Privilege escalation in Pubjet plugin for WordPress via check-token

The Pubjet | پاب‌جت plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 5.4.8. This is due to the `checkToken()` AJAX handler — registered under `wp_ajax_pubjet-check-token` — performing no capability check and no nonce verification before unconditionally writing the attacker-supplied `token` GET parameter directly into the site-wide `pubjet_settings` option via `pubjet_update_setting()`, prior to any remote validation. This makes it possible for authenticated attackers, with Subscriber-level access and above, to overwrite the plugin's stored REST API credential with an attacker-chosen value, immediately elevating their effective privileges to those of an authorized Pubjet API client and enabling them to invoke otherwise-restricted endpoints — `createReportage`, `updateReportage`, `deleteReportage`, `toggleCopyright`, and `createBacklink` — to create, modify, and delete arbitrary reportage posts and manipulate plugin state that Subscribers cannot normally access. The privilege escalation is self-reinforcing: because `RestApi::isTokenValid()` authenticates solely by comparing the incoming `Authorization` header against the value returned by `pubjet_token()`, which reads from the same option the unprotected handler writes to, the attacker-planted token is trusted as legitimate on all subsequent requests.