I have close to 50 sites under my care. The hack happened almost 2 month ago. These three websites were hacked into had ONLY this plugin in common.
One compromised website was on a previous WordPress versions (one was on the 4.4 branch and two on the latest 4.5 branch). All three websites were updated to the latest security update automatically. One site had auto-update for everything (latest WP major version, security updates, themes and plugins). The websites had no themes or other plugins in common. The hacked sites had the same backdoor plugins installed after being hacked.
Upon close inspection:
– ucOptions.php allows direct access and manipulation of POST variables to write options without authorization, ATM, only POST & user access is filtered, I can still turn the under construction page on or off through [GET].
– Other .php files allow direct access too.
– Only some of the user supplied arguments are being sanitized.
I think there are more holes as the attacker was able to add new admin user accounts without me getting the notification.
I’ve cleaned these sites completely, new install, hashes, passwords and updated these sites with more security than the default plugin “limit login attempts”. Needless to say, this plugin isn’t going to be installed ever again.