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From e10a362f69191506e73bfa31778da45f4c5df482 Mon Sep 17 00:00:00 2001
From: Daiki Ueno <dueno@redhat.com>
Date: Mon, 12 Oct 2020 17:42:01 +0000
Subject: [PATCH] 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
--HG--
extra : moz-landing-system : lando
---
gtests/ssl_gtest/ssl_tls13compat_unittest.cc | 33 ++++++++++++++++++++
lib/ssl/ssl3con.c | 18 ++++-
lib/ssl/sslimpl.h | 4 +
3 files changed, 52 insertions(+), 3 deletions(-)
diff --git a/nss/gtests/ssl_gtest/ssl_tls13compat_unittest.cc b/nss/gtests/ssl_gtest/ssl_tls13compat_unittest.cc
index 6905ed0c0..dcede798c 100644
--- a/nss/gtests/ssl_gtest/ssl_tls13compat_unittest.cc
+++ b/nss/gtests/ssl_gtest/ssl_tls13compat_unittest.cc
@@ -348,6 +348,39 @@ TEST_F(TlsConnectStreamTls13, ChangeCipherSpecBeforeClientHelloTwice) {
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);
+}
+
// If we negotiate 1.2, we abort.
TEST_F(TlsConnectStreamTls13, ChangeCipherSpecBeforeClientHello12) {
EnsureTlsSetup();
diff --git a/nss/lib/ssl/ssl3con.c b/nss/lib/ssl/ssl3con.c
index 8be53d357..5f22872f8 100644
--- a/nss/lib/ssl/ssl3con.c
+++ b/nss/lib/ssl/ssl3con.c
@@ -6645,7 +6645,11 @@ ssl_CheckServerSessionIdCorrectness(sslSocket *ss, SECItem *sidBytes)
/* 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. */
@@ -8692,6 +8696,7 @@ ssl3_HandleClientHello(sslSocket *ss, PRUint8 *b, PRUint32 length)
errCode = PORT_GetError();
goto alert_loser;
}
+ ss->ssl3.hs.allowCcs = PR_TRUE;
}
/* TLS 1.3 requires that compression include only null. */
@@ -13061,8 +13066,15 @@ ssl3_HandleRecord(sslSocket *ss, SSL3Ciphertext *cText)
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 --git a/nss/lib/ssl/sslimpl.h b/nss/lib/ssl/sslimpl.h
index b0e44a088..44c43a0e6 100644
--- a/nss/lib/ssl/sslimpl.h
+++ b/nss/lib/ssl/sslimpl.h
@@ -710,6 +710,10 @@ typedef struct SSL3HandshakeStateStr {
* 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 */
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