Reject DH keys sent by a server if they are considered too small; inspired

by a similar BoringSSL change, but raising the limit to 1024 bits.
ok jsing@ markus@ guenther@ deraadt@

2 files changed, 24 insertions, 2 deletions

diff --git a/src/lib/libssl/s3_clnt.c b/src/lib/libssl/s3_clnt.c
index 9b52691015..d68aecf541 100644
--- a/src/lib/libssl/s3_clnt.c
+++ b/src/lib/libssl/s3_clnt.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: s3_clnt.c,v 1.107 2015/02/07 05:46:01 jsing Exp $ */
+/* $OpenBSD: s3_clnt.c,v 1.108 2015/03/08 16:48:47 miod Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -1268,6 +1268,17 @@ ssl3_get_key_exchange(SSL *s)
                 p += i;
                 n -= param_len;
 
+                /*
+                 * Check the strength of the DH key just constructed.
+                 * Discard keys weaker than 1024 bits.
+                 */
+
+                if (DH_size(dh) < 1024 / 8) {
+                        SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
+                            SSL_R_BAD_DH_P_LENGTH);
+                        goto err;
+                }
+
                 if (alg_a & SSL_aRSA)
                         pkey = X509_get_pubkey(
                             s->session->sess_cert->peer_pkeys[
diff --git a/src/lib/libssl/src/ssl/s3_clnt.c b/src/lib/libssl/src/ssl/s3_clnt.c
index 9b52691015..d68aecf541 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 1.107 2015/02/07 05:46:01 jsing Exp $ */
+/* $OpenBSD: s3_clnt.c,v 1.108 2015/03/08 16:48:47 miod Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -1268,6 +1268,17 @@ ssl3_get_key_exchange(SSL *s)
                 p += i;
                 n -= param_len;
 
+                /*
+                 * Check the strength of the DH key just constructed.
+                 * Discard keys weaker than 1024 bits.
+                 */
+
+                if (DH_size(dh) < 1024 / 8) {
+                        SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,
+                            SSL_R_BAD_DH_P_LENGTH);
+                        goto err;
+                }
+
                 if (alg_a & SSL_aRSA)
                         pkey = X509_get_pubkey(
                             s->session->sess_cert->peer_pkeys[