Today we’re gonna talk about a fun little trick called “Remote Schema Poisoning in XML.” It’s like regular old schema poisoning but with an extra step that involves sending your data to some random server on the internet.

So what is Remote Schema Poisoning in XML? Well, let’s start with regular old schema poisoning first. This is when an attacker sends malicious data to your application that includes a reference to their own custom schema. Your application then uses this custom schema instead of the one you intended and processes the data incorrectly or even crashes entirely.

But what if we could take it up a notch? What if we could send our malicious data to some random server on the internet, have that server process it for us, and then return the results back to our application? That’s where Remote Schema Poisoning in XML comes in!

Here’s how it works:
1. The attacker sends their malicious data with a reference to a custom schema hosted on some random server (let’s call this the “poisoned” schema).
2. Your application uses the poisoned schema instead of your intended one and processes the data incorrectly or even crashes entirely.
3. The attacker’s custom schema includes a reference to another server (let’s call this the “poisoning” server) that will process their malicious data for them.
4. Your application sends the malicious data to the poisoning server and processes its results instead of your intended ones.
5. The attacker now has access to sensitive information or can execute arbitrary code on your system!

Sounds pretty cool, right? But let’s be real here, this is not a good thing. In fact, it’s a terrible thing that should never happen in any production environment. So how do we prevent Remote Schema Poisoning in XML from happening to us? Well, there are a few things you can do:
1. Disable external entities altogether (this will also help protect against XXE attacks).
2. Use a whitelist of trusted schemas and only allow those to be used by your application.
3. Implement input validation on all incoming data to ensure that it conforms to your intended schema.
4. Keep your software up-to-date with the latest security patches!