# HG changeset patch
# User Daiki Ueno <dueno@redhat.com>
# Date 1602524521 0
# Node ID 57bbefa793232586d27cee83e74411171e128361
# Parent 6e3bc17f05086854ffd2b06f7fae9371f7a0c174
Bug 1641480, TLS 1.3: tighten CCS handling in compatibility mode, r=mt
This makes the server reject CCS when the client doesn't indicate the
use of the middlebox compatibility mode with a non-empty
ClientHello.legacy_session_id, or it sends multiple CCS in a row.
Differential Revision: https://phabricator.services.mozilla.com/D79994
Upstream-Status: Backport
CVE: CVE-2020-25648
Reference to upstream patch: https://hg.mozilla.org/projects/nss/rev/57bbefa793232586d27cee83e74411171e128361
Signed-off-by: Mathieu Dubois-Briand <mbriand@witekio.com>
diff --color -Naur nss-3.51.1_old/nss/gtests/ssl_gtest/ssl_tls13compat_unittest.cc nss-3.51.1/nss/gtests/ssl_gtest/ssl_tls13compat_unittest.cc
--- nss-3.51.1_old/nss/gtests/ssl_gtest/ssl_tls13compat_unittest.cc 2022-12-08 16:05:47.447142660 +0100
+++ nss-3.51.1/nss/gtests/ssl_gtest/ssl_tls13compat_unittest.cc 2022-12-08 16:12:32.645932052 +0100
@@ -348,6 +348,85 @@
client_->CheckErrorCode(SSL_ERROR_HANDSHAKE_UNEXPECTED_ALERT);
}
+// The server rejects a ChangeCipherSpec if the client advertises an
+// empty session ID.
+TEST_F(TlsConnectStreamTls13, ChangeCipherSpecAfterClientHelloEmptySid) {
+ EnsureTlsSetup();
+ ConfigureVersion(SSL_LIBRARY_VERSION_TLS_1_3);
+
+ StartConnect();
+ client_->Handshake(); // Send ClientHello
+ client_->SendDirect(DataBuffer(kCannedCcs, sizeof(kCannedCcs))); // Send CCS
+
+ server_->ExpectSendAlert(kTlsAlertUnexpectedMessage);
+ server_->Handshake(); // Consume ClientHello and CCS
+ server_->CheckErrorCode(SSL_ERROR_RX_MALFORMED_CHANGE_CIPHER);
+}
+
+// The server rejects multiple ChangeCipherSpec even if the client
+// indicates compatibility mode with non-empty session ID.
+TEST_F(Tls13CompatTest, ChangeCipherSpecAfterClientHelloTwice) {
+ EnsureTlsSetup();
+ ConfigureVersion(SSL_LIBRARY_VERSION_TLS_1_3);
+ EnableCompatMode();
+
+ StartConnect();
+ client_->Handshake(); // Send ClientHello
+ // Send CCS twice in a row
+ client_->SendDirect(DataBuffer(kCannedCcs, sizeof(kCannedCcs)));
+ client_->SendDirect(DataBuffer(kCannedCcs, sizeof(kCannedCcs)));
+
+ server_->ExpectSendAlert(kTlsAlertUnexpectedMessage);
+ server_->Handshake(); // Consume ClientHello and CCS.
+ server_->CheckErrorCode(SSL_ERROR_RX_MALFORMED_CHANGE_CIPHER);
+}
+
+// The client rejects a ChangeCipherSpec if it advertises an empty
+// session ID.
+TEST_F(TlsConnectStreamTls13, ChangeCipherSpecAfterServerHelloEmptySid) {
+ EnsureTlsSetup();
+ ConfigureVersion(SSL_LIBRARY_VERSION_TLS_1_3);
+
+ // To replace Finished with a CCS below
+ auto filter = MakeTlsFilter<TlsHandshakeDropper>(server_);
+ filter->SetHandshakeTypes({kTlsHandshakeFinished});
+ filter->EnableDecryption();
+
+ StartConnect();
+ client_->Handshake(); // Send ClientHello
+ server_->Handshake(); // Consume ClientHello, and
+ // send ServerHello..CertificateVerify
+ // Send CCS
+ server_->SendDirect(DataBuffer(kCannedCcs, sizeof(kCannedCcs)));
+ client_->ExpectSendAlert(kTlsAlertUnexpectedMessage);
+ client_->Handshake(); // Consume ClientHello and CCS
+ client_->CheckErrorCode(SSL_ERROR_RX_MALFORMED_CHANGE_CIPHER);
+}
+
+// The client rejects multiple ChangeCipherSpec in a row even if the
+// client indicates compatibility mode with non-empty session ID.
+TEST_F(Tls13CompatTest, ChangeCipherSpecAfterServerHelloTwice) {
+ EnsureTlsSetup();
+ ConfigureVersion(SSL_LIBRARY_VERSION_TLS_1_3);
+ EnableCompatMode();
+
+ // To replace Finished with a CCS below
+ auto filter = MakeTlsFilter<TlsHandshakeDropper>(server_);
+ filter->SetHandshakeTypes({kTlsHandshakeFinished});
+ filter->EnableDecryption();
+
+ StartConnect();
+ client_->Handshake(); // Send ClientHello
+ server_->Handshake(); // Consume ClientHello, and
+ // send ServerHello..CertificateVerify
+ // the ServerHello is followed by CCS
+ // Send another CCS
+ server_->SendDirect(DataBuffer(kCannedCcs, sizeof(kCannedCcs)));
+ client_->ExpectSendAlert(kTlsAlertUnexpectedMessage);
+ client_->Handshake(); // Consume ClientHello and CCS
+ client_->CheckErrorCode(SSL_ERROR_RX_MALFORMED_CHANGE_CIPHER);
+}
+
// If we negotiate 1.2, we abort.
TEST_F(TlsConnectStreamTls13, ChangeCipherSpecBeforeClientHello12) {
EnsureTlsSetup();
diff --color -Naur nss-3.51.1_old/nss/lib/ssl/ssl3con.c nss-3.51.1/nss/lib/ssl/ssl3con.c
--- nss-3.51.1_old/nss/lib/ssl/ssl3con.c 2022-12-08 16:05:47.471142833 +0100
+++ nss-3.51.1/nss/lib/ssl/ssl3con.c 2022-12-08 16:12:42.037994262 +0100
@@ -6711,7 +6711,11 @@
/* TLS 1.3: We sent a session ID. The server's should match. */
if (!IS_DTLS(ss) && (sentRealSid || sentFakeSid)) {
- return sidMatch;
+ if (sidMatch) {
+ ss->ssl3.hs.allowCcs = PR_TRUE;
+ return PR_TRUE;
+ }
+ return PR_FALSE;
}
/* TLS 1.3 (no SID)/DTLS 1.3: The server shouldn't send a session ID. */
@@ -8730,6 +8734,7 @@
errCode = PORT_GetError();
goto alert_loser;
}
+ ss->ssl3.hs.allowCcs = PR_TRUE;
}
/* TLS 1.3 requires that compression include only null. */
@@ -13058,8 +13063,15 @@
ss->ssl3.hs.ws != idle_handshake &&
cText->buf->len == 1 &&
cText->buf->buf[0] == change_cipher_spec_choice) {
- /* Ignore the CCS. */
- return SECSuccess;
+ if (ss->ssl3.hs.allowCcs) {
+ /* Ignore the first CCS. */
+ ss->ssl3.hs.allowCcs = PR_FALSE;
+ return SECSuccess;
+ }
+
+ /* Compatibility mode is not negotiated. */
+ alert = unexpected_message;
+ PORT_SetError(SSL_ERROR_RX_MALFORMED_CHANGE_CIPHER);
}
if (IS_DTLS(ss) ||
diff --color -Naur nss-3.51.1_old/nss/lib/ssl/sslimpl.h nss-3.51.1/nss/lib/ssl/sslimpl.h
--- nss-3.51.1_old/nss/lib/ssl/sslimpl.h 2022-12-08 16:05:47.471142833 +0100
+++ nss-3.51.1/nss/lib/ssl/sslimpl.h 2022-12-08 16:12:45.106014567 +0100
@@ -711,6 +711,10 @@
* or received. */
PRBool receivedCcs; /* A server received ChangeCipherSpec
* before the handshake started. */
+ PRBool allowCcs; /* A server allows ChangeCipherSpec
+ * as the middlebox compatibility mode
+ * is explicitly indicarted by
+ * legacy_session_id in TLS 1.3 ClientHello. */
PRBool clientCertRequested; /* True if CertificateRequest received. */
ssl3KEADef kea_def_mutable; /* Used to hold the writable kea_def
* we use for TLS 1.3 */