Issue 28043: SSLContext has improved default settings
The options OP_NO_COMPRESSION, OP_CIPHER_SERVER_PREFERENCE, OP_SINGLE_DH_USE, OP_SINGLE_ECDH_USE, OP_NO_SSLv2 (except for PROTOCOL_SSLv2), and OP_NO_SSLv3 (except for PROTOCOL_SSLv3) are set by default. The initial cipher suite list contains only HIGH ciphers, no NULL ciphers and MD5 ciphers (except for PROTOCOL_SSLv2).
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index b4fac44..d605405 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -2407,6 +2407,7 @@
PySSLContext *self;
long options;
SSL_CTX *ctx = NULL;
+ int result;
#if defined(SSL_MODE_RELEASE_BUFFERS)
unsigned long libver;
#endif
@@ -2470,8 +2471,38 @@
options |= SSL_OP_NO_SSLv2;
if (proto_version != PY_SSL_VERSION_SSL3)
options |= SSL_OP_NO_SSLv3;
+ /* Minimal security flags for server and client side context.
+ * Client sockets ignore server-side parameters. */
+#ifdef SSL_OP_NO_COMPRESSION
+ options |= SSL_OP_NO_COMPRESSION;
+#endif
+#ifdef SSL_OP_CIPHER_SERVER_PREFERENCE
+ options |= SSL_OP_CIPHER_SERVER_PREFERENCE;
+#endif
+#ifdef SSL_OP_SINGLE_DH_USE
+ options |= SSL_OP_SINGLE_DH_USE;
+#endif
+#ifdef SSL_OP_SINGLE_ECDH_USE
+ options |= SSL_OP_SINGLE_ECDH_USE;
+#endif
SSL_CTX_set_options(self->ctx, options);
+ /* A bare minimum cipher list without completly broken cipher suites.
+ * It's far from perfect but gives users a better head start. */
+ if (proto_version != PY_SSL_VERSION_SSL2) {
+ result = SSL_CTX_set_cipher_list(ctx, "HIGH:!aNULL:!eNULL:!MD5");
+ } else {
+ /* SSLv2 needs MD5 */
+ result = SSL_CTX_set_cipher_list(ctx, "HIGH:!aNULL:!eNULL");
+ }
+ if (result == 0) {
+ Py_DECREF(self);
+ ERR_clear_error();
+ PyErr_SetString(PySSLErrorObject,
+ "No cipher can be selected.");
+ return NULL;
+ }
+
#if defined(SSL_MODE_RELEASE_BUFFERS)
/* Set SSL_MODE_RELEASE_BUFFERS. This potentially greatly reduces memory
usage for no cost at all. However, don't do this for OpenSSL versions