commit 485b3930c93da4e0dc5d291ca94b89c434bb9bb5
author Angus Gratton <angus@espressif.com> Tue Jun 19 15:58:22 2018 +1000
committer Andres Amaya Garcia <Andres.AmayaGarcia@arm.com> Mon Jul 16 20:20:49 2018 +0100
tree fff363a3c2437d5167bfb0264f1c24e5a9979814
parent 1226dd7715f86898a45823c88b924047dcd1263a

TLSv1.2: Treat zero-length fragments as invalid, unless they are application data

TLS v1.2 explicitly disallows other kinds of zero length fragments (earlier standards
don't mention zero-length fragments at all).

library/ssl_tls.c

diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index d751aa3..03600f8 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -2034,6 +2034,16 @@
 
     if( ssl->in_msglen == 0 )
     {
+#if defined(MBEDTLS_SSL_PROTO_TLS1_2)
+        if( ssl->minor_ver == MBEDTLS_SSL_MINOR_VERSION_3
+            && ssl->in_msgtype != MBEDTLS_SSL_MSG_APPLICATION_DATA )
+        {
+            /* TLS v1.2 explicitly disallows zero-length messages which are not application data */
+            MBEDTLS_SSL_DEBUG_MSG( 1, ( "invalid zero-length message type: %d", ssl->in_msgtype ) );
+            return( MBEDTLS_ERR_SSL_INVALID_RECORD );
+        }
+#endif /* MBEDTLS_SSL_PROTO_TLS1_2 */
+
         ssl->nb_zero++;
 
         /*