From d0a2a4304e8bc55b8e532933c8af4982563b033b Mon Sep 17 00:00:00 2001 From: beck <> Date: Thu, 23 Jan 2020 07:30:55 +0000 Subject: Add checking int the client to check the magic values which are set by a 1.3 server when it downgrades to tls 1.2 or 1.1 as per RFC 8446 section 4.1.3 ok jsing@ --- src/lib/libssl/tls13_client.c | 18 +++++++++++++++++- src/lib/libssl/tls13_internal.h | 5 ++++- src/lib/libssl/tls13_lib.c | 10 +++++++++- 3 files changed, 30 insertions(+), 3 deletions(-) (limited to 'src/lib') diff --git a/src/lib/libssl/tls13_client.c b/src/lib/libssl/tls13_client.c index cab113b8c3..477cca2e04 100644 --- a/src/lib/libssl/tls13_client.c +++ b/src/lib/libssl/tls13_client.c @@ -1,4 +1,4 @@ -/* $OpenBSD: tls13_client.c,v 1.30 2020/01/23 06:15:44 beck Exp $ */ +/* $OpenBSD: tls13_client.c,v 1.31 2020/01/23 07:30:55 beck Exp $ */ /* * Copyright (c) 2018, 2019 Joel Sing * @@ -285,6 +285,22 @@ tls13_server_hello_process(struct tls13_ctx *ctx, CBS *cbs) goto err; if (tls13_server_hello_is_legacy(cbs)) { + /* + * RFC 8446 section 4.1.3, We must not downgrade if + * the server random value contains the TLS 1.2 or 1.1 + * magical value. + */ + if (!CBS_skip(&server_random, CBS_len(&server_random) - + sizeof(tls13_downgrade_12))) + goto err; + if (CBS_mem_equal(&server_random, tls13_downgrade_12, + sizeof(tls13_downgrade_12)) || + CBS_mem_equal(&server_random, tls13_downgrade_11, + sizeof(tls13_downgrade_11))) { + ctx->alert = SSL_AD_ILLEGAL_PARAMETER; + goto err; + } + if (!CBS_skip(cbs, CBS_len(cbs))) goto err; return tls13_use_legacy_client(ctx); diff --git a/src/lib/libssl/tls13_internal.h b/src/lib/libssl/tls13_internal.h index 12ba5750a0..f11d96f2ea 100644 --- a/src/lib/libssl/tls13_internal.h +++ b/src/lib/libssl/tls13_internal.h @@ -1,4 +1,4 @@ -/* $OpenBSD: tls13_internal.h,v 1.48 2020/01/23 05:08:30 jsing Exp $ */ +/* $OpenBSD: tls13_internal.h,v 1.49 2020/01/23 07:30:55 beck Exp $ */ /* * Copyright (c) 2018 Bob Beck * Copyright (c) 2018 Theo Buehler @@ -305,6 +305,9 @@ int tls13_error_setx(struct tls13_error *error, int code, int subcode, tls13_error_setx(&(ctx)->error, (code), (subcode), __FILE__, __LINE__, \ (fmt), __VA_ARGS__) +extern uint8_t tls13_downgrade_12[8]; +extern uint8_t tls13_downgrade_11[8]; + __END_HIDDEN_DECLS #endif diff --git a/src/lib/libssl/tls13_lib.c b/src/lib/libssl/tls13_lib.c index de3e840a84..5d8c359014 100644 --- a/src/lib/libssl/tls13_lib.c +++ b/src/lib/libssl/tls13_lib.c @@ -1,4 +1,4 @@ -/* $OpenBSD: tls13_lib.c,v 1.23 2020/01/23 05:08:30 jsing Exp $ */ +/* $OpenBSD: tls13_lib.c,v 1.24 2020/01/23 07:30:55 beck Exp $ */ /* * Copyright (c) 2018, 2019 Joel Sing * Copyright (c) 2019 Bob Beck @@ -24,6 +24,14 @@ #include "ssl_locl.h" #include "tls13_internal.h" +/* + * RFC 8446 section 4.1.3, magic values which must be set by the + * server in server random if it is willing to downgrade but supports + * tls v1.3 + */ +uint8_t tls13_downgrade_12[8] = {0x44, 0x4f, 0x57, 0x4e, 0x47, 0x52, 0x44, 0x01}; +uint8_t tls13_downgrade_11[8] = {0x44, 0x4f, 0x57, 0x4e, 0x47, 0x52, 0x44, 0x00}; + const EVP_AEAD * tls13_cipher_aead(const SSL_CIPHER *cipher) { -- cgit v1.2.3-55-g6feb