XXE stands for XML External Entity and before we understand the attack, lets understand what is XML first:
XML (eXtensible Markup Language) is a structured data format used by web applications to store and exchange information. It's like a standardized blueprint for data, making it easier for computers to understand and process. HTML describes how data should be displayed on a web page whereas XML defines the structure of the data itself.
Below mentioned is how XML data structure looks like:
<login>
<email>user@example.com</email>
<password>secretpassword</password>
</login>
Now, let’s dive deep into XXE injection:
Imagine a website that takes data from you in the form of XML (login xml structure mentioned above) and then processes it. If this website doesn't have proper security measures in place, a hacker could craft a malicious XML file to exploit a vulnerability known as XXE. These external entities can do harmful things like reading sensitive files on the server, initiating network requests to other systems, and potentially gaining unauthorized access to your data.
<!DOCTYPE login [
<!ELEMENT login ANY >
<!ENTITY xxe SYSTEM "file:///etc/passwd" >]>
<login>
<email>&xxe;</email>
<password>secretpassword</password>
</login>
In this XML document code above, an external entity &xxe; is introduced.This entity references the local file system using SYSTEM and tries to retrieve the contents of the /etc/passwd file. An attacker might use this technique to access sensitive system files. Properly secured applications should prevent such XXE attacks by disabling external entity processing.
By following these mitigation steps, you can help safeguard your web application against XXE vulnerabilities, protecting your data and system from potential attacks.
Input Validation: Ensure that the XML data coming into your web application is only from trusted sources. Don't allow untrusted or user-submitted XML to be processed.
Disable Entity Expansion: Disable the ability for XML entities to expand within the XML parser. This can help prevent the processing of malicious external entities.
Use a Modern XML Parser: Use a secure and up-to-date XML parser that has built-in security features to block XXE attacks.
Firewalls and Security Tools: Deploy web application firewalls (WAFs) and security scanning tools to detect and block XXE attacks.
Access Controls: Implement proper access controls to restrict who can access what on your web server. This limits the damage even if an XXE attack is successful.
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