Save as PDF Plugin by PDFCrowd <= 4.6.1 - Authenticated (Contributor+) Arbitrary Function Invocation / Code Injection via 'pdf_created_callback' Shortcode Attribute

The Save as PDF Plugin by PDFCrowd plugin for WordPress is vulnerable to Arbitrary Function Invocation in all versions up to, and including, 4.6.1 via the `pdf_created_callback` shortcode attribute. The `eval_shortcode()` function copies any non-`button_`/non-`email_` shortcode attribute verbatim into a custom options array without sanitization, allowlist enforcement, or capability checks, and `create_button()` AES-encrypts that array — including the attacker-supplied callback value — and embeds the resulting blob in the rendered button HTML; when the blob is later POSTed to the unauthenticated `wp_ajax_nopriv_save_as_pdf_pdfcrowd` endpoint, `save_as_pdf_pdfcrowd()` decrypts it and invokes `$options['pdf_created_callback']` as a PHP callable at line 1722 with no `is_callable()` guard, no allowlist, and no capability check. This makes it possible for authenticated attackers, with Contributor-level access and above, to invoke arbitrary PHP functions or static class methods with plugin option data as the sole argument, enabling disclosure of the site's stored PDFCrowd API key and username or further server-side abuse. Note that the encryption boundary does not mitigate this vector because the server itself encrypts the attacker-chosen callback during shortcode rendering, supplying any authenticated Contributor with a cryptographically valid blob that any unauthenticated visitor can subsequently replay to trigger invocation.