Filter out invalid URI in the error message of no handler found for a…

… REST request

Signed-off-by: Tianli Feng <ftianli@amazon.com>

server/src/main/java/org/opensearch/rest/RestController.java

@@ -56,6 +56,7 @@
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.net.URI;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -488,9 +489,14 @@ private void handleBadRequest(String uri, RestRequest.Method method, RestChannel
         try (XContentBuilder builder = channel.newErrorBuilder()) {
             builder.startObject();
             {
-                // Escaping HTML special characters in the error message only aims to satisfy common security scanners.
-                // There is no vulnerability without escaping, because the response MIME type is application/json, no scripts will be run.
-                builder.field("error", "no handler found for uri [" + escapeHtml(uri) + "] and method [" + method + "]");
+                try {
+                    // Validate input URI to filter out HTML special characters in the error message,
+                    // in case false-positive cross site scripting vulnerability is detected by common security scanners.
+                    uri = new URI(uri).getPath();
+                    builder.field("error", "no handler found for uri [" + uri + "] and method [" + method + "]");
+                } catch (Exception e) {
+                    builder.field("error", "invalid uri has been requested");
+                }
             }
             builder.endObject();
             channel.sendResponse(new BytesRestResponse(BAD_REQUEST, builder));
@@ -580,24 +586,4 @@ private static CircuitBreaker inFlightRequestsBreaker(CircuitBreakerService circ
         // We always obtain a fresh breaker to reflect changes to the breaker configuration.
         return circuitBreakerService.getBreaker(CircuitBreaker.IN_FLIGHT_REQUESTS);
     }
-
-    /**
-     * Perform an HTML escape operation on a String input to prevent XSS vulnerability.
-     * @param text the String to be escaped.
-     * @return The escaped result String.
-     */
-    private String escapeHtml(String text) {
-        StringBuilder out = new StringBuilder();
-        for (int i = 0; i < text.length(); i++) {
-            char c = text.charAt(i);
-            if (c == '"' || c == '\'' || c == '<' || c == '>' || c == '&') {
-                out.append("&#");
-                out.append((int) c);
-                out.append(';');
-            } else {
-                out.append(c);
-            }
-        }
-        return out.toString();
-    }
 }

server/src/test/java/org/opensearch/rest/RestControllerTests.java

@@ -559,10 +559,7 @@ public void testHandleBadRequestWithHtmlSpecialCharsInUri() {
         ).build();
         final AssertingChannel channel = new AssertingChannel(fakeRestRequest, true, RestStatus.BAD_REQUEST);
         restController.dispatchRequest(fakeRestRequest, channel, client.threadPool().getThreadContext());
-        assertThat(
-            channel.getRestResponse().content().utf8ToString(),
-            containsString("/<script>alert('xss');alert("&#x6A&#x61&#x76&#x61");</script>")
-        );
+        assertThat(channel.getRestResponse().content().utf8ToString(), containsString("invalid uri has been requested"));
     }
 
     public void testDispatchUnsupportedHttpMethod() {