== Why is this an issue?

include::../description.adoc[]
=== 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], https://docs.oracle.com/javase/9/docs/api/javax/xml/stream/XMLInputFactory.html[XMLInput], https://docs.oracle.com/javase/9/docs/api/javax/xml/transform/TransformerFactory.html[Transformer] and https://docs.oracle.com/javase/9/docs/api/javax/xml/validation/SchemaFactory.html[Schema] JAPX factories:

[source,java]
----
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); // Noncompliant

SAXParserFactory factory = SAXParserFactory.newInstance(); // Noncompliant

XMLInputFactory factory = XMLInputFactory.newInstance(); // Noncompliant

TransformerFactory factory = javax.xml.transform.TransformerFactory.newInstance();  // Noncompliant

SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);  // Noncompliant
----

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

[source,java]
----
SAXReader xmlReader = new SAXReader(); // Noncompliant
----

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

[source,java]
----
SAXBuilder builder = new SAXBuilder(); // 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], https://docs.oracle.com/javase/9/docs/api/javax/xml/stream/XMLInputFactory.html[XMLInput], https://docs.oracle.com/javase/9/docs/api/javax/xml/transform/TransformerFactory.html[Transformer] and https://docs.oracle.com/javase/9/docs/api/javax/xml/validation/SchemaFactory.html[Schema] JAPX factories:

[source,java]
----
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
// to be compliant, completely disable DOCTYPE declaration:
factory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true); 
// or completely disable external entities declarations:     
factory.setFeature("http://xml.org/sax/features/external-general-entities", false); 
factory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
// or prohibit the use of all protocols by external entities:
factory.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, "");
factory.setAttribute(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
// or disable entity expansion but keep in mind that this doesn't prevent fetching external entities
// and this solution is not correct for OpenJDK < 13 due to a bug: https://bugs.openjdk.java.net/browse/JDK-8206132
factory.setExpandEntityReferences(false);


SAXParserFactory factory = SAXParserFactory.newInstance();
// to be compliant, completely disable DOCTYPE declaration:
factory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true); 
// or completely disable external entities declarations:     
factory.setFeature("http://xml.org/sax/features/external-general-entities", false); 
factory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
// or prohibit the use of all protocols by external entities:
SAXParser parser = factory.newSAXParser(); // Noncompliant
parser.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");
parser.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");

XMLInputFactory factory = XMLInputFactory.newInstance();
// to be compliant, completely disable DOCTYPE declaration:
factory.setProperty(XMLInputFactory.SUPPORT_DTD, false); 
// or completely disable external entities declarations:     
factory.setProperty(XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES, Boolean.FALSE);
// or prohibit the use of all protocols by external entities:
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");

TransformerFactory factory = javax.xml.transform.TransformerFactory.newInstance();
// to be compliant, prohibit the use of all protocols by external entities:
factory.setAttribute(XMLConstants.ACCESS_EXTERNAL_DTD, "");
factory.setAttribute(XMLConstants.ACCESS_EXTERNAL_STYLESHEET, "");

SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
// to be compliant, completely disable DOCTYPE declaration:
factory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true); 
// or prohibit the use of all protocols by external entities:
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");
factory.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
----

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

[source,java]
----
SAXReader xmlReader = new SAXReader();
xmlReader.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
----

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

[source,java]
----
SAXBuilder builder = new SAXBuilder(); 
builder.setProperty(XMLConstants.ACCESS_EXTERNAL_DTD, "");
builder.setProperty(XMLConstants.ACCESS_EXTERNAL_SCHEMA, "");
----

== Resources

* https://owasp.org/Top10/A05_2021-Security_Misconfiguration/[OWASP Top 10 2021 Category A5] - Security Misconfiguration
* 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://owasp.org/www-project-top-ten/2017/A4_2017-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]
* https://cwe.mitre.org/data/definitions/611[MITRE, CWE-611] - Information Exposure Through XML External Entity Reference
* https://cwe.mitre.org/data/definitions/827[MITRE, CWE-827] - Improper Control of Document Type Definition

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== Implementation Specification
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== Comments And Links
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