XXE - XEE - XML External Entity

👉 Overview

👀 What ?

XML External Entity (XXE) is a type of attack against an application that parses XML input. This attack occurs when XML input containing a reference to an external entity is processed by a weakly configured XML parser. This attack can lead to the disclosure of confidential data, denial of service, server side request forgery, port scanning from the perspective of the machine where the parser is located, and other system impacts.

🧐 Why ?

Understanding XXE attacks is crucial to ensure the security of applications that parse XML input. An XXE attack can lead to serious security vulnerabilities, including disclosure of confidential data, denial of service, and possible command execution. Therefore, developers and security professionals need to be aware of this type of attack to prevent potential security breaches.

⛏️ How ?

To prevent XXE attacks, developers can disable the use of external entities in XML. If this is not possible, they can use less complex data formats such as JSON, and avoid serialization of sensitive data. Regular updates and security patches can also help prevent XXE attacks. In addition, regular security testing and code reviews can help detect potential XXE vulnerabilities.

⏳ When ?

XXE vulnerabilities have been known since the 2000s when XML was becoming a standard data exchange format. Despite being a well-known vulnerability, XXE issues are still found in software, often resulting in severe security risks.

⚙️ Technical Explanations

XML external entity injection (XXE) is a web security vulnerability that allows an attacker to interfere with an application's processing of XML data. It occurs when an application uses untrusted XML input that references an external entity. The attacker can inject malicious data, causing the XML parser to access unauthorized data. The XXE attack can also enable an attacker to cause a denial of service attack (DoS) by slowing down the system or making it unresponsive. To prevent XXE, developers should disable DTDs (Document Type Definitions), which is the feature that XXE attacks exploit. If this is not possible, they should use XML libraries that are not vulnerable to XXE, or configure their XML parser to not resolve external entities.