Ensure that a ServerKeyExchange message is received if the selected cipher

suite uses ephemeral keys. This avoids an issue where an ECHDE cipher suite can
effectively be downgraded to ECDH, if the server omits the ServerKeyExchange
message and has provided a certificate with an ECC public key.

Issue reported to OpenSSL by Karthikeyan Bhargavan.

Based on OpenSSL.

Fixes CVE-2014-3572.

ok beck@

2 files changed, 36 insertions, 10 deletions

diff --git a/src/lib/libssl/s3_clnt.c b/src/lib/libssl/s3_clnt.c
index d1f2e05eb8..b1c8ffb200 100644
--- a/src/lib/libssl/s3_clnt.c
+++ b/src/lib/libssl/s3_clnt.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: s3_clnt.c,v 1.103 2014/12/15 00:46:53 doug Exp $ */
+/* $OpenBSD: s3_clnt.c,v 1.104 2015/01/23 14:40:59 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -1165,6 +1165,11 @@ ssl3_get_key_exchange(SSL *s)
         int              curve_nid = 0;
         int              encoded_pt_len = 0;
 
+        alg_k = s->s3->tmp.new_cipher->algorithm_mkey;
+        alg_a = s->s3->tmp.new_cipher->algorithm_auth;
+
+        EVP_MD_CTX_init(&md_ctx);
+
         /*
          * Use same message size as in ssl3_get_certificate_request()
          * as ServerKeyExchange message may be skipped.
@@ -1175,11 +1180,21 @@ ssl3_get_key_exchange(SSL *s)
                 return ((int)n);
 
         if (s->s3->tmp.message_type != SSL3_MT_SERVER_KEY_EXCHANGE) {
+                /*
+                 * Do not skip server key exchange if this cipher suite uses
+                 * ephemeral keys.
+                 */
+                if (alg_k & (SSL_kDHE|SSL_kECDHE)) {
+                        SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
+                            SSL_R_UNEXPECTED_MESSAGE);
+                        al = SSL_AD_UNEXPECTED_MESSAGE;
+                        goto f_err;
+                }
+
                 s->s3->tmp.reuse_message = 1;
                 return (1);
         }
 
-        param = p = (unsigned char *)s->init_msg;
         if (s->session->sess_cert != NULL) {
                 DH_free(s->session->sess_cert->peer_dh_tmp);
                 s->session->sess_cert->peer_dh_tmp = NULL;
@@ -1192,10 +1207,8 @@ ssl3_get_key_exchange(SSL *s)
                         goto err;
         }
 
+        param = p = (unsigned char *)s->init_msg;
         param_len = 0;
-        alg_k = s->s3->tmp.new_cipher->algorithm_mkey;
-        alg_a = s->s3->tmp.new_cipher->algorithm_auth;
-        EVP_MD_CTX_init(&md_ctx);
 
         if (alg_k & SSL_kDHE) {
                 if ((dh = DH_new()) == NULL) {
diff --git a/src/lib/libssl/src/ssl/s3_clnt.c b/src/lib/libssl/src/ssl/s3_clnt.c
index d1f2e05eb8..b1c8ffb200 100644
--- a/src/lib/libssl/src/ssl/s3_clnt.c
+++ b/src/lib/libssl/src/ssl/s3_clnt.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: s3_clnt.c,v 1.103 2014/12/15 00:46:53 doug Exp $ */
+/* $OpenBSD: s3_clnt.c,v 1.104 2015/01/23 14:40:59 jsing Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -1165,6 +1165,11 @@ ssl3_get_key_exchange(SSL *s)
         int              curve_nid = 0;
         int              encoded_pt_len = 0;
 
+        alg_k = s->s3->tmp.new_cipher->algorithm_mkey;
+        alg_a = s->s3->tmp.new_cipher->algorithm_auth;
+
+        EVP_MD_CTX_init(&md_ctx);
+
         /*
          * Use same message size as in ssl3_get_certificate_request()
          * as ServerKeyExchange message may be skipped.
@@ -1175,11 +1180,21 @@ ssl3_get_key_exchange(SSL *s)
                 return ((int)n);
 
         if (s->s3->tmp.message_type != SSL3_MT_SERVER_KEY_EXCHANGE) {
+                /*
+                 * Do not skip server key exchange if this cipher suite uses
+                 * ephemeral keys.
+                 */
+                if (alg_k & (SSL_kDHE|SSL_kECDHE)) {
+                        SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
+                            SSL_R_UNEXPECTED_MESSAGE);
+                        al = SSL_AD_UNEXPECTED_MESSAGE;
+                        goto f_err;
+                }
+
                 s->s3->tmp.reuse_message = 1;
                 return (1);
         }
 
-        param = p = (unsigned char *)s->init_msg;
         if (s->session->sess_cert != NULL) {
                 DH_free(s->session->sess_cert->peer_dh_tmp);
                 s->session->sess_cert->peer_dh_tmp = NULL;
@@ -1192,10 +1207,8 @@ ssl3_get_key_exchange(SSL *s)
                         goto err;
         }
 
+        param = p = (unsigned char *)s->init_msg;
         param_len = 0;
-        alg_k = s->s3->tmp.new_cipher->algorithm_mkey;
-        alg_a = s->s3->tmp.new_cipher->algorithm_auth;
-        EVP_MD_CTX_init(&md_ctx);
 
         if (alg_k & SSL_kDHE) {
                 if ((dh = DH_new()) == NULL) {