The Fancy Product Designer plugin for WordPress is vulnerable to Server-Side Request Forgery in all versions up to, and including, 6.4.8. This is due to a time-of-check/time-of-use (TOCTOU) race condition in the url parameter of the fpd_custom_uplod_file AJAX action. The plugin validates the URL by calling getimagesize() first, then later retrieves the same URL using file_get_contents(). This makes it possible for unauthenticated attackers to exploit the timing gap to perform SSRF attacks by serving a valid image during validation, then changing the response to redirect to arbitrary internal or external URLs during the actual fetch.
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:
A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.