From cf7a40bb11f97c00986c060585e3bc517ff3b9fb Mon Sep 17 00:00:00 2001
From: jsing <>
Date: Wed, 15 Jul 2026 15:00:17 +0000
Subject: Check that the server selected ciphersuite is valid for use with
 TLSv1.2.

In the legacy stack, ensure that the server selected ciphersuite is valid
for use with TLSv1.2 - this effectively means that it is not a TLSv1.3
ciphersuite. We currently fail the handshake, but at a later stage.

Reported by Tom Gouville from the tlspuffin team.

ok tb@
---
 src/lib/libssl/ssl_clnt.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

(limited to 'src/lib/libssl')

diff --git a/src/lib/libssl/ssl_clnt.c b/src/lib/libssl/ssl_clnt.c
index d9fdfff2a3..4803e35dd2 100644
--- a/src/lib/libssl/ssl_clnt.c
+++ b/src/lib/libssl/ssl_clnt.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_clnt.c,v 1.174 2026/07/15 13:56:38 jsing Exp $ */
+/* $OpenBSD: ssl_clnt.c,v 1.175 2026/07/15 15:00:17 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -1010,6 +1010,15 @@ ssl3_get_server_hello(SSL *s)
 		goto fatal_err;
 	}
 
+	/* Require a ciphersuite that can be used with TLSv1.2. */
+	if (cipher->algorithm_ssl != SSL_SSLV3 &&
+	    cipher->algorithm_ssl != SSL_TLSV1 &&
+	    cipher->algorithm_ssl != SSL_TLSV1_2) {
+		al = SSL_AD_ILLEGAL_PARAMETER;
+		SSLerror(s, SSL_R_WRONG_CIPHER_RETURNED);
+		goto fatal_err;
+	}
+
 	/*
 	 * Depending on the session caching (internal/external), the cipher
 	 * and/or cipher_id values may not be set. Make sure that
-- 
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