bpo-33136: Harden ssl module against CVE-2018-8970 (GH-6229)

tiran · web-flow · commit d02ac25ab087 · 2018-03-25T12:36:13.000+02:00
Harden ssl module against LibreSSL CVE-2018-8970. X509_VERIFY_PARAM_set1_host() is called with an explicit namelen. A new test ensures that NULL bytes are not allowed. Signed-off-by: Christian Heimes <christian@python.org>
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
@@ -1660,6 +1660,9 @@ def test_bad_server_hostname(self):
         with self.assertRaises(ValueError):
             ctx.wrap_bio(ssl.MemoryBIO(), ssl.MemoryBIO(),
                          server_hostname=".example.org")
+        with self.assertRaises(TypeError):
+            ctx.wrap_bio(ssl.MemoryBIO(), ssl.MemoryBIO(),
+                         server_hostname="example.org\x00evil.com")
 
 
 class MemoryBIOTests(unittest.TestCase):
diff --git a/Misc/NEWS.d/next/Security/2018-03-25-12-05-43.bpo-33136.TzSN4x.rst b/Misc/NEWS.d/next/Security/2018-03-25-12-05-43.bpo-33136.TzSN4x.rst
@@ -0,0 +1,3 @@
+Harden ssl module against LibreSSL CVE-2018-8970.
+X509_VERIFY_PARAM_set1_host() is called with an explicit namelen. A new test
+ensures that NULL bytes are not allowed.
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
@@ -852,7 +852,8 @@ _ssl_configure_hostname(PySSLSocket *self, const char* server_hostname)
     if (self->ctx->check_hostname) {
         X509_VERIFY_PARAM *param = SSL_get0_param(self->ssl);
         if (ip == NULL) {
-            if (!X509_VERIFY_PARAM_set1_host(param, server_hostname, 0)) {
+            if (!X509_VERIFY_PARAM_set1_host(param, server_hostname,
+                                             strlen(server_hostname))) {
                 _setSSLError(NULL, 0, __FILE__, __LINE__);
                 goto error;
             }
@@ -4025,7 +4026,7 @@ _ssl__SSLContext__wrap_socket_impl(PySSLContext *self, PyObject *sock,
     PyObject *res;
 
     /* server_hostname is either None (or absent), or to be encoded
-       as IDN A-label (ASCII str). */
+       as IDN A-label (ASCII str) without NULL bytes. */
     if (hostname_obj != Py_None) {
         if (!PyArg_Parse(hostname_obj, "es", "ascii", &hostname))
             return NULL;
@@ -4063,7 +4064,7 @@ _ssl__SSLContext__wrap_bio_impl(PySSLContext *self, PySSLMemoryBIO *incoming,
     PyObject *res;
 
     /* server_hostname is either None (or absent), or to be encoded
-       as IDN A-label (ASCII str). */
+       as IDN A-label (ASCII str) without NULL bytes. */
     if (hostname_obj != Py_None) {
         if (!PyArg_Parse(hostname_obj, "es", "ascii", &hostname))
             return NULL;

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+Harden ssl module against LibreSSL CVE-2018-8970.`
	`2`	`+X509_VERIFY_PARAM_set1_host() is called with an explicit namelen. A new test`
	`3`	`+ensures that NULL bytes are not allowed.`