Add XMLFilterParseStringTest.

Author: garydgregory

src/test/java/org/apache/commons/xml/XMLFilterParseStringTest.java

@@ -0,0 +1,67 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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
+ *
+ *      https://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 org.apache.commons.xml;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+import java.io.StringReader;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import javax.xml.transform.Templates;
+import javax.xml.transform.sax.SAXTransformerFactory;
+import javax.xml.transform.stream.StreamSource;
+
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.xml.sax.XMLFilter;
+
+@Tag("trax")
+class XMLFilterParseStringTest {
+
+    private static final String IDENTITY_XSLT =
+    // @formatter:off
+        "<xsl:stylesheet version=\"1.0\" xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\">" +
+        "<xsl:template match=\"/\"><xsl:copy-of select=\".\"/></xsl:template>" +
+        "</xsl:stylesheet>";
+    // @formatter:on
+
+    private static String entityPayload() {
+        // @formatter:off
+        return "<?xml version=\"1.0\"?>\n" +
+               "<!DOCTYPE root [<!ENTITY xxe SYSTEM \"" + AttackTestSupport.resourceUrl("referenced.txt") + "\">]>\n" +
+               "<root>&xxe;</root>";
+        // @formatter:on
+    }
+
+    @Test
+    void hardenedFilterParseStringDoesNotLeakExternalEntity(@TempDir final Path tmpDir) throws Exception {
+        final SAXTransformerFactory factory = (SAXTransformerFactory) XmlFactories.newTransformerFactory();
+        final Templates templates = factory.newTemplates(new StreamSource(new StringReader(IDENTITY_XSLT)));
+        final XMLFilter filter = factory.newXMLFilter(templates);
+        final Path tmp = Files.createTempFile(tmpDir, "xmlfilter", ".xml");
+        Files.write(tmp, entityPayload().getBytes(StandardCharsets.UTF_8));
+        final StringBuilder out = new StringBuilder();
+        filter.setContentHandler(AttackTestSupport.capturingHandler(out));
+        // public API – XMLFilter.parse(String) – the path that ends in XMLFilterImpl.parse(String)
+        filter.parse(tmp.toUri().toString());
+        assertFalse(out.toString().contains(AttackTestSupport.LEAKED_MARKER), "external entity leaked through XMLFilter.parse(String)");
+    }
+}