Document XML parser usage against security false positives

Prior to this commit, our XML parser usage would be already haredened
against XXE (XML External Entities) attacks. Still, we recently received
several invalid security reports claiming that our setup should be
hardened.

This commit documents a few usages of XML parsers to add some more
context and hopefully prevent future invalid reports.

Closes gh-33713

Author: bclozel

spring-beans/src/main/java/org/springframework/beans/factory/xml/DefaultDocumentLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -88,6 +88,9 @@ public Document loadDocument(InputSource inputSource, EntityResolver entityResol
 	protected DocumentBuilderFactory createDocumentBuilderFactory(int validationMode, boolean namespaceAware)
 			throws ParserConfigurationException {
 
+		// This document loader is used for loading application configuration files.
+		// As a result, attackers would need complete write access to application configuration
+		// to leverage XXE attacks. This does not qualify as privilege escalation.
 		DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
 		factory.setNamespaceAware(namespaceAware);
 

spring-orm/src/main/java/org/springframework/orm/jpa/persistenceunit/PersistenceUnitReader.java

@@ -157,6 +157,9 @@ public SpringPersistenceUnitInfo[] readPersistenceUnitInfos(String[] persistence
 	Document buildDocument(ErrorHandler handler, InputStream stream)
 			throws ParserConfigurationException, SAXException, IOException {
 
+		// This document loader is used for loading application configuration files.
+		// As a result, attackers would need complete write access to application configuration
+		// to leverage XXE attacks. This does not qualify as privilege escalation.
 		DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
 		dbf.setNamespaceAware(true);
 		DocumentBuilder parser = dbf.newDocumentBuilder();

spring-oxm/src/main/java/org/springframework/oxm/jaxb/Jaxb2Marshaller.java

@@ -603,6 +603,9 @@ private Schema loadSchema(Resource[] resources, String schemaLanguage) throws IO
 		Assert.hasLength(schemaLanguage, "No schema language provided");
 		Source[] schemaSources = new Source[resources.length];
 
+		// This parser is used to read the schema resources provided by the application.
+		// The parser used for reading the source is protected against XXE attacks.
+		// See "processSource(Source source)".
 		SAXParserFactory saxParserFactory = this.schemaParserFactory;
 		if (saxParserFactory == null) {
 			saxParserFactory = SAXParserFactory.newInstance();
@@ -907,6 +910,8 @@ else if (streamSource.getReader() != null) {
 		}
 
 		try {
+			// By default, Spring will prevent the processing of external entities.
+			// This is a mitigation against XXE attacks.
 			if (xmlReader == null) {
 				SAXParserFactory saxParserFactory = this.sourceParserFactory;
 				if (saxParserFactory == null) {

spring-web/src/main/java/org/springframework/http/converter/xml/Jaxb2RootElementHttpMessageConverter.java

@@ -164,6 +164,8 @@ protected Source processSource(Source source) {
 		if (source instanceof StreamSource streamSource) {
 			InputSource inputSource = new InputSource(streamSource.getInputStream());
 			try {
+				// By default, Spring will prevent the processing of external entities.
+				// This is a mitigation against XXE attacks.
 				SAXParserFactory saxParserFactory = this.sourceParserFactory;
 				if (saxParserFactory == null) {
 					saxParserFactory = SAXParserFactory.newInstance();

spring-web/src/main/java/org/springframework/http/converter/xml/SourceHttpMessageConverter.java

@@ -177,6 +177,8 @@ else if (StreamSource.class == clazz || Source.class == clazz) {
 
 	private DOMSource readDOMSource(InputStream body, HttpInputMessage inputMessage) throws IOException {
 		try {
+			// By default, Spring will prevent the processing of external entities.
+			// This is a mitigation against XXE attacks.
 			DocumentBuilderFactory builderFactory = this.documentBuilderFactory;
 			if (builderFactory == null) {
 				builderFactory = DocumentBuilderFactory.newInstance();

spring-webmvc/src/main/java/org/springframework/web/servlet/view/xslt/XsltView.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -215,6 +215,9 @@ protected TransformerFactory newTransformerFactory(
 			}
 		}
 		else {
+			// This transformer is used for local XSLT views only.
+			// As a result, attackers would need complete write access to application configuration
+			// to leverage XXE attacks. This does not qualify as privilege escalation.
 			return TransformerFactory.newInstance();
 		}
 	}