Backout previous commit (intending that libressl client rejects a supported

groups extension from the server). It triggers 'CONNECT_CR_SRVR_HELLO:tlsv1
alert decode error' when connecting to a (modern) java server (tomcat 10.1.18
on openjdk 17.0.10).

"please revert" tb@

1 files changed, 17 insertions, 3 deletions

diff --git a/src/lib/libssl/ssl_tlsext.c b/src/lib/libssl/ssl_tlsext.c
index 6649baf291..90734457e5 100644
--- a/src/lib/libssl/ssl_tlsext.c
+++ b/src/lib/libssl/ssl_tlsext.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: ssl_tlsext.c,v 1.146 2024/03/28 00:22:35 beck Exp $ */
+/* $OpenBSD: ssl_tlsext.c,v 1.147 2024/04/02 22:50:54 sthen Exp $ */
 /*
  * Copyright (c) 2016, 2017, 2019 Joel Sing <jsing@openbsd.org>
  * Copyright (c) 2017 Doug Hogan <doug@openbsd.org>
@@ -324,8 +324,22 @@ static int
 tlsext_supportedgroups_client_process(SSL *s, uint16_t msg_type, CBS *cbs,
     int *alert)
 {
-        /* Servers should not send this extension per the RFC. */
-        return 0;
+        /*
+         * Servers should not send this extension per the RFC.
+         *
+         * However, certain F5 BIG-IP systems incorrectly send it. This bug is
+         * from at least 2014 but as of 2017, there are still large sites with
+         * this unpatched in production. As a result, we need to currently skip
+         * over the extension and ignore its content:
+         *
+         *  https://support.f5.com/csp/article/K37345003
+         */
+        if (!CBS_skip(cbs, CBS_len(cbs))) {
+                *alert = SSL_AD_INTERNAL_ERROR;
+                return 0;
+        }
+
+        return 1;
 }
 
 /*