Remove the fallback on commonName in match hostname function.

src/urllib3/__init__.py

@@ -69,8 +69,6 @@ def add_stderr_logger(level=logging.DEBUG):
 # mechanisms to silence them.
 # SecurityWarning's always go off by default.
 warnings.simplefilter("always", exceptions.SecurityWarning, append=True)
-# SubjectAltNameWarning's should go off once per host
-warnings.simplefilter("default", exceptions.SubjectAltNameWarning, append=True)
 # InsecurePlatformWarning's don't vary between requests, so we keep it default.
 warnings.simplefilter("default", exceptions.InsecurePlatformWarning, append=True)
 # SNIMissingWarnings should go off only once.

src/urllib3/connection.py

@@ -24,12 +24,7 @@ class BaseSSLError(BaseException):
 
 
 from ._version import __version__
-from .exceptions import (
-    ConnectTimeoutError,
-    NewConnectionError,
-    SubjectAltNameWarning,
-    SystemTimeWarning,
-)
+from .exceptions import ConnectTimeoutError, NewConnectionError, SystemTimeWarning
 from .packages.ssl_match_hostname import CertificateError, match_hostname
 from .util import SKIP_HEADER, SKIPPABLE_HEADERS, connection
 from .util.ssl_ import (
@@ -421,16 +416,6 @@ def connect(self):
             # the TLS library, this cannot always be done. So we check whether
             # the TLS Library still thinks it's matching hostnames.
             cert = self.sock.getpeercert()
-            if not cert.get("subjectAltName", ()):
-                warnings.warn(
-                    (
-                        f"Certificate for {hostname} has no `subjectAltName`, falling back to check for a "
-                        "`commonName` for now. This feature is being removed by major browsers and "
-                        "deprecated by RFC 2818. (See https://github.com/urllib3/urllib3/issues/497 "
-                        "for details.)"
-                    ),
-                    SubjectAltNameWarning,
-                )
             _match_hostname(cert, self.assert_hostname or server_hostname)
 
         self.is_verified = (

src/urllib3/exceptions.py

@@ -186,12 +186,6 @@ class SecurityWarning(HTTPWarning):
     pass
 
 
-class SubjectAltNameWarning(SecurityWarning):
-    """Warned when connecting to a host with a certificate missing a SAN."""
-
-    pass
-
-
 class InsecureRequestWarning(SecurityWarning):
     """Warned when making an unverified HTTPS request."""
 

src/urllib3/packages/ssl_match_hostname/_implementation.py

@@ -125,17 +125,6 @@ def match_hostname(cert, hostname):
             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 "
@@ -144,6 +133,4 @@ def match_hostname(cert, hostname):
     elif len(dnsnames) == 1:
         raise CertificateError(f"hostname {hostname!r} doesn't match {dnsnames[0]!r}")
     else:
-        raise CertificateError(
-            "no appropriate commonName or subjectAltName fields were found"
-        )
+        raise CertificateError("no appropriate subjectAltName fields were found")

test/conftest.py

@@ -75,20 +75,6 @@ def ip_san_server(tmp_path_factory):
         yield cfg
 
 
-@pytest.fixture
-def ipv6_addr_server(tmp_path_factory):
-    if not HAS_IPV6:
-        pytest.skip("Only runs on IPv6 systems")
-
-    tmpdir = tmp_path_factory.mktemp("certs")
-    ca = trustme.CA()
-    # IP address in Common Name
-    server_cert = ca.issue_cert(common_name="::1")
-
-    with run_server_in_thread("https", "::1", tmpdir, ca, server_cert) as cfg:
-        yield cfg
-
-
 @pytest.fixture
 def ipv6_san_server(tmp_path_factory):
     if not HAS_IPV6:

test/contrib/test_pyopenssl.py

@@ -34,9 +34,7 @@ def teardown_module():
 from ..with_dummyserver.test_https import (  # noqa: E402, F401
     TestHTTPS,
     TestHTTPS_IPSAN,
-    TestHTTPS_IPv6Addr,
     TestHTTPS_IPV6SAN,
-    TestHTTPS_NoSAN,
     TestHTTPS_TLSv1,
     TestHTTPS_TLSv1_1,
     TestHTTPS_TLSv1_2,

test/test_connection.py

@@ -4,6 +4,10 @@
 import pytest
 
 from urllib3.connection import RECENT_DATE, CertificateError, _match_hostname
+from urllib3.packages.ssl_match_hostname._implementation import (
+    CertificateError as ImplementationCertificateError,
+)
+from urllib3.packages.ssl_match_hostname._implementation import match_hostname
 
 
 class TestConnection:
@@ -43,6 +47,15 @@ def test_match_hostname_mismatch(self):
             )
             assert e._peer_cert == cert
 
+    def test_match_hostname_ignore_common_name(self):
+        cert = {"subject": [("commonName", "foo")]}
+        asserted_hostname = "foo"
+        with pytest.raises(
+            ImplementationCertificateError,
+            match="no appropriate subjectAltName fields were found",
+        ):
+            match_hostname(cert, asserted_hostname)
+
     def test_recent_date(self):
         # This test is to make sure that the RECENT_DATE value
         # doesn't get too far behind what the current date is.

test/with_dummyserver/test_https.py

@@ -782,22 +782,6 @@ class TestHTTPS_TLSv1_3(TestHTTPS):
     certs = TLSv1_3_CERTS
 
 
-class TestHTTPS_NoSAN:
-    def test_warning_for_certs_without_a_san(self, no_san_server):
-        """Ensure that a warning is raised when the cert from the server has
-        no Subject Alternative Name."""
-        with mock.patch("warnings.warn") as warn:
-            with HTTPSConnectionPool(
-                no_san_server.host,
-                no_san_server.port,
-                cert_reqs="CERT_REQUIRED",
-                ca_certs=no_san_server.ca_certs,
-            ) as https_pool:
-                r = https_pool.request("GET", "/")
-                assert r.status == 200
-                assert warn.called
-
-
 class TestHTTPS_IPSAN:
     def test_can_validate_ip_san(self, ip_san_server):
         """Ensure that urllib3 can validate SANs with IP addresses in them."""
@@ -816,19 +800,6 @@ def test_can_validate_ip_san(self, ip_san_server):
             assert r.status == 200
 
 
-class TestHTTPS_IPv6Addr:
-    def test_strip_square_brackets_before_validating(self, ipv6_addr_server):
-        """Test that the fix for #760 works."""
-        with HTTPSConnectionPool(
-            "[::1]",
-            ipv6_addr_server.port,
-            cert_reqs="CERT_REQUIRED",
-            ca_certs=ipv6_addr_server.ca_certs,
-        ) as https_pool:
-            r = https_pool.request("GET", "/")
-            assert r.status == 200
-
-
 class TestHTTPS_IPV6SAN:
     def test_can_validate_ipv6_san(self, ipv6_san_server):
         """Ensure that urllib3 can validate SANs with IPv6 addresses in them."""
@@ -845,3 +816,14 @@ def test_can_validate_ipv6_san(self, ipv6_san_server):
         ) as https_pool:
             r = https_pool.request("GET", "/")
             assert r.status == 200
+
+    def test_strip_square_brackets_before_validating(self, ipv6_san_server):
+        """Test that the fix for #760 works."""
+        with HTTPSConnectionPool(
+            "[::1]",
+            ipv6_san_server.port,
+            cert_reqs="CERT_REQUIRED",
+            ca_certs=ipv6_san_server.ca_certs,
+        ) as https_pool:
+            r = https_pool.request("GET", "/")
+            assert r.status == 200