InfiniteWP Client <= 1.13.9 - Authenticated (Admin+) SQL Injection via 'iwp_get_comments_*' Array Key

The InfiniteWP Client plugin for WordPress is vulnerable to SQL Injection via the get_comments action in versions up to, and including, 1.13.9. This is due to insufficient escaping on the array-key names supplied in the JSON request body before use in a SQL statement: IWP_MMB_Comment::get_comments() calls extract() on $args (which silently skips keys that are not valid PHP variable names) but a second foreach($args as $checkbox => $checkbox_val) processes every key, strips the 'iwp_get_comments_' prefix with str_replace(), wraps the remainder in single quotes, and imploded it into an IN(...) clause that is executed via $wpdb->get_results() with no prepare(). Because the request body is read from php://input and JSON-decoded, wp_magic_quotes() never touches the data, so quote characters in keys pass through unaltered. This makes it possible for authenticated attackers, with administrator-level access and above (an administrator can register their own public key via add_site using the plugin's WP-admin-generated activation_key and then issue signed get_comments requests), to append additional SQL queries into already existing queries that can be used to extract sensitive information from the database.