Why are XML external entities useful in service oriented architectures?

Why are XML external entities useful in service oriented architectures?

It is the default standard for exchanging messages between enterprise applications in a Services Oriented Architecture. XML’s main advantages are its extensibility, acceptance (storage) of any type of data and it being an accepted public standard.

What does XML external entities XXE refer to?

XML external entity injection (also known as XXE) is a web security vulnerability that allows an attacker to interfere with an application’s processing of XML data.

What is blind XXE attack?

What is blind XXE? Blind XXE vulnerabilities arise where the application is vulnerable to XXE injection but does not return the values of any defined external entities within its responses.

What is out of band XXE?

In the case of out-of-band XXE attacks (also called blind XXE), there is no immediate response from the web application. To learn about in-band XXE vulnerabilities and attacks, read the following article: What Are XML External Entity (XXE) Attacks.

What does a DTD file do?

A DTD defines the valid building blocks of an XML document. It defines the document structure with a list of validated elements and attributes. A DTD can be declared inline inside an XML document, or as an external reference.

What is meant by DTD?

A document type definition (DTD) is a set of markup declarations that define a document type for an SGML-family markup language (GML, SGML, XML, HTML). A DTD defines the valid building blocks of an XML document. It defines the document structure with a list of validated elements and attributes.

Can a blind XXe attack work with an external DTD?

The preceding technique works fine with an external DTD, but it won’t normally work with an internal DTD that is fully specified within the DOCTYPE element. This is because the technique involves using an XML parameter entity within the definition of another parameter entity.

Which is an example of a blind XXe attack?

For example, suppose there is a DTD file on the server filesystem at the location /usr/local/app/schema.dtd, and this DTD file defines an entity called custom_entity. An attacker can trigger an XML parsing error message containing the contents of the /etc/passwd file by submitting a hybrid DTD like the following:

How does an XML parser interpret an external DTD?

This XXE payload declares an XML parameter entity called xxe and then uses the entity within the DTD. This will cause the XML parser to fetch the external DTD from the attacker’s server and interpret it inline. The steps defined within the malicious DTD are then executed, and the /etc/passwd file is transmitted to the attacker’s server.

Can a DTD be loaded from an external location?

This means that an attacker can employ the error-based XXE technique from within an internal DTD, provided the XML parameter entity that they use is redefining an entity that is declared within an external DTD. Of course, if out-of-band connections are blocked, then the external DTD cannot be loaded from a remote location.