Missing XML Validation

Description

Most successful attacks begin with a violation of the programmer's assumptions. By accepting an XML document without validating it against a DTD or XML schema, the programmer leaves a door open for attackers to provide unexpected, unreasonable, or malicious input.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

The following code loads and parses an XML file.

// Read DOM
try {
  ...
  DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
  factory.setValidating( false );
  ....
  c_dom = factory.newDocumentBuilder().parse( xmlFile );
} catch(Exception ex) {
  ...
}

The XML file is loaded without validating it against a known XML Schema or DTD.

Example Two

The following code creates a DocumentBuilder object to be used in building an XML document.

DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
builderFactory.setNamespaceAware(true);
DocumentBuilder builder = builderFactory.newDocumentBuilder();

The DocumentBuilder object does not validate an XML document against a schema, making it possible to create an invalid XML document.

See Also