The Drag and Drop Multiple File Upload for Contact Form 7 plugin for WordPress is vulnerable to PHP Object Injection in all versions up to, and including, 1.3.8.7 via deserialization of untrusted input from the dnd_upload_cf7_upload function. This makes it possible for attackers to inject a PHP Object through a PHAR file. No known POP chain is present in the vulnerable software, which means this vulnerability has no impact unless another plugin or theme containing a POP chain is installed on the site. If a POP chain is present via an additional plugin or theme installed on the target system, it may allow the attacker to perform actions like delete arbitrary files, retrieve sensitive data, or execute code depending on the POP chain present. This vulnerability may be exploited by unauthenticated attackers when a form is present on the site with the file upload action. The Flamingo plugin must be installed and activated in order to exploit the vulnerability.
The product deserializes untrusted data without sufficiently verifying that the resulting data will be valid.
It is often convenient to serialize objects for communication or to save them for later use. However, deserialized data or code can often be modified without using the provided accessor functions if it does not use cryptography to protect itself. Furthermore, any cryptography would still be client-side security – which is a dangerous security assumption. Data that is untrusted can not be trusted to be well-formed. When developers place no restrictions on “gadget chains,” or series of instances and method invocations that can self-execute during the deserialization process (i.e., before the object is returned to the caller), it is sometimes possible for attackers to leverage them to perform unauthorized actions, like generating a shell.