From b7179c2a544f758dced616189c4a1cb4f7f01efd Mon Sep 17 00:00:00 2001
From: Sean Parkinson <sean@wolfssl.com>
Date: Mon, 4 Feb 2019 08:58:17 +1000
Subject: [PATCH] Disallow SupportedGroups in ServerHello for TLS 1.3

But allowed when downgrading to TLS 1.2.
---
 src/tls.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/tls.c b/src/tls.c
index 5813dbb9b..b314ee1e1 100644
--- a/src/tls.c
+++ b/src/tls.c
@@ -9654,6 +9654,11 @@ int TLSX_Parse(WOLFSSL* ssl, byte* input, word16 length, byte msgType,
                          msgType == encrypted_extensions) {
                     return EXT_NOT_ALLOWED;
                 }
+                else if (IsAtLeastTLSv1_3(ssl->ctx->method->version) &&
+                        msgType == server_hello &&
+                        !ssl->options.downgrade) {
+                    return EXT_NOT_ALLOWED;
+                }
 #endif
                 ret = EC_PARSE(ssl, input + offset, size, isRequest);
                 break;