From 6612a7181af32903b03020090fe361360142258b Mon Sep 17 00:00:00 2001

From: Nikos Mavrogiannopoulos <nmav@redhat.com>

Date: Wed, 9 Dec 2015 10:07:18 +0100

Subject: [PATCH] Prevent a downgrade attack to RSA-MD5 signatures

This is by considering the list of the signature algorithms set by

priorities.

---

 lib/ext/signature.c  |  18 +--

 tests/Makefile.am    |   2 +-

 tests/sign-md5-rep.c | 344 +++++++++++++++++++++++++++++++++++++++++++++++++++

 3 files changed, 346 insertions(+), 18 deletions(-)

 create mode 100644 tests/sign-md5-rep.c

diff --git a/lib/ext/signature.c b/lib/ext/signature.c

index fb971f5..6f3066e 100644

--- a/lib/ext/signature.c

+++ b/lib/ext/signature.c

@@ -313,28 +313,12 @@ _gnutls_session_sign_algo_enabled(gnutls_session_t session,

 				  gnutls_sign_algorithm_t sig)

 {

 	unsigned i;

-	int ret;

 	const version_entry_st *ver = get_version(session);

-	sig_ext_st *priv;

-	extension_priv_data_t epriv;

 	if (unlikely(ver == NULL))

 		return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

-	ret =

-	    _gnutls_ext_get_session_data(session,

-					 GNUTLS_EXTENSION_SIGNATURE_ALGORITHMS,

-					 &epriv);

-	if (ret < 0) {

-		gnutls_assert();

-		return 0;

-	}

-	priv = epriv.ptr;

-

-	if (!_gnutls_version_has_selectable_sighash(ver)

-	    || priv->sign_algorithms_size == 0)

-		/* none set, allow all */

-	{

+	if (!_gnutls_version_has_selectable_sighash(ver)) {

 		return 0;

 	}

diff --git a/tests/Makefile.am b/tests/Makefile.am

index 95d6541..d1c4839 100644

--- a/tests/Makefile.am

+++ b/tests/Makefile.am

@@ -84,7 +84,7 @@ ctests = mini-record-2 simple gc set_pkcs12_cred certder certuniqueid	\

 	 mini-cert-status mini-rsa-psk global-init sec-params \

 	 fips-test mini-global-load name-constraints x509-extensions \

 	 long-session-id mini-x509-callbacks-intr \

-	 crlverify init_fds

+	 crlverify init_fds sign-md5-rep

 if ENABLE_OCSP

 ctests += ocsp

diff --git a/tests/sign-md5-rep.c b/tests/sign-md5-rep.c

new file mode 100644

index 0000000..72869fa

--- /dev/null

+++ b/tests/sign-md5-rep.c

@@ -0,0 +1,344 @@

+/*

+ * Copyright (C) 2015 Nikos Mavrogiannopoulos

+ *

+ * Author: Nikos Mavrogiannopoulos

+ *

+ * This file is part of GnuTLS.

+ *

+ * GnuTLS is free software; you can redistribute it and/or modify it

+ * under the terms of the GNU General Public License as published by

+ * the Free Software Foundation; either version 3 of the License, or

+ * (at your option) any later version.

+ *

+ * GnuTLS is distributed in the hope that it will be useful, but

+ * WITHOUT ANY WARRANTY; without even the implied warranty of

+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

+ * General Public License for more details.

+ *

+ * You should have received a copy of the GNU General Public License

+ * along with GnuTLS; if not, write to the Free Software Foundation,

+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA

+ */

+

+#ifdef HAVE_CONFIG_H

+#include <config.h>

+#endif

+

+#include <stdio.h>

+#include <stdlib.h>

+

+#if defined(_WIN32)

+

+int main()

+{

+	exit(77);

+}

+

+#else

+

+#include <string.h>

+#include <sys/types.h>

+#include <netinet/in.h>

+#include <sys/socket.h>

+#include <sys/wait.h>

+#include <arpa/inet.h>

+#include <unistd.h>

+#include <gnutls/gnutls.h>

+#include <gnutls/dtls.h>

+#include <signal.h>

+

+#include "utils.h"

+

+static void terminate(void);

+

+/* This program tests whether EtM is negotiated as expected.

+ */

+

+static void server_log_func(int level, const char *str)

+{

+	fprintf(stderr, "server|<%d>| %s", level, str);

+}

+

+static void client_log_func(int level, const char *str)

+{

+	fprintf(stderr, "client|<%d>| %s", level, str);

+}

+

+static unsigned char server_cert_pem[] =

+    "-----BEGIN CERTIFICATE-----\n"

+    "MIICVjCCAcGgAwIBAgIERiYdMTALBgkqhkiG9w0BAQUwGTEXMBUGA1UEAxMOR251\n"

+    "VExTIHRlc3QgQ0EwHhcNMDcwNDE4MTMyOTIxWhcNMDgwNDE3MTMyOTIxWjA3MRsw\n"

+    "GQYDVQQKExJHbnVUTFMgdGVzdCBzZXJ2ZXIxGDAWBgNVBAMTD3Rlc3QuZ251dGxz\n"

+    "Lm9yZzCBnDALBgkqhkiG9w0BAQEDgYwAMIGIAoGA17pcr6MM8C6pJ1aqU46o63+B\n"

+    "dUxrmL5K6rce+EvDasTaDQC46kwTHzYWk95y78akXrJutsoKiFV1kJbtple8DDt2\n"

+    "DZcevensf9Op7PuFZKBroEjOd35znDET/z3IrqVgbtm2jFqab7a+n2q9p/CgMyf1\n"

+    "tx2S5Zacc1LWn9bIjrECAwEAAaOBkzCBkDAMBgNVHRMBAf8EAjAAMBoGA1UdEQQT\n"

+    "MBGCD3Rlc3QuZ251dGxzLm9yZzATBgNVHSUEDDAKBggrBgEFBQcDATAPBgNVHQ8B\n"

+    "Af8EBQMDB6AAMB0GA1UdDgQWBBTrx0Vu5fglyoyNgw106YbU3VW0dTAfBgNVHSME\n"

+    "GDAWgBTpPBz7rZJu5gakViyi4cBTJ8jylTALBgkqhkiG9w0BAQUDgYEAaFEPTt+7\n"

+    "bzvBuOf7+QmeQcn29kT6Bsyh1RHJXf8KTk5QRfwp6ogbp94JQWcNQ/S7YDFHglD1\n"

+    "AwUNBRXwd3riUsMnsxgeSDxYBfJYbDLeohNBsqaPDJb7XailWbMQKfAbFQ8cnOxg\n"

+    "rOKLUQRWJ0K3HyXRMhbqjdLIaQiCvQLuizo=\n" "-----END CERTIFICATE-----\n";

+

+const gnutls_datum_t server_cert = { server_cert_pem,

+	sizeof(server_cert_pem)

+};

+

+static unsigned char server_key_pem[] =

+    "-----BEGIN RSA PRIVATE KEY-----\n"

+    "MIICXAIBAAKBgQDXulyvowzwLqknVqpTjqjrf4F1TGuYvkrqtx74S8NqxNoNALjq\n"

+    "TBMfNhaT3nLvxqResm62ygqIVXWQlu2mV7wMO3YNlx696ex/06ns+4VkoGugSM53\n"

+    "fnOcMRP/PciupWBu2baMWppvtr6far2n8KAzJ/W3HZLllpxzUtaf1siOsQIDAQAB\n"

+    "AoGAYAFyKkAYC/PYF8e7+X+tsVCHXppp8AoP8TEZuUqOZz/AArVlle/ROrypg5kl\n"

+    "8YunrvUdzH9R/KZ7saNZlAPLjZyFG9beL/am6Ai7q7Ma5HMqjGU8kTEGwD7K+lbG\n"

+    "iomokKMOl+kkbY/2sI5Czmbm+/PqLXOjtVc5RAsdbgvtmvkCQQDdV5QuU8jap8Hs\n"

+    "Eodv/tLJ2z4+SKCV2k/7FXSKWe0vlrq0cl2qZfoTUYRnKRBcWxc9o92DxK44wgPi\n"

+    "oMQS+O7fAkEA+YG+K9e60sj1K4NYbMPAbYILbZxORDecvP8lcphvwkOVUqbmxOGh\n"

+    "XRmTZUuhBrJhJKKf6u7gf3KWlPl6ShKEbwJASC118cF6nurTjuLf7YKARDjNTEws\n"

+    "qZEeQbdWYINAmCMj0RH2P0mvybrsXSOD5UoDAyO7aWuqkHGcCLv6FGG+qwJAOVqq\n"

+    "tXdUucl6GjOKKw5geIvRRrQMhb/m5scb+5iw8A4LEEHPgGiBaF5NtJZLALgWfo5n\n"

+    "hmC8+G8F0F78znQtPwJBANexu+Tg5KfOnzSILJMo3oXiXhf5PqXIDmbN0BKyCKAQ\n"

+    "LfkcEcUbVfmDaHpvzwY9VEaoMOKVLitETXdNSxVpvWM=\n"

+    "-----END RSA PRIVATE KEY-----\n";

+

+const gnutls_datum_t server_key = { server_key_pem,

+	sizeof(server_key_pem)

+};

+

+

+static int handshake_callback(gnutls_session_t session, unsigned int htype,

+	unsigned post, unsigned int incoming)

+{

+	gnutls_priority_set_direct(session, "NORMAL:-KX-ALL:+ECDHE-RSA", NULL);

+	return 0;

+}

+	

+

+/* A very basic TLS client, with anonymous authentication.

+ */

+

+#define MAX_BUF 1024

+

+static void client(int fd)

+{

+	int ret;

+	char buffer[MAX_BUF + 1];

+	gnutls_certificate_credentials_t x509_cred;

+	gnutls_session_t session;

+	/* Need to enable anonymous KX specifically. */

+

+	global_init();

+

+	if (debug) {

+		gnutls_global_set_log_function(client_log_func);

+		gnutls_global_set_log_level(7);

+	}

+

+	gnutls_certificate_allocate_credentials(&x509_cred);

+

+	/* Initialize TLS session

+	 */

+	gnutls_init(&session, GNUTLS_CLIENT);

+

+	/* Use default priorities */

+	gnutls_priority_set_direct(session, "NORMAL:-KX-ALL:+ECDHE-RSA:-SIGN-ALL:+SIGN-RSA-MD5", NULL);

+

+	/* put the anonymous credentials to the current session

+	 */

+	gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, x509_cred);

+

+	gnutls_transport_set_int(session, fd);

+	gnutls_handshake_set_hook_function(session, GNUTLS_HANDSHAKE_SERVER_KEY_EXCHANGE,

+					   GNUTLS_HOOK_PRE,

+					   handshake_callback);

+

+	/* Perform the TLS handshake

+	 */

+	do {

+		ret = gnutls_handshake(session);

+	}

+	while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

+

+	if (ret == GNUTLS_E_UNSUPPORTED_SIGNATURE_ALGORITHM) {

+		/* success */

+		goto end;

+	}

+

+	if (ret < 0) {

+		terminate();

+		fail("client: Handshake failed: %s\n", gnutls_strerror(ret));

+		exit(1);

+	} else {

+		if (debug)

+			success("client: Handshake was completed\n");

+	}

+

+	if (gnutls_sign_algorithm_get(session) == GNUTLS_SIGN_RSA_MD5) {

+		terminate();

+		fail("client: MD5 was negotiated\n");

+		exit(1);

+	}

+	success("client: %s was negotiated\n", gnutls_sign_get_name(gnutls_sign_algorithm_get(session)));

+

+	if (debug)

+		success("client: TLS version is: %s\n",

+			gnutls_protocol_get_name

+			(gnutls_protocol_get_version(session)));

+

+	do {

+		do {

+			ret = gnutls_record_recv(session, buffer, MAX_BUF);

+		} while (ret == GNUTLS_E_AGAIN

+			 || ret == GNUTLS_E_INTERRUPTED);

+	} while (ret > 0);

+

+	if (ret == 0) {

+		if (debug)

+			success

+			    ("client: Peer has closed the TLS connection\n");

+		goto end;

+	} else if (ret < 0) {

+		terminate();

+		fail("client: Error: %s\n", gnutls_strerror(ret));

+		exit(1);

+	}

+

+	gnutls_bye(session, GNUTLS_SHUT_WR);

+

+      end:

+

+	close(fd);

+

+	gnutls_deinit(session);

+

+	gnutls_certificate_free_credentials(x509_cred);

+

+	gnutls_global_deinit();

+}

+

+

+/* These are global */

+pid_t child;

+

+static void terminate(void)

+{

+	kill(child, SIGTERM);

+	exit(1);

+}

+

+static void server(int fd)

+{

+	int ret;

+	char buffer[MAX_BUF + 1];

+	gnutls_session_t session;

+	gnutls_certificate_credentials_t x509_cred;

+

+	/* this must be called once in the program

+	 */

+	global_init();

+	memset(buffer, 0, sizeof(buffer));

+

+	if (debug) {

+		gnutls_global_set_log_function(server_log_func);

+		gnutls_global_set_log_level(4711);

+	}

+

+	gnutls_certificate_allocate_credentials(&x509_cred);

+	gnutls_certificate_set_x509_key_mem(x509_cred, &server_cert,

+					    &server_key,

+					    GNUTLS_X509_FMT_PEM);

+

+	gnutls_init(&session, GNUTLS_SERVER);

+

+	/* avoid calling all the priority functions, since the defaults

+	 * are adequate.

+	 */

+	gnutls_priority_set_direct(session, "NORMAL:-KX-ALL:+ECDHE-RSA:-SIGN-ALL:+SIGN-RSA-MD5", NULL);

+

+	gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, x509_cred);

+

+	gnutls_transport_set_int(session, fd);

+

+	do {

+		ret = gnutls_handshake(session);

+	} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

+	if (ret < 0) {

+		/* failure is expected here */

+		goto end;

+	}

+

+	if (debug) {

+		success("server: Handshake was completed\n");

+		success("server: %s was negotiated\n", gnutls_sign_get_name(gnutls_sign_algorithm_get(session)));

+	}

+

+	if (debug)

+		success("server: TLS version is: %s\n",

+			gnutls_protocol_get_name

+			(gnutls_protocol_get_version(session)));

+

+	/* do not wait for the peer to close the connection.

+	 */

+	gnutls_bye(session, GNUTLS_SHUT_WR);

+

+ end:

+	close(fd);

+	gnutls_deinit(session);

+

+	gnutls_certificate_free_credentials(x509_cred);

+

+	gnutls_global_deinit();

+

+	if (debug)

+		success("server: finished\n");

+}

+

+static void ch_handler(int sig)

+{

+	int status;

+	wait(&status);

+	if (WEXITSTATUS(status) != 0 ||

+	    (WIFSIGNALED(status) && WTERMSIG(status) == SIGSEGV)) {

+		if (WIFSIGNALED(status))

+			fail("Child died with sigsegv\n");

+		else

+			fail("Child died with status %d\n",

+			     WEXITSTATUS(status));

+		terminate();

+	}

+	return;

+}

+

+void doit(void)

+{

+	int fd[2];

+	int ret;

+

+	signal(SIGCHLD, ch_handler);

+

+	ret = socketpair(AF_UNIX, SOCK_STREAM, 0, fd);

+	if (ret < 0) {

+		perror("socketpair");

+		exit(1);

+	}

+

+	child = fork();

+	if (child < 0) {

+		perror("fork");

+		fail("fork");

+		exit(1);

+	}

+

+	if (child) {

+		/* parent */

+		close(fd[1]);

+		client(fd[0]);

+		kill(child, SIGTERM);

+	} else {

+		close(fd[0]);

+		server(fd[1]);

+		exit(0);

+	}

+}

+

+#endif				/* _WIN32 */

-- 

2.5.0