Motors <= 1.4.111 - Missing Authorization to Authenticated (Subscriber+) Arbitrary Post Meta Modification via 'stm_mark_as_sold_car' Parameter

The Motors – Car Dealership & Classified Listings Plugin plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 1.4.111. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for authenticated attackers, with subscriber-level access and above, to mark or unmark any other user's car listing as sold by replaying a valid nonce harvested from their own listing against an arbitrary victim post ID, triggering a site-wide 'Sold' badge on the victim's listing and silently stripping its special_car featured post meta as a side effect. Exploitation requires the attacker to hold an active listing of their own (obtainable by a Subscriber via the plugin's add-listing form) in order to harvest a valid nonce for the 'stm_mark_as_sold_car' action, which can then be replayed against any other listing's post ID.