Always duplicate the session on NewSessionTicket in TLSv1.3
Because NST messages arrive post-handshake, the session may have already
gone into the cache. Once in the cache a session must be immutable -
otherwise you could get multi-thread issues.
@@ -2438,7 +2438,15 @@ MSG_PROCESS_RETURN tls_process_new_session_ticket(SSL *s, PACKET *pkt)
if (ticklen == 0)
return MSG_PROCESS_CONTINUE_READING;
- if (s->session->session_id_length > 0) {
+ /*
+ * Sessions must be immutable once they go into the session cache. Otherwise
+ * we can get multi-thread problems. Therefore we don't "update" sessions,
+ * we replace them with a duplicate. In TLSv1.3 we need to do this every
+ * time a NewSessionTicket arrives because those messages arrive
+ * post-handshake and the session may have already gone into the session
+ * cache.
+ */
+ if (SSL_IS_TLS13(s) || s->session->session_id_length > 0) {
int i = s->session_ctx->session_cache_mode;
SSL_SESSION *new_sess;
/*
