Issue #20207: Always disable SSLv2 except when PROTOCOL_SSLv2 is explicitly asked for.

Lib/test/test_ssl.py

@@ -534,9 +534,7 @@ class ContextTests(unittest.TestCase):
     @skip_if_broken_ubuntu_ssl
     def test_options(self):
         ctx = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
-        # OP_ALL is the default value
-        self.assertEqual(ssl.OP_ALL, ctx.options)
-        ctx.options |= ssl.OP_NO_SSLv2
+        # OP_ALL | OP_NO_SSLv2 is the default value
         self.assertEqual(ssl.OP_ALL | ssl.OP_NO_SSLv2,
                          ctx.options)
         ctx.options |= ssl.OP_NO_SSLv3
@@ -1585,7 +1583,7 @@ else:
             try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv2, True)
             try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv2, True, ssl.CERT_OPTIONAL)
             try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv2, True, ssl.CERT_REQUIRED)
-            try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv23, True)
+            try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv23, False)
             try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv3, False)
             try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_TLSv1, False)
             # SSLv23 client with specific SSL options
@@ -1593,9 +1591,9 @@ else:
                 # No SSLv2 => client will use an SSLv3 hello on recent OpenSSLs
                 try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv23, False,
                                    client_options=ssl.OP_NO_SSLv2)
-            try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv23, True,
+            try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv23, False,
                                client_options=ssl.OP_NO_SSLv3)
-            try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv23, True,
+            try_protocol_combo(ssl.PROTOCOL_SSLv2, ssl.PROTOCOL_SSLv23, False,
                                client_options=ssl.OP_NO_TLSv1)
 
         @skip_if_broken_ubuntu_ssl

Misc/NEWS

@@ -43,6 +43,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #20207: Always disable SSLv2 except when PROTOCOL_SSLv2 is explicitly
+  asked for.
+
 - Issue #18960: The tokenize module now ignore the source encoding declaration
   on the second line if the first line contains anything except a comment.
 

Modules/_ssl.c

@@ -1737,6 +1737,7 @@ context_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     char *kwlist[] = {"protocol", NULL};
     PySSLContext *self;
     int proto_version = PY_SSL_VERSION_SSL23;
+    long options;
     SSL_CTX *ctx = NULL;
 
     if (!PyArg_ParseTupleAndKeywords(
@@ -1782,8 +1783,10 @@ context_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 #endif
     /* Defaults */
     SSL_CTX_set_verify(self->ctx, SSL_VERIFY_NONE, NULL);
-    SSL_CTX_set_options(self->ctx,
-                        SSL_OP_ALL & ~SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS);
+    options = SSL_OP_ALL & ~SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS;
+    if (proto_version != PY_SSL_VERSION_SSL2)
+        options |= SSL_OP_NO_SSLv2;
+    SSL_CTX_set_options(self->ctx, options);
 
 #define SID_CTX "Python"
     SSL_CTX_set_session_id_context(self->ctx, (const unsigned char *) SID_CTX,