1 files changed, 9 insertions, 1 deletions

diff --git a/src/lib/libssl/tls13_client.c b/src/lib/libssl/tls13_client.c
index dbd5b0add7..d3a68528bc 100644
--- a/src/lib/libssl/tls13_client.c
+++ b/src/lib/libssl/tls13_client.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: tls13_client.c,v 1.59 2020/05/13 17:51:48 jsing Exp $ */
+/* $OpenBSD: tls13_client.c,v 1.60 2020/05/16 14:44:55 jsing Exp $ */
 /*
  * Copyright (c) 2018, 2019 Joel Sing <jsing@openbsd.org>
  *
@@ -595,6 +595,14 @@ tls13_server_certificate_recv(struct tls13_ctx *ctx, CBS *cbs)
                 cert = NULL;
         }
 
+        /* A server must always provide a non-empty certificate list. */
+        if (sk_X509_num(certs) < 1) {
+                ctx->alert = TLS13_ALERT_ILLEGAL_PARAMETER;
+                tls13_set_errorx(ctx, TLS13_ERR_NO_PEER_CERTIFICATE, 0,
+                    "peer failed to provide a certificate", NULL);
+                goto err;
+        }
+
         /*
          * At this stage we still have no proof of possession. As such, it would
          * be preferable to keep the chain and verify once we have successfully