Enforce secure renegotiation support by default

Previously we would set SSL_OP_LEGACY_SERVER_CONNECT by default in
SSL_CTX_new(), to allow connections to legacy servers that did not
implement RFC 5746.

It has been more than a decade since RFC 5746 was published, so
there has been plenty of time for implmentation support to roll out.

Change the default behavior to be to require peers to support
secure renegotiation.  Existing applications that already cleared
SSL_OP_LEGACY_SERVER_CONNECT will see no behavior change, as
re-clearing the flag is just a little bit of redundant work.
The old behavior is still available by explicitly setting the flag
in the application.

Also remove SSL_OP_LEGACY_SERVER_CONNECT from SSL_OP_ALL, for
similar reasons.

Document the behavior change in CHANGES.md, and update the
SSL_CTX_set_options() and SSL_CONF_cmd manuals to reflect the change
in default behavior.

Fixes: 14848

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15127)

CHANGES.md

@@ -82,6 +82,14 @@ OpenSSL 3.0
 
    *Boris Pismenny, John Baldwin and Andrew Gallatin*
 
+ * Support for RFC 5746 secure renegotiation is now required by default for
+   SSL or TLS connections to succeed.  Applications that require the ability
+   to connect to legacy peers will need to explicitly set
+   SSL_OP_LEGACY_SERVER_CONNECT.  Accordingly, SSL_OP_LEGACY_SERVER_CONNECT
+   is no longer set as part of SSL_OP_ALL.
+
+   *Benjamin Kaduk*
+
  * The signature of the `copy` functional parameter of the
    EVP_PKEY_meth_set_copy() function has changed so its `src` argument is
    now `const EVP_PKEY_CTX *` instead of `EVP_PKEY_CTX *`. Similarly

doc/man3/SSL_CONF_cmd.pod

@@ -76,7 +76,6 @@ set SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION flag. Only used by servers.
 
 permits or prohibits the use of unsafe legacy renegotiation for OpenSSL
 clients only. Equivalent to setting or clearing B<SSL_OP_LEGACY_SERVER_CONNECT>.
-Set by default.
 
 =item B<-prioritize_chacha>
 

doc/man3/SSL_CTX_set_options.pod

@@ -88,8 +88,7 @@ implementations.
 
 =item SSL_OP_ALL
 
-All of the above bug workarounds plus B<SSL_OP_LEGACY_SERVER_CONNECT> as
-mentioned below.
+All of the above bug workarounds.
 
 =back
 
@@ -193,8 +192,7 @@ servers. See the B<SECURE RENEGOTIATION> section for more details.
 =item SSL_OP_LEGACY_SERVER_CONNECT
 
 Allow legacy insecure renegotiation between OpenSSL and unpatched servers
-B<only>: this option is currently set by default. See the
-B<SECURE RENEGOTIATION> section for more details.
+B<only>. See the B<SECURE RENEGOTIATION> section for more details.
 
 =item SSL_OP_NO_ENCRYPT_THEN_MAC
 
@@ -378,15 +376,10 @@ and renegotiation between patched OpenSSL clients and unpatched servers
 succeeds. If neither option is set then initial connections to unpatched
 servers will fail.
 
-The option B<SSL_OP_LEGACY_SERVER_CONNECT> is currently set by default even
-though it has security implications: otherwise it would be impossible to
-connect to unpatched servers (i.e. all of them initially) and this is clearly
-not acceptable. Renegotiation is permitted because this does not add any
-additional security issues: during an attack clients do not see any
-renegotiations anyway.
-
-As more servers become patched the option B<SSL_OP_LEGACY_SERVER_CONNECT> will
-B<not> be set by default in a future version of OpenSSL.
+Setting the option B<SSL_OP_LEGACY_SERVER_CONNECT> has security implications;
+clients that are willing to connect to servers that do not implement
+RFC 5746 secure renegotiation are subject to attacks such as
+CVE-2009-3555.
 
 OpenSSL client applications wishing to ensure they can connect to unpatched
 servers should always B<set> B<SSL_OP_LEGACY_SERVER_CONNECT>

include/openssl/ssl.h.in

@@ -425,7 +425,6 @@ typedef int (*SSL_async_callback_fn)(SSL *s, void *arg);
  */
 # define SSL_OP_ALL        (SSL_OP_CRYPTOPRO_TLSEXT_BUG|\
                             SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS|\
-                            SSL_OP_LEGACY_SERVER_CONNECT|\
                             SSL_OP_TLSEXT_PADDING|\
                             SSL_OP_SAFARI_ECDHE_ECDSA_BUG)
 

ssl/ssl_lib.c

@@ -3310,11 +3310,6 @@ SSL_CTX *SSL_CTX_new_ex(OSSL_LIB_CTX *libctx, const char *propq,
     }
 # endif
 #endif
-    /*
-     * Default is to connect to non-RI servers. When RI is more widely
-     * deployed might change this.
-     */
-    ret->options |= SSL_OP_LEGACY_SERVER_CONNECT;
     /*
      * Disable compression by default to prevent CRIME. Applications can
      * re-enable compression by configuring