XXE Injection

Table of Contents

Here is a vulnerable Java code snippet that is susceptible to XXE (XML External Entity) injection attacks:

🥺 Vulnerable Code #

import javax.xml.parsers.DocumentBuilderFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class XXEInjectionVulnerable {
public static void main(String[] args) throws Exception {
// Create a DocumentBuilderFactory
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

// Disable external entity resolution
factory.setFeature("http://xml.org/sax/features/external-general-entities", false);
factory.setFeature("http://xml.org/sax/features/external-parameter-entities", false);

// Parse the input file 
Document doc = factory.newDocumentBuilder().parse(args[0]);

// Get the username element
NodeList usernameElements = doc.getElementsByTagName("username");
Element usernameElement = (Element) usernameElements.item(0);

// Get the text content of the username element
String username = usernameElement.getTextContent();

// Save the username to the database 
saveUsernameToDatabase(username); 
}
private static void saveUsernameToDatabase(String username) {
// Save the username to the database
}
}

This code is vulnerable to XXE injection because it does not properly disable external entity resolution. An attacker could supply a malicious XML document that references an external entity, causing the XML parser to retrieve and parse the external entity. This could potentially lead to the disclosure of sensitive information or the execution of arbitrary code.

😎 Secure Code #

Here is an example of a secure version of the code that properly disables external entity resolution:

import javax.xml.parsers.DocumentBuilderFactory; 
import org.w3c.dom.Document; 
import org.w3c.dom.Element; 
import org.w3c.dom.Node; 
import org.w3c.dom.NodeList; 

public class XXEInjectionSecure { 
public static void main(String[] args) throws Exception { 
// Create a DocumentBuilderFactory 
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); 

// Disable external entity resolution 
factory.setFeature("http://xml.org/sax/features/external-general-entities", false); 
factory.setFeature("http://xml.org/sax/features/external-parameter-entities", false); 

// Parse the input file 
Document doc = factory.newDocumentBuilder().parse(args[0]); 

// Get the username element 
NodeList usernameElements = doc.getElementsByTagName("username"); 
Element usernameElement = (Element) usernameElements.item(0); 

// Get the text content of the username element 
String username = usernameElement.getTextContent(); 

// Save the username to the database saveUsernameToDatabase(username); 
} 

private static void saveUsernameToDatabase(String username) { 
// Save the username to the database 
} 
}

This code is secure because it properly disables external entity resolution by setting the “http://xml.org/sax/features/external-general-entities” and “http://xml.org/sax/features/external-parameter-entities” features to false on the DocumentBuilderFactory. This prevents the XML parser from resolving and parsing external entities, which in turn prevents XXE injection attacks.

It’s important to note that simply disabling external entity resolution is not enough to completely prevent XXE injection attacks. You should also validate the input XML document to ensure that it does not contain any malicious content, such as unbalanced tags or unexpected element types. Additionally, you should consider using a different XML parsing library that is less susceptible to XXE injection attacks, such as StAX (Streaming API for XML) or SAX (Simple API for XML).

Leave a Reply