Commit 5627f9f2 authored by Matt Caswell's avatar Matt Caswell
Browse files

Don't detect a downgrade where the server has a protocol version hole 



Reviewed-by: default avatarViktor Dukhovni <viktor@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/7013)
parent 3e7cb13d

ssl/statem/statem_lib.c

+10 −3
Original line number Diff line number Diff line
@@ -1665,9 +1665,16 @@ static void check_for_downgrade(SSL *s, int vers, DOWNGRADE *dgrd) 
    if (vers == TLS1_2_VERSION

            && ssl_version_supported(s, TLS1_3_VERSION, NULL)) {

        *dgrd = DOWNGRADE_TO_1_2;

    } else if (!SSL_IS_DTLS(s) && vers < TLS1_2_VERSION

            && (ssl_version_supported(s, TLS1_2_VERSION, NULL)

                || ssl_version_supported(s, TLS1_3_VERSION, NULL))) {

    } else if (!SSL_IS_DTLS(s)

            && vers < TLS1_2_VERSION

               /*

                * We need to ensure that a server that disables TLSv1.2

                * (creating a hole between TLSv1.3 and TLSv1.1) can still

                * complete handshakes with clients that support TLSv1.2 and

                * below. Therefore we do not enable the sentinel if TLSv1.3 is

                * enabled and TLSv1.2 is not.

                */

            && ssl_version_supported(s, TLS1_2_VERSION, NULL)) {

        *dgrd = DOWNGRADE_TO_1_1;

    } else {

        *dgrd = DOWNGRADE_NONE;

test/recipes/70-test_tls13downgrade.t

+11 −4
Original line number Diff line number Diff line
@@ -45,7 +45,7 @@ use constant { 
$proxy->filter(\&downgrade_filter);

my $testtype = DOWNGRADE_TO_TLS_1_2;

$proxy->start() or plan skip_all => "Unable to start up Proxy for tests";

plan tests => 5;

plan tests => 6;

ok(TLSProxy::Message->fail(), "Downgrade TLSv1.3 to TLSv1.2");



#Test 2: Downgrade from TLSv1.3 to TLSv1.1
@@ -74,13 +74,20 @@ ok(TLSProxy::Message->fail() 
   "Fallback from TLSv1.3");



SKIP: {

    skip "TLSv1.1 disabled", 1 if disabled("tls1_1");

    #Test 5: A protocol "hole" should not be detected as a downgrade

    skip "TLSv1.1 disabled", 2 if disabled("tls1_1");

    #Test 5: A client side protocol "hole" should not be detected as a downgrade

    $proxy->clear();

    $proxy->filter(undef);

    $proxy->clientflags("-no_tls1_2");

    $proxy->start();

    ok(TLSProxy::Message->success(), "TLSv1.2 protocol hole");

    ok(TLSProxy::Message->success(), "TLSv1.2 client-side protocol hole");



    #Test 6: A server side protocol "hole" should not be detected as a downgrade

    $proxy->clear();

    $proxy->filter(undef);

    $proxy->serverflags("-no_tls1_2");

    $proxy->start();

    ok(TLSProxy::Message->success(), "TLSv1.2 server-side protocol hole");

}



sub downgrade_filter