER-to-PEM translation
import errno
import warnings
@@ -183,55 +182,75 @@
def _dnsname_match(dn, hostname):
"""Matching according to RFC 6125, section 6.4.3
- http://tools.ietf.org/html/rfc6125#section-6.4.3
+ - Hostnames are compared lower case.
+ - For IDNA, both dn and hostname must be encoded as IDN A-label (ACE).
+ - Partial wildcards like 'www*.example.org', multiple wildcards, sole
+ wildcard or wildcards in labels other then the left-most label are not
+ supported and a CertificateError is raised.
+ - A wildcard must match at least one character.
"""
- pats = []
if not dn:
return False
- leftmost, *remainder = dn.split(r'.')
-
- wildcards = leftmost.count('*')
- if wildcards == 1 and len(leftmost) > 1:
- # Only match wildcard in leftmost segment.
- raise CertificateError(
- "wildcard can only be present in the leftmost segment: " + repr(dn))
-
- if wildcards > 1:
- # 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))
-
+ wildcards = dn.count('*')
# 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'\*', '[^.]*'))
+ if wildcards > 1:
+ raise CertificateError(
+ "too many wildcards in certificate DNS name: {!r}.".format(dn))
- # add the remaining fragments, ignore any wildcards
- for frag in remainder:
- pats.append(re.escape(frag))
+ dn_leftmost, sep, dn_remainder = dn.partition('.')
- pat = re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)
- return pat.match(hostname)
+ if '*' in dn_remainder:
+ # Only match wildcard in leftmost segment.
+ raise CertificateError(
+ "wildcard can only be present in the leftmost label: "
+ "{!r}.".format(dn))
+
+ if not sep:
+ # no right side
+ raise CertificateError(
+ "sole wildcard without additional labels are not support: "
+ "{!r}.".format(dn))
+
+ if dn_leftmost != '*':
+ # no partial wildcard matching
+ raise CertificateError(
+ "partial wildcards in leftmost label are not supported: "
+ "{!r}.".format(dn))
+
+ hostname_leftmost, sep, hostname_remainder = hostname.partition('.')
+ if not hostname_leftmost or not sep:
+ # wildcard must match at least one char
+ return False
+ return dn_remainder.lower() == hostname_remainder.lower()
+
+
+def _inet_paton(ipname):
+ """Try to convert an IP address to packed binary form
+
+ Supports IPv4 addresses on all platforms and IPv6 on platforms with IPv6
+ support.
+ """
+ # inet_aton() also accepts strings like '1'
+ if ipname.count('.') == 3:
+ try:
+ return _socket.inet_aton(ipname)
+ except OSError:
+ pass
+
+ try:
+ return _socket.inet_pton(_socket.AF_INET6, ipname)
+ except OSError:
+ raise ValueError("{!r} is neither an IPv4 nor an IP6 "
+ "address.".format(ipname))
+ except AttributeError:
+ # AF_INET6 not available
+ pass
+
+ raise ValueError("{!r} is not an IPv4 address.".format(ipname))
def _ipaddress_match(ipname, host_ip):
@@ -241,14 +260,19 @@
(section 1.7.2 - "Out of Scope").
"""
# OpenSSL may add a trailing newline to a subjectAltName's IP address
- ip = ipaddress.ip_address(ipname.rstrip())
+ ip = _inet_paton(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*.
+ rules are followed.
+
+ The function matches IP addresses rather than dNSNames if hostname is a
+ valid ipaddress string. IPv4 addresses are supported on all platforms.
+ IPv6 addresses are supported on platforms with IPv6 support (AF_INET6
+ and inet_pton).
CertificateError is raised on failure. On success, the function
returns nothing.
@@ -258,7 +282,7 @@
"SSL socket or SSL context with either "
"CERT_OPTIONAL or CERT_REQUIRED")
try:
- host_ip = ipaddress.ip_address(hostname)
+ host_ip = _inet_paton(hostname)
except ValueError:
# Not an IP address (common case)
host_ip = None