Classified Listing <= 5.4.2 - Missing Authorization to Authenticated (Subscriber+) Feature Modification via Multiple AJAX Handlers ('listingId'/'id' Parameters)

The Classified Listing – Classified ads & Business Directory plugin for WordPress is vulnerable to Missing Authorization in all versions up to, and including, 5.4.2. This is due to a missing capability/ownership check on the gallery_image_update_as_feature AJAX handler (action: rtcl_fb_gallery_image_update_as_feature), which accepts a user-supplied listing ID and attachment ID and sets the featured image of a listing while only validating a nonce that is exposed to any logged-in user on the frontend listing-submission form. This makes it possible for authenticated attackers, with Subscriber-level access and above, to change the featured image of arbitrary listings they do not own.