XML Entity Expansion (XEE) Attack
XML Entity Expansion (XEE) Attack is a type of security vulnerability that can allow an attacker to overload a system by exploiting the way XML parsers work. An XML parser reads XML data and creates an object model of the data in memory. When the parser encounters an entity reference in the XML, it replaces it with the content of the referenced entity. An entity reference is an XML construct that allows a document to reference data stored elsewhere, similar to a variable in a programming language.
An XEE attack occurs when an attacker injects XML data into an application that contains entity references that point to a large amount of data. If the XML parser is not configured to limit the size of the data that it processes, it will attempt to read and store all of the data referenced by the entity references. This can lead to a denial of service (DoS) attack, as the application will consume all available memory trying to process the data.
To protect against XEE attacks, it is important to configure XML parsers to limit the size of the data they process and to filter out potentially malicious entity references. Developers should also be careful when processing untrusted XML data, and never allow user input to be used in entity references.