SaxParserSafeEntityResolver.java

package testcode.xxe;

import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;

public class SaxParserSafeEntityResolver {

    public static class CustomResolver implements EntityResolver {
        public InputSource resolveEntity(String publicId, String systemId) throws SAXException, IOException {
            return new InputSource(); // Do not allow unknown entities, by returning blank path
        }
    }

    private static void receiveXMLStream(final InputStream inStream,
                                         final DefaultHandler defHandler)
            throws ParserConfigurationException, SAXException, IOException {
        // ...
        SAXParserFactory spf = SAXParserFactory.newInstance();
        final SAXParser saxParser = spf.newSAXParser();

        XMLReader reader = saxParser.getXMLReader();
        reader.setEntityResolver(new CustomResolver()); //Custom resolver
        InputSource is = new InputSource(inStream);
        reader.parse(is);
    }

    public static void main(String[] args) throws ParserConfigurationException,
            SAXException, IOException {

        String xmlString = "<?xml version=\"1.0\"?>" +
                "<!DOCTYPE foo SYSTEM \"C:/test\"><test>&foo;</test>"; // Tainted input

        InputStream is = new ByteArrayInputStream(xmlString.getBytes());
        receiveXMLStream(is, new DefaultHandler());
    }
}