From b15f8769644b00ef7283521593360b7b2135cb63 Mon Sep 17 00:00:00 2001
From: "Dr. Stephen Henson" <steve@openssl.org>
Date: Fri, 24 Oct 2014 12:30:33 +0100
Subject: [PATCH] ECDH downgrade bug fix.

Fix bug where an OpenSSL client would accept a handshake using an
ephemeral ECDH ciphersuites with the server key exchange message omitted.

Thanks to Karthikeyan Bhargavan for reporting this issue.

CVE-2014-3572
Reviewed-by: Matt Caswell <matt@openssl.org>
---
 CHANGES       |  7 +++++++
 ssl/s3_clnt.c | 18 +++++++++++++++---
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/CHANGES b/CHANGES
index c444b24a2c..0252eb5706 100644
--- a/CHANGES
+++ b/CHANGES
@@ -659,6 +659,13 @@
 
  Changes between 1.0.1j and 1.0.1k [xx XXX xxxx]
 
+  *) Abort handshake if server key exchange message is omitted for ephemeral
+     ECDH ciphersuites.
+
+     Thanks to Karthikeyan Bhargavan for reporting this issue.
+     (CVE-2014-3572)
+     [Steve Henson]
+
   *) Ensure that the session ID context of an SSL is updated when its
      SSL_CTX is updated via SSL_set_SSL_CTX.
 
diff --git a/ssl/s3_clnt.c b/ssl/s3_clnt.c
index 4ca2774f23..2313fbc1e7 100644
--- a/ssl/s3_clnt.c
+++ b/ssl/s3_clnt.c
@@ -1376,6 +1376,8 @@ int ssl3_get_key_exchange(SSL *s)
 	int encoded_pt_len = 0;
 #endif
 
+	EVP_MD_CTX_init(&md_ctx);
+
 	/* use same message size as in ssl3_get_certificate_request()
 	 * as ServerKeyExchange message may be skipped */
 	n=s->method->ssl_get_message(s,
@@ -1386,14 +1388,26 @@ int ssl3_get_key_exchange(SSL *s)
 		&ok);
 	if (!ok) return((int)n);
 
+	alg_k=s->s3->tmp.new_cipher->algorithm_mkey;
+
 	if (s->s3->tmp.message_type != SSL3_MT_SERVER_KEY_EXCHANGE)
 		{
+		/*
+		 * Can't skip server key exchange if this is an ephemeral
+		 * ciphersuite.
+		 */
+		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;
+			}
 #ifndef OPENSSL_NO_PSK
 		/* In plain PSK ciphersuite, ServerKeyExchange can be
 		   omitted if no identity hint is sent. Set
 		   session->sess_cert anyway to avoid problems
 		   later.*/
-		if (s->s3->tmp.new_cipher->algorithm_mkey & SSL_kPSK)
+		if (alg_k & SSL_kPSK)
 			{
 			s->session->sess_cert=ssl_sess_cert_new();
 			if (s->ctx->psk_identity_hint)
@@ -1438,9 +1452,7 @@ int ssl3_get_key_exchange(SSL *s)
 	/* Total length of the parameters including the length prefix */
 	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);
 
 	al=SSL_AD_DECODE_ERROR;
 
-- 
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