Description: XML External Entity is a type of attack that exploits the processing of XML inputs to manipulate external entities. This type of vulnerability occurs when a system that processes XML documents allows the inclusion of external entities, which can lead to the exposure of sensitive information, unauthorized command execution, or denial of service. External entities are references within an XML document that can point to external resources, such as local files or URLs. If an attacker can control these references, they can access data that should not be accessible or even execute malicious code. Exploiting these vulnerabilities is known as an XXE (XML External Entity) attack. The importance of understanding and mitigating these vulnerabilities lies in their ability to compromise the security of web applications and systems that rely on XML processing, potentially resulting in data leaks or service disruptions. Therefore, it is crucial for developers to implement secure coding practices and properly validate XML inputs to prevent these attacks.
History: The XML External Entity vulnerability was first identified in the context of web applications processing XML in the early 2000s. As the use of XML expanded in various applications and web services, so did the security concerns associated with its processing. In 2007, OWASP (Open Web Application Security Project) included the XXE attack in its list of top security vulnerabilities, which helped raise awareness about this type of risk. Since then, various guidelines and best practices have been developed to mitigate these vulnerabilities in applications using XML.
Uses: XML external entities are primarily used in applications that process data in XML format, such as web services, APIs, and content management systems. However, their use can be risky if adequate security measures are not implemented. In some cases, external entities are intentionally used to access external resources, such as configuration files or data from other applications. However, this should be done with caution and under strict access control measures to prevent abuse.
Examples: A notable example of an XXE attack occurred in 2017 when an attacker exploited a vulnerability in an XML processing service of a document management application, allowing access to sensitive files on the server. Another case occurred in 2019, where an XXE vulnerability in content management software allowed an attacker to access internal data and execute commands on the server. These incidents highlight the importance of properly validating and sanitizing XML inputs in web applications.
