The wp_ajax_update_plugin function in wp-admin/includes/ajax-actions.php in WordPress before 4.6 makes a get_plugin_data call before checking the update_plugins capability, which allows remote authenticated users to bypass intended read-access restrictions via the plugin parameter to wp-admin/admin-ajax.php, a related issue to CVE-2016-6896.
https://sumofpwn.nl/advisory/2016/path_traversal_vulnerability_in_wordpress_core_ajax_handlers.html
https://core.trac.wordpress.org/ticket/37490
https://core.trac.wordpress.org/changeset/38168