The Easy PHP Settings plugin for WordPress is vulnerable to PHP Code Injection in all versions up to, and including, 1.0.4 via the `update_wp_memory_constants()` method. This is due to insufficient input validation on the `wp_memory_limit` and `wp_max_memory_limit` settings before writing them to `wp-config.php`. The `sanitize_text_field()` function used for sanitization does not filter single quotes, allowing an attacker to break out of the string context in a PHP `define()` statement. This makes it possible for authenticated attackers, with Administrator-level access and above, to inject and execute arbitrary PHP code on the server by modifying `wp-config.php`, which is loaded on every page request.