Replace deprecated ssl.match_hostname method (fixes: #368)

The standard libraries's `ssl.match_hostname` method was marked as
deprecated in Python 3.10. Rather than implementing this critical piece
of code ourselves, make use of the Python Cryptographic Authority's
`service-identity` package.

One notable behaviour change is that validation is performed *only*
against the `subjectAltName` extension instead of the `commonName`. This
is the same behaviour as web browsers use.

pyproject.toml

@@ -29,6 +29,7 @@ dependencies = [
     "certifi",
     "pylsqpack>=0.3.3,<0.4.0",
     "pyopenssl>=22",
+    "service-identity>=23.1.0",
 ]
 dynamic = ["version"]
 

src/aioquic/tls.py

@@ -21,6 +21,7 @@
 )
 
 import certifi
+import service_identity
 from cryptography import x509
 from cryptography.exceptions import InvalidSignature
 from cryptography.hazmat.backends import default_backend
@@ -216,24 +217,14 @@ def verify_certificate(
 
     # verify subject
     if server_name is not None:
-        subject = []
-        subjectAltName: List[Tuple[str, str]] = []
-        for attr in certificate.subject:
-            if attr.oid == x509.NameOID.COMMON_NAME:
-                subject.append((("commonName", attr.value),))
-        for ext in certificate.extensions:
-            if isinstance(ext.value, x509.SubjectAlternativeName):
-                for name in ext.value:
-                    if isinstance(name, x509.DNSName):
-                        subjectAltName.append(("DNS", name.value))
-
         try:
-            ssl.match_hostname(
-                {"subject": tuple(subject), "subjectAltName": tuple(subjectAltName)},
-                server_name,
+            service_identity.cryptography.verify_certificate_hostname(
+                certificate, server_name
             )
-        except ssl.CertificateError as exc:
-            raise AlertBadCertificate("\n".join(exc.args)) from exc
+        except service_identity.VerificationError as exc:
+            raise AlertBadCertificate(
+                "Certificate does not match hostname '%s'" % server_name
+            ) from exc
 
     # load CAs
     store = crypto.X509Store()

tests/test_asyncio.py

@@ -149,19 +149,25 @@ async def _test_connect_and_serve_with_certificate(self, certificate, private_ke
     @asynctest
     async def test_connect_and_serve_with_ec_certificate(self):
         await self._test_connect_and_serve_with_certificate(
-            *generate_ec_certificate(common_name="localhost")
+            *generate_ec_certificate(
+                alternative_names=["localhost"], common_name="localhost"
+            )
         )
 
     @asynctest
     async def test_connect_and_serve_with_ed25519_certificate(self):
         await self._test_connect_and_serve_with_certificate(
-            *generate_ed25519_certificate(common_name="localhost")
+            *generate_ed25519_certificate(
+                alternative_names=["localhost"], common_name="localhost"
+            )
         )
 
     @asynctest
     async def test_connect_and_serve_with_ed448_certificate(self):
         await self._test_connect_and_serve_with_certificate(
-            *generate_ed448_certificate(common_name="localhost")
+            *generate_ed448_certificate(
+                alternative_names=["localhost"], common_name="localhost"
+            )
         )
 
     @asynctest

tests/test_tls.py

@@ -37,7 +37,6 @@
 )
 from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.primitives import serialization
-from cryptography.hazmat.primitives.asymmetric import ec
 
 from .utils import (
     SERVER_CACERTFILE,
@@ -1295,7 +1294,7 @@ def test_verify_certificate_chain(self):
 
     def test_verify_certificate_chain_self_signed(self):
         certificate, _ = generate_ec_certificate(
-            common_name="localhost", curve=ec.SECP256R1
+            alternative_names=["localhost"], common_name="localhost"
         )
 
         with patch("aioquic.tls.utcnow") as mock_utcnow:
@@ -1321,7 +1320,7 @@ def test_verify_certificate_chain_self_signed(self):
 
     def test_verify_dates(self):
         certificate, _ = generate_ec_certificate(
-            common_name="example.com", curve=ec.SECP256R1
+            alternative_names=["example.com"], common_name="example.com"
         )
         cadata = certificate.public_bytes(serialization.Encoding.PEM)
 
@@ -1360,45 +1359,26 @@ def test_verify_dates(self):
                 )
             self.assertEqual(str(cm.exception), "Certificate is no longer valid")
 
-    def test_verify_subject(self):
-        certificate, _ = generate_ec_certificate(
-            common_name="example.com", curve=ec.SECP256R1
-        )
+    def test_verify_subject_no_subjaltname(self):
+        certificate, _ = generate_ec_certificate(common_name="example.com")
         cadata = certificate.public_bytes(serialization.Encoding.PEM)
 
         with patch("aioquic.tls.utcnow") as mock_utcnow:
             mock_utcnow.return_value = certificate.not_valid_before
 
-            # valid
-            verify_certificate(
-                cadata=cadata, certificate=certificate, server_name="example.com"
-            )
-
-            # invalid
-            with self.assertRaises(tls.AlertBadCertificate) as cm:
-                verify_certificate(
-                    cadata=cadata,
-                    certificate=certificate,
-                    server_name="test.example.com",
-                )
-            self.assertEqual(
-                str(cm.exception),
-                "hostname 'test.example.com' doesn't match 'example.com'",
-            )
-
+            # certificates with no SubjectAltName are rejected
             with self.assertRaises(tls.AlertBadCertificate) as cm:
                 verify_certificate(
-                    cadata=cadata, certificate=certificate, server_name="acme.com"
+                    cadata=cadata, certificate=certificate, server_name="example.com"
                 )
             self.assertEqual(
-                str(cm.exception), "hostname 'acme.com' doesn't match 'example.com'"
+                str(cm.exception), "Certificate does not match hostname 'example.com'"
             )
 
     def test_verify_subject_with_subjaltname(self):
         certificate, _ = generate_ec_certificate(
             alternative_names=["*.example.com", "example.com"],
             common_name="example.com",
-            curve=ec.SECP256R1,
         )
         cadata = certificate.public_bytes(serialization.Encoding.PEM)
 
@@ -1419,7 +1399,5 @@ def test_verify_subject_with_subjaltname(self):
                     cadata=cadata, certificate=certificate, server_name="acme.com"
                 )
             self.assertEqual(
-                str(cm.exception),
-                "hostname 'acme.com' doesn't match either of '*.example.com', "
-                "'example.com'",
+                str(cm.exception), "Certificate does not match hostname 'acme.com'"
             )