FreeScout is a lightweight free open source help desk and shared inbox built with PHP (Laravel framework). In versions 1.8.185 and below, there is a critical deserialization vulnerability in the /conversation/ajax endpoint that allows authenticated users with knowledge of the APP_KEY to achieve remote code execution. The vulnerability occurs when the application processes the attachments_all and attachments POST parameters through the insecure Helper::decrypt() function, which performs unsafe deserialization of user-controlled data without proper validation. This flaw enables attackers to create arbitrary objects and manipulate their properties, leading to complete compromise of the web application. This is fixed in version 1.8.186.
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.