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== Noncompliant Code Example

For https://docs.oracle.com/javase/9/docs/api/javax/xml/parsers/DocumentBuilderFactory.html[DocumentBuilder], https://docs.oracle.com/javase/9/docs/api/javax/xml/parsers/SAXParserFactory.html[SAXParser] and https://docs.oracle.com/javase/9/docs/api/javax/xml/validation/SchemaFactory.html[Schema] JAPX factories:

----
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(true); // Noncompliant
factory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", true); // Noncompliant

SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setValidating(true); // Noncompliant
factory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", true); // Noncompliant

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
schemaFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", true); // Noncompliant
----

For https://dom4j.github.io/[Dom4j] library:

----
SAXReader xmlReader = new SAXReader(); // Noncompliant
xmlReader.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", true);  // Noncompliant

----

For http://www.jdom.org/[Jdom2] library:

----
SAXBuilder builder = new SAXBuilder(); 
builder.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", true); // Noncompliant
----

== Compliant Solution
For https://docs.oracle.com/javase/9/docs/api/javax/xml/parsers/DocumentBuilderFactory.html[DocumentBuilder], https://docs.oracle.com/javase/9/docs/api/javax/xml/parsers/SAXParserFactory.html[SAXParser] and https://docs.oracle.com/javase/9/docs/api/javax/xml/validation/SchemaFactory.html[Schema] JAPX factories:

----
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false); 

SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false); 

SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
schemaFactory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
----

For https://dom4j.github.io/[Dom4j] library:

----
SAXReader xmlReader = new SAXReader(); // Noncompliant
xmlReader.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false); 

----

For http://www.jdom.org/[Jdom2] library:

----
SAXBuilder builder = new SAXBuilder(); 
builder.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
----

== Exceptions
This rules does not raise an issue when an `EntityResolver` is set.
----
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(true);
DocumentBuilder builder = factory.newDocumentBuilder();
builder.setEntityResolver(new MyEntityResolver());

SAXBuilder builder = new SAXBuilder();
builder.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", true);
builder.setEntityResolver(new EntityResolver());
----

== See

* https://docs.oracle.com/en/java/javase/13/security/java-api-xml-processing-jaxp-security-guide.html#GUID-8CD65EF5-D113-4D5C-A564-B875C8625FAC[Oracle Java Documentation] - XML External Entity Injection Attack
* https://www.owasp.org/index.php/Top_10-2017_A4-XML_External_Entities_(XXE)[OWASP Top 10 2017 Category A4] - XML External Entities (XXE)
* https://cheatsheetseries.owasp.org/cheatsheets/XML_External_Entity_Prevention_Cheat_Sheet.html#java[OWASP XXE Prevention Cheat Sheet]
* http://cwe.mitre.org/data/definitions/611.html[MITRE, CWE-611] - Information Exposure Through XML External Entity Reference
* http://cwe.mitre.org/data/definitions/827.html[MITRE, CWE-827] - Improper Control of Document Type Definition

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== Comments And Links
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