The Admin Columns plugin for WordPress is vulnerable to PHP Object Injection leading to Remote Code Execution in versions up to and including 7.0.18. This is due to the use of unserialize() without an allowed_classes restriction in the IdsToCollection::get_ids_from_string() function, which processes attacker-controlled post meta values without proper validation. This makes it possible for authenticated attackers with Contributor-level access and above to inject a serialized PHP object into a post's custom meta field and trigger arbitrary code execution by exploiting a bundled POP gadget chain, resulting in remote code execution as the web server user.