KREST-7955 421 misdirected request if host does not match SNI

core/src/main/java/io/confluent/rest/Application.java

@@ -29,6 +29,7 @@
 import io.confluent.rest.exceptions.JsonParseExceptionMapper;
 import io.confluent.rest.extension.ResourceExtension;
 import io.confluent.rest.filters.CsrfTokenProtectionFilter;
+import io.confluent.rest.handlers.SniHandler;
 import io.confluent.rest.metrics.Jetty429MetricsDosFilterListener;
 import io.confluent.rest.metrics.JettyRequestMetricsFilter;
 import io.confluent.rest.metrics.MetricsResourceMethodApplicationListener;
@@ -412,6 +413,10 @@ public Handler configureHandler() {
     requestLogHandler.setRequestLog(requestLog);
     context.insertHandler(requestLogHandler);
 
+    if (config.getSniCheckEnable()) {
+      context.insertHandler(new SniHandler());
+    }
+
     HandlerCollection handlers = new HandlerCollection();
     handlers.setHandlers(new Handler[]{context});
 

core/src/main/java/io/confluent/rest/RestConfig.java

@@ -495,6 +495,12 @@ public class RestConfig extends AbstractConfig {
           + "Java 11 JVM or later. Default is true.";
   protected static final boolean HTTP2_ENABLED_DEFAULT = true;
 
+  public static final String SNI_CHECK_ENABLED_CONFIG = "sni.check.enabled";
+  protected static final String SNI_CHECK_ENABLED_DOC =
+      "Whether or not to check the SNI against the Host header. If the values don't match, "
+          + "returns a 421 misdirected response. Default is false.";
+  protected static final boolean SNI_CHECK_ENABLED_DEFAULT = false;
+
   public static final String PROXY_PROTOCOL_ENABLED_CONFIG =
       "proxy.protocol.enabled";
   protected static final String PROXY_PROTOCOL_ENABLED_DOC =
@@ -1053,6 +1059,12 @@ private static ConfigDef incompleteBaseConfigDef() {
             HTTP2_ENABLED_DEFAULT,
             Importance.LOW,
             HTTP2_ENABLED_DOC
+        ).define(
+            SNI_CHECK_ENABLED_CONFIG,
+            Type.BOOLEAN,
+            SNI_CHECK_ENABLED_DEFAULT,
+            Importance.LOW,
+            SNI_CHECK_ENABLED_DOC
         ).define(
             LISTENER_PROTOCOL_MAP_CONFIG,
             Type.LIST,
@@ -1391,6 +1403,10 @@ public final int getNetworkTrafficRateLimitBytesPerSec() {
     return getInt(NETWORK_TRAFFIC_RATE_LIMIT_BYTES_PER_SEC_CONFIG);
   }
 
+  public final boolean getSniCheckEnable() {
+    return getBoolean(SNI_CHECK_ENABLED_CONFIG);
+  }
+
   /**
    * <p>A helper method for extracting multi-instance application configuration,
    * specified via property names of the form PREFIX[.LISTENER_NAME].PROPERTY.</p>

core/src/main/java/io/confluent/rest/handlers/SniHandler.java

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2014 - 2023 Confluent Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.confluent.rest.handlers;
+
+import static org.eclipse.jetty.http.HttpStatus.Code.MISDIRECTED_REQUEST;
+
+import java.io.IOException;
+import java.util.List;
+import javax.net.ssl.ExtendedSSLSession;
+import javax.net.ssl.SNIHostName;
+import javax.net.ssl.SNIServerName;
+import javax.net.ssl.SSLSession;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import org.eclipse.jetty.io.EndPoint;
+import org.eclipse.jetty.io.ssl.SslConnection.DecryptedEndPoint;
+import org.eclipse.jetty.server.Request;
+import org.eclipse.jetty.server.handler.HandlerWrapper;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class SniHandler extends HandlerWrapper {
+  private static final Logger log = LoggerFactory.getLogger(SniHandler.class);
+
+  @Override
+  public void handle(String target, Request baseRequest,
+      HttpServletRequest request,
+      HttpServletResponse response) throws IOException, ServletException {
+    String serverName = request.getServerName();
+    String sniServerName = getSniServerName(baseRequest);
+    if (sniServerName != null && !sniServerName.equals(serverName)) {
+      log.debug("Sni check failed, host header: {}, sni value: {}", serverName, sniServerName);
+      baseRequest.setHandled(true);
+      response.sendError(MISDIRECTED_REQUEST.getCode(), MISDIRECTED_REQUEST.getMessage());
+    }
+    super.handle(target, baseRequest, request, response);
+  }
+
+  private static String getSniServerName(Request baseRequest) {
+    EndPoint endpoint = baseRequest.getHttpChannel().getEndPoint();
+    if (endpoint instanceof DecryptedEndPoint) {
+      SSLSession session = ((DecryptedEndPoint) endpoint)
+          .getSslConnection()
+          .getSSLEngine()
+          .getSession();
+      if (session instanceof ExtendedSSLSession) {
+        List<SNIServerName> servers = ((ExtendedSSLSession) session).getRequestedServerNames();
+        if (servers != null) {
+          return servers.stream()
+              .findAny()
+              .filter(SNIHostName.class::isInstance)
+              .map(SNIHostName.class::cast)
+              .map(SNIHostName::getAsciiName)
+              .orElse(null);
+        }
+      }
+    }
+    return null;
+  }
+}