This XXE payload declares an XML parameter entity called xxe and then uses the entity within the DTD. This means that you can test for blind XXE using out-of-band detection via XML parameter entities as follows: First, the declaration of an XML parameter entity includes the percent character before the entity name:Īnd second, parameter entities are referenced using the percent character instead of the usual ampersand: For present purposes, you only need to know two things.
XML parameter entities are a special kind of XML entity which can only be referenced elsewhere within the DTD. In this situation, you might be able to use XML parameter entities instead. Sometimes, XXE attacks using regular entities are blocked, due to some input validation by the application or some hardening of the XML parser that is being used. LAB Blind XXE with out-of-band interaction The attacker can monitor for the resulting DNS lookup and HTTP request, and thereby detect that the XXE attack was successful. This XXE attack causes the server to make a back-end HTTP request to the specified URL. You would then make use of the defined entity in a data value within the XML. For example, you would define an external entity as follows: You can often detect blind XXE using the same technique as for XXE SSRF attacks but triggering the out-of-band network interaction to a system that you control. You can trigger XML parsing errors in such a way that the error messages contain sensitive data.ĭetecting blind XXE using out-of-band ( OAST) techniques You can trigger out-of-band network interactions, sometimes exfiltrating sensitive data within the interaction data. There are two broad ways in which you can find and exploit blind XXE vulnerabilities: This means that direct retrieval of server-side files is not possible, and so blind XXE is generally harder to exploit than regular XXE vulnerabilities. In this section, we'll explain what blind XXE injection is and describe various techniques for finding and exploiting blind XXE vulnerabilities.īlind 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. Twitter WhatsApp Facebook Reddit LinkedIn Email
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