commit 8315811ea78cd4ddbd564b8bfb98ec1c23a45dd8
author Glenn Strauss <gstrauss@gluelogic.com> Wed Apr 13 14:59:34 2022 -0400
committer Glenn Strauss <gstrauss@gluelogic.com> Thu Apr 14 15:40:14 2022 -0400
tree 146a735f46a4fe3bd3f71cbf06cb833c5a05acaf
parent bbdc83b55b2df836a6628631aa03c16d39e0a0d1

Remove restrictive proto ver negotiation checks

Overly restrictive protocol version negotiation checks might be
"version intolerant".  TLS 1.3 and DTLS 1.3 move the version to
the "supported_versions" ClientHello extension.

Signed-off-by: Glenn Strauss <gstrauss@gluelogic.com>

library/ssl_tls12_client.c

diff --git a/library/ssl_tls12_client.c b/library/ssl_tls12_client.c
index 8f5ab9b..d24e11f 100644
--- a/library/ssl_tls12_client.c
+++ b/library/ssl_tls12_client.c
@@ -1121,7 +1121,7 @@
 static int ssl_parse_hello_verify_request( mbedtls_ssl_context *ssl )
 {
     const unsigned char *p = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
-    mbedtls_ssl_protocol_version tls_version;
+    uint16_t dtls_legacy_version;
     unsigned char cookie_len;
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse hello verify request" ) );
@@ -1146,15 +1146,15 @@
      * } HelloVerifyRequest;
      */
     MBEDTLS_SSL_DEBUG_BUF( 3, "server version", p, 2 );
-    tls_version = mbedtls_ssl_read_version( p, ssl->conf->transport );
+    dtls_legacy_version = MBEDTLS_GET_UINT16_BE( p, 0 );
     p += 2;
 
     /*
-     * Since the RFC is not clear on this point, accept DTLS 1.0 (TLS 1.1)
-     * even if lower than our min version.
+     * Since the RFC is not clear on this point, accept DTLS 1.0 (0xfeff)
+     * The DTLS 1.3 (current draft) renames ProtocolVersion server_version to
+     * legacy_version and locks the value of legacy_version to 0xfefd (DTLS 1.2)
      */
-    if( tls_version < 0x0302 || /* TLSv1.1 */
-        tls_version > ssl->conf->max_tls_version )
+    if( dtls_legacy_version != 0xfefd && dtls_legacy_version != 0xfeff )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad server version" ) );
 

library/ssl_tls12_server.c

diff --git a/library/ssl_tls12_server.c b/library/ssl_tls12_server.c
index 9e3e736..e4d8148 100644
--- a/library/ssl_tls12_server.c
+++ b/library/ssl_tls12_server.c
@@ -1202,16 +1202,6 @@
     MBEDTLS_SSL_DEBUG_MSG( 3, ( "client hello, protocol version: [%d:%d]",
                    buf[1], buf[2] ) );
 
-    /* According to RFC 5246 Appendix E.1, the version here is typically
-     * "{03,00}, the lowest version number supported by the client, [or] the
-     * value of ClientHello.client_version", so the only meaningful check here
-     * is the major version shouldn't be less than 3 */
-    if( mbedtls_ssl_read_version( buf + 1, ssl->conf->transport ) < 0x0300 )
-    {
-        MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad client hello message" ) );
-        return( MBEDTLS_ERR_SSL_BAD_PROTOCOL_VERSION );
-    }
-
     /* For DTLS if this is the initial handshake, remember the client sequence
      * number to use it in our next message (RFC 6347 4.2.1) */
 #if defined(MBEDTLS_SSL_PROTO_DTLS)