Issue #12000: When a SSL certificate has a subjectAltName without any

dNSName entry, ssl.match_hostname() should use the subject's commonName.
Patch by Nicolas Bareil.

Lib/ssl.py

@@ -122,8 +122,9 @@ def match_hostname(cert, hostname):
             if _dnsname_to_pat(value).match(hostname):
                 return
             dnsnames.append(value)
-    if not san:
-        # The subject is only checked when subjectAltName is empty
+    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

Lib/test/test_ssl.py

@@ -277,6 +277,24 @@ class BasicSocketTests(unittest.TestCase):
                             (('organizationName', 'Google Inc'),))}
         fail(cert, 'mail.google.com')
 
+        # No DNS entry in subjectAltName but a commonName
+        cert = {'notAfter': 'Dec 18 23:59:59 2099 GMT',
+                'subject': ((('countryName', 'US'),),
+                            (('stateOrProvinceName', 'California'),),
+                            (('localityName', 'Mountain View'),),
+                            (('commonName', 'mail.google.com'),)),
+                'subjectAltName': (('othername', 'blabla'), )}
+        ok(cert, 'mail.google.com')
+
+        # No DNS entry subjectAltName and no commonName
+        cert = {'notAfter': 'Dec 18 23:59:59 2099 GMT',
+                'subject': ((('countryName', 'US'),),
+                            (('stateOrProvinceName', 'California'),),
+                            (('localityName', 'Mountain View'),),
+                            (('organizationName', 'Google Inc'),)),
+                'subjectAltName': (('othername', 'blabla'),)}
+        fail(cert, 'google.com')
+
         # Empty cert / no cert
         self.assertRaises(ValueError, ssl.match_hostname, None, 'example.com')
         self.assertRaises(ValueError, ssl.match_hostname, {}, 'example.com')

Misc/ACKS

@@ -50,6 +50,7 @@ Luigi Ballabio
 Jeff Balogh
 Matt Bandy
 Michael J. Barber
+Nicolas Bareil
 Chris Barker
 Nick Barnes
 Quentin Barnes

Misc/NEWS

@@ -140,6 +140,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #12000: When a SSL certificate has a subjectAltName without any
+  dNSName entry, ssl.match_hostname() should use the subject's commonName.
+  Patch by Nicolas Bareil.
+
 - Issue #10775: assertRaises, assertRaisesRegex, assertWarns, and
   assertWarnsRegex now accept a keyword argument 'msg' when used as context
   managers.  Initial patch by Winston Ewert.