![]() This approach is effective for applications that return a resulting error message in their response. One way to exploit blind XXE vulnerabilities is to trigger parsing errors to generate an error message containing sensitive data. Blind XXE Exploit to Generate Error Messages Attackers cannot directly retrieve server-side files but can still detect and exploit blind XXE vulnerabilities with advanced methods like out-of-band data exfiltration or triggering an XML parsing error to disclose sensitive information. XXE vulnerabilities are often blind, meaning that the application doesn’t return any values of external entities. In some cases, the attacker can only perform a blind SSRG attack and cause damage without viewing the response. It allows the attacker to view responses from the URL in an application’s response, enabling interaction with the back end. This attack involves defining an external entity with the target URL and using the entity in the response’s data value. XXE Exploit to Perform SSRFĪttackers can use an XXE attack to perform server-side request forgery (SSRF), inducing the application to make requests to malicious URLs. The attacker then edits the XML data value in the response. The attacker introduces a DOCTYPE element defining an external entity that contains a path to the file. There are several types of XML external entity attacks: XXE Exploit to Retrieve FilesĪn XXE attack can retrieve an arbitrary file from the target server’s filesystem by modifying the submitted XML. If the XML parser is configured to process external entities, the web server will return the contents of that file. ![]() The XML parser will process this URI and add the resulting content into an XML document.įor example, an attacker can make the following request using a URI that points to a sensitive file on the server. ![]() It is possible to define external entities using URIs. XML files might contain document type definitions (DTDs) that allow defining and consuming XML entities. If too many processes or threads are not released, it can negatively impact application availability. Impacting application availability-some XML attacks might allow actors to access local resources that do not stop returning data.Remote code execution-if the XML processor library is vulnerable to client-side memory corruption, a threat actor can dereference a malicious URI to allow arbitrary code execution under the application account.Threat actors can use this trusted application to move to different internal systems. Expanding the attack-XXE attacks rely on the application that processes the XML document.Disclosing local files-threat actors can disclose files containing sensitive data, like passwords, using file: schemes or relative paths in the system identifier.Here are common consequences of XXE attacks: It is difficult to ascertain which parts of the application process XML, and in some cases, application owners have no access to the configuration of the XML parser used by specific components. However, in practice, web applications can contain a large number of components, each of which might include an XML parser. In theory, it is easy to prevent by setting XML parser configuration to disallow custom document type definitions (DTD). XXE vulnerabilities are caused by XML parsers that are outdated or not properly configured. Threat actors that successfully exploit XXE vulnerabilities can interact with systems the application can access, view files on the server, and in some cases, perform remote code execution (RCE). XML external entity injection (XXE) is a security vulnerability that allows a threat actor to inject unsafe XML entities into a web application that processes XML data.
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