From e284402f0daf496a00e4c274802abb7972adb36c Mon Sep 17 00:00:00 2001
From: djm <djm@openbsd.org>
Date: Sun, 31 May 2026 06:14:42 +0000
Subject: [PATCH] avoid strlen(NULL) crash if an X11 channel was created before
 the x11-req SSH_MSG_CHANNEL_REQUEST was sent. Reported by Ben Perry via
 GHPR679

---
 usr.bin/ssh/channels.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/usr.bin/ssh/channels.c b/usr.bin/ssh/channels.c
index 712e816dadb..7c563c48fb2 100644
--- a/usr.bin/ssh/channels.c
+++ b/usr.bin/ssh/channels.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: channels.c,v 1.459 2026/04/20 07:43:52 job Exp $ */
+/* $OpenBSD: channels.c,v 1.460 2026/05/31 06:14:42 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -1370,6 +1370,11 @@ x11_open_helper(struct ssh *ssh, struct sshbuf *b)
 	u_char *ucp;
 	u_int proto_len, data_len;
 
+	if (sc->x11_saved_proto == NULL) {
+		error("X11 forwarding opened before X11 forwarding requested");
+		return -1;
+	}
+
 	/* Is this being called after the refusal deadline? */
 	if (sc->x11_refuse_time != 0 &&
 	    monotime() >= sc->x11_refuse_time) {