diff --git a/Lib/test/nullbytecert.pem b/Lib/test/nullbytecert.pem
new file mode 100644
index 0000000..447186c
--- /dev/null
+++ b/Lib/test/nullbytecert.pem
@@ -0,0 +1,90 @@
+Certificate:
+    Data:
+        Version: 3 (0x2)
+        Serial Number: 0 (0x0)
+    Signature Algorithm: sha1WithRSAEncryption
+        Issuer: C=US, ST=Oregon, L=Beaverton, O=Python Software Foundation, OU=Python Core Development, CN=null.python.org\x00example.org/emailAddress=python-dev@python.org
+        Validity
+            Not Before: Aug  7 13:11:52 2013 GMT
+            Not After : Aug  7 13:12:52 2013 GMT
+        Subject: C=US, ST=Oregon, L=Beaverton, O=Python Software Foundation, OU=Python Core Development, CN=null.python.org\x00example.org/emailAddress=python-dev@python.org
+        Subject Public Key Info:
+            Public Key Algorithm: rsaEncryption
+                Public-Key: (2048 bit)
+                Modulus:
+                    00:b5:ea:ed:c9:fb:46:7d:6f:3b:76:80:dd:3a:f3:
+                    03:94:0b:a7:a6:db:ec:1d:df:ff:23:74:08:9d:97:
+                    16:3f:a3:a4:7b:3e:1b:0e:96:59:25:03:a7:26:e2:
+                    88:a9:cf:79:cd:f7:04:56:b0:ab:79:32:6e:59:c1:
+                    32:30:54:eb:58:a8:cb:91:f0:42:a5:64:27:cb:d4:
+                    56:31:88:52:ad:cf:bd:7f:f0:06:64:1f:cc:27:b8:
+                    a3:8b:8c:f3:d8:29:1f:25:0b:f5:46:06:1b:ca:02:
+                    45:ad:7b:76:0a:9c:bf:bb:b9:ae:0d:16:ab:60:75:
+                    ae:06:3e:9c:7c:31:dc:92:2f:29:1a:e0:4b:0c:91:
+                    90:6c:e9:37:c5:90:d7:2a:d7:97:15:a3:80:8f:5d:
+                    7b:49:8f:54:30:d4:97:2c:1c:5b:37:b5:ab:69:30:
+                    68:43:d3:33:78:4b:02:60:f5:3c:44:80:a1:8f:e7:
+                    f0:0f:d1:5e:87:9e:46:cf:62:fc:f9:bf:0c:65:12:
+                    f1:93:c8:35:79:3f:c8:ec:ec:47:f5:ef:be:44:d5:
+                    ae:82:1e:2d:9a:9f:98:5a:67:65:e1:74:70:7c:cb:
+                    d3:c2:ce:0e:45:49:27:dc:e3:2d:d4:fb:48:0e:2f:
+                    9e:77:b8:14:46:c0:c4:36:ca:02:ae:6a:91:8c:da:
+                    2f:85
+                Exponent: 65537 (0x10001)
+        X509v3 extensions:
+            X509v3 Basic Constraints: critical
+                CA:FALSE
+            X509v3 Subject Key Identifier:
+                88:5A:55:C0:52:FF:61:CD:52:A3:35:0F:EA:5A:9C:24:38:22:F7:5C
+            X509v3 Key Usage:
+                Digital Signature, Non Repudiation, Key Encipherment
+            X509v3 Subject Alternative Name:
+                *************************************************************
+                WARNING: The values for DNS, email and URI are WRONG. OpenSSL
+                         doesn't print the text after a NULL byte.
+                *************************************************************
+                DNS:altnull.python.org, email:null@python.org, URI:http://null.python.org, IP Address:192.0.2.1, IP Address:2001:DB8:0:0:0:0:0:1
+    Signature Algorithm: sha1WithRSAEncryption
+         ac:4f:45:ef:7d:49:a8:21:70:8e:88:59:3e:d4:36:42:70:f5:
+         a3:bd:8b:d7:a8:d0:58:f6:31:4a:b1:a4:a6:dd:6f:d9:e8:44:
+         3c:b6:0a:71:d6:7f:b1:08:61:9d:60:ce:75:cf:77:0c:d2:37:
+         86:02:8d:5e:5d:f9:0f:71:b4:16:a8:c1:3d:23:1c:f1:11:b3:
+         56:6e:ca:d0:8d:34:94:e6:87:2a:99:f2:ae:ae:cc:c2:e8:86:
+         de:08:a8:7f:c5:05:fa:6f:81:a7:82:e6:d0:53:9d:34:f4:ac:
+         3e:40:fe:89:57:7a:29:a4:91:7e:0b:c6:51:31:e5:10:2f:a4:
+         60:76:cd:95:51:1a:be:8b:a1:b0:fd:ad:52:bd:d7:1b:87:60:
+         d2:31:c7:17:c4:18:4f:2d:08:25:a3:a7:4f:b7:92:ca:e2:f5:
+         25:f1:54:75:81:9d:b3:3d:61:a2:f7:da:ed:e1:c6:6f:2c:60:
+         1f:d8:6f:c5:92:05:ab:c9:09:62:49:a9:14:ad:55:11:cc:d6:
+         4a:19:94:99:97:37:1d:81:5f:8b:cf:a3:a8:96:44:51:08:3d:
+         0b:05:65:12:eb:b6:70:80:88:48:72:4f:c6:c2:da:cf:cd:8e:
+         5b:ba:97:2f:60:b4:96:56:49:5e:3a:43:76:63:04:be:2a:f6:
+         c1:ca:a9:94
+-----BEGIN CERTIFICATE-----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=
+-----END CERTIFICATE-----
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 5c8df8b..d90e46d 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -52,6 +52,7 @@
 WRONGCERT = data_file("XXXnonexisting.pem")
 BADKEY = data_file("badkey.pem")
 NOKIACERT = data_file("nokia.pem")
+NULLBYTECERT = data_file("nullbytecert.pem")
 
 
 def handle_error(prefix):
@@ -140,6 +141,27 @@
                           ('DNS', 'projects.forum.nokia.com'))
                         )
 
+    def test_parse_cert_CVE_2013_4073(self):
+        p = ssl._ssl._test_decode_cert(NULLBYTECERT)
+        if support.verbose:
+            sys.stdout.write("\n" + pprint.pformat(p) + "\n")
+        subject = ((('countryName', 'US'),),
+                   (('stateOrProvinceName', 'Oregon'),),
+                   (('localityName', 'Beaverton'),),
+                   (('organizationName', 'Python Software Foundation'),),
+                   (('organizationalUnitName', 'Python Core Development'),),
+                   (('commonName', 'null.python.org\x00example.org'),),
+                   (('emailAddress', 'python-dev@python.org'),))
+        self.assertEqual(p['subject'], subject)
+        self.assertEqual(p['issuer'], subject)
+        self.assertEqual(p['subjectAltName'],
+                         (('DNS', 'altnull.python.org\x00example.com'),
+                         ('email', 'null@python.org\x00user@example.org'),
+                         ('URI', 'http://null.python.org\x00http://example.org'),
+                         ('IP Address', '192.0.2.1'),
+                         ('IP Address', '2001:DB8:0:0:0:0:0:1\n'))
+                        )
+
     def test_DER_to_PEM(self):
         with open(SVN_PYTHON_ORG_ROOT_CERT, 'r') as f:
             pem = f.read()
@@ -271,6 +293,13 @@
         fail(cert, 'foo.a.com')
         fail(cert, 'bar.foo.com')
 
+        # NULL bytes are bad, CVE-2013-4073
+        cert = {'subject': ((('commonName',
+                              'null.python.org\x00example.org'),),)}
+        ok(cert, 'null.python.org\x00example.org') # or raise an error?
+        fail(cert, 'example.org')
+        fail(cert, 'null.python.org')
+
         # Slightly fake real-world example
         cert = {'notAfter': 'Jun 26 21:41:46 2011 GMT',
                 'subject': ((('commonName', 'linuxfrz.org'),),),
diff --git a/Misc/NEWS b/Misc/NEWS
index 12f02b3..d239d69 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,12 @@
 Library
 -------
 
+- Issue #18709: Fix CVE-2013-4238. The SSL module now handles NULL bytes
+  inside subjectAltName correctly. Formerly the module has used OpenSSL's
+  GENERAL_NAME_print() function to get the string represention of ASN.1
+  strings for ``rfc822Name`` (email), ``dNSName`` (DNS) and
+  ``uniformResourceIdentifier`` (URI).
+
 - Issue #21766: Prevent a security hole in CGIHTTPServer by URL unquoting paths
   before checking for a CGI script at that path.
 
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index e9de8ca..e273c5c 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -561,7 +561,7 @@
 
     int i, j;
     PyObject *peer_alt_names = Py_None;
-    PyObject *v, *t;
+    PyObject *v = NULL, *t;
     X509_EXTENSION *ext = NULL;
     GENERAL_NAMES *names = NULL;
     GENERAL_NAME *name;
@@ -616,12 +616,14 @@
                            ext->value->length));
 
         for(j = 0; j < sk_GENERAL_NAME_num(names); j++) {
-
             /* get a rendering of each name in the set of names */
+            int gntype;
+            ASN1_STRING *as = NULL;
 
             name = sk_GENERAL_NAME_value(names, j);
-            if (name->type == GEN_DIRNAME) {
-
+            gntype = name-> type;
+            switch (gntype) {
+            case GEN_DIRNAME:
                 /* we special-case DirName as a tuple of
                    tuples of attributes */
 
@@ -643,11 +645,62 @@
                     goto fail;
                 }
                 PyTuple_SET_ITEM(t, 1, v);
+                break;
 
-            } else {
+            case GEN_EMAIL:
+            case GEN_DNS:
+            case GEN_URI:
+                /* GENERAL_NAME_print() doesn't handle NUL bytes in ASN1_string
+                   correctly. */
+                t = PyTuple_New(2);
+                if (t == NULL)
+                    goto fail;
+                switch (gntype) {
+                case GEN_EMAIL:
+                    v = PyUnicode_FromString("email");
+                    as = name->d.rfc822Name;
+                    break;
+                case GEN_DNS:
+                    v = PyUnicode_FromString("DNS");
+                    as = name->d.dNSName;
+                    break;
+                case GEN_URI:
+                    v = PyUnicode_FromString("URI");
+                    as = name->d.uniformResourceIdentifier;
+                    break;
+                }
+                if (v == NULL) {
+                    Py_DECREF(t);
+                    goto fail;
+                }
+                PyTuple_SET_ITEM(t, 0, v);
+                v = PyUnicode_FromStringAndSize((char *)ASN1_STRING_data(as),
+                                                ASN1_STRING_length(as));
+                if (v == NULL) {
+                    Py_DECREF(t);
+                    goto fail;
+                }
+                PyTuple_SET_ITEM(t, 1, v);
+                break;
 
+            default:
                 /* for everything else, we use the OpenSSL print form */
-
+                switch (gntype) {
+                    /* check for new general name type */
+                    case GEN_OTHERNAME:
+                    case GEN_X400:
+                    case GEN_EDIPARTY:
+                    case GEN_IPADD:
+                    case GEN_RID:
+                        break;
+                    default:
+                        if (PyErr_WarnFormat(PyExc_RuntimeWarning, 1,
+                                             "Unknown general name type %d",
+                                             gntype) == -1) {
+                            goto fail;
+                        }
+                        break;
+                }
                 (void) BIO_reset(biobuf);
                 GENERAL_NAME_print(biobuf, name);
                 len = BIO_gets(biobuf, buf, sizeof(buf)-1);
@@ -674,6 +727,7 @@
                     goto fail;
                 }
                 PyTuple_SET_ITEM(t, 1, v);
+                break;
             }
 
             /* and add that rendering to the list */